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1

Nanoparticles of Ni in ZnO single crystal matrix  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles were produced in ZnO single crystals using ion implantation of Ni along the [0001] channelling direction of ZnO. The particles were identified by X-ray diffraction and magnetization measurements as a distribution of superparamagnetic nickel nanoparticles having diameters in the range 2 - 3 nm. The depth distribution and size of the particles were determined using Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). The obtained results agree with magnetization and X-ray diffraction (XRD) data. From the determined depth distribution, the density change of implanted region of the material modified by the implantation procedure was estimated.

Borges, R. P.; Ribeiro, B.; Cruz, M. M.; Godinho, M.; Wahl, U.; da Silva, R. C.; Gonçalves, A. P.; Magén, C.

2013-06-01

2

Controlled synthesis of oriented single-crystal ZnO nanotube arrays on transparent conductive substrates  

Microsoft Academic Search

Large-scale arrays of highly oriented single-crystal ZnO nanotubes (ZNTs) are successfully fabricated on transparent conductive substrates by a simple method from an aqueous solution at a low temperature (typically 85 °C). The tubular morphology of the ZnO nanostructures is formed by a defect-selective chemical etching of the electrodeposited ZnO nanorods. The size of the ZNT arrays is determined by that

Guang-Wei She; Xiao-Hong Zhang; Wen-Sheng Shi; Xia Fan; Jack C. Chang; Chun-Sing Lee; Shuit-Tong Lee; Chang-Hong Liu

2008-01-01

3

Bio-inspired synthesis of ZnO polyhedral single crystals under eggshell membrane direction  

NASA Astrophysics Data System (ADS)

A simple and versatile technique was developed to prepare hierarchical ZnO single crystals by introducing eggshell membrane (ESM) to a bio-inspired approach. Based on the control of nucleation and gestation, ZnO nanocrystallites could grow at three dimensions into polyhedral single crystals through a surface sol-gel process followed by a calcination treatment. Different from traditional wet chemical techniques, our synthetic process depends more on the restrictive or directing functions of the ESM biomacromolecules. The hierarchical ZnO nanostructures doped with polyhedral single crystallites could be desirable for catalysts, photoelectrochemical devices, especially solar cells.

Su, Huilan; Song, Fang; Dong, Qun; Li, Tuoqi; Zhang, Xin; Zhang, Di

2011-07-01

4

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

5

Photoelectrochemical Stability and Alteration Products of n-Type Single-Crystal ZnO Photoanodes  

SciTech Connect

The photoelectrochemical stability and surface-alteration characteristics of both doped and undoped n-type ZnO single-crystal photoanode electrodes have been investigated. The single-crystal ZnO photoanode properties were analyzed using current-voltage measurements plus spectral and time-dependent quantum-yield methods. These measurements revealed the presence of a distinct anodic peak and an accompanying cathodic surface degradation process at negative potentials. The features of this peak were found to depend on time as well as the NaOH concentration in the electrolyte, but they were independent of the presence of electrode illumination. Current measurements performed at the peak indicate that charging and discharging effects are apparently taking place at the semiconductor/electrolyte interface. This result is consistent with the significant reactive degradation that takes place on the ZnO single crystal photoanode surface and that ultimately leads to the reduction of the ZnO surface to Zn metal. The resulting Zn-metal reaction products create unusual, dendrite-like, surface alteration structural features that were analyzed using x-ray diffraction, energy-dispersive analysis, and scanning electron microscopy. The ZnO doping methods employed here are also shown to be an effective way of increasing the n-type character of the crystals. Higher doping levels result in smaller depletion widths and lower quantum yields, since the minority carrier diffusion lengths are very short in these materials.

Paulauskas, Irene E. [University of Tennessee, Knoxville (UTK); Jellison Jr, Gerald Earle [ORNL; Boatner, Lynn A [ORNL; Brown, G. M. [Oak Ridge National Laboratory (ORNL)

2011-01-01

6

Photoluminescence and positron annihilation spectroscopic investigation on a H(+) irradiated ZnO single crystal.  

PubMed

Low temperature photoluminescence and room temperature positron annihilation spectroscopy have been employed to investigate the defects incorporated by 6 MeV H(+) ions in a hydrothermally grown ZnO single crystal. Prior to irradiation, the emission from donor bound excitons is at 3.378 eV (10 K). The irradiation creates an intense and narrow emission at 3.368 eV (10 K). The intensity of this peak is nearly four times that of the dominant near band edge peak of the pristine crystal. The characteristic features of the 3.368 eV emission indicate its origin as a 'hydrogen at oxygen vacancy' type defect. The positron annihilation lifetime measurement reveals a single component lifetime spectrum for both the unirradiated (164 ± 1 ps) and irradiated crystal (175 ± 1 ps). It reflects the fact that the positron lifetime and intensity of the new irradiation driven defect species are a little higher compared to those in the unirradiated crystal. However, the estimated defect concentration, even considering the high dynamic defect annihilation rate in ZnO, comes out to be ?4 × 10(17) cm(-3) (using SRIM software). This is a very high defect concentration compared to the defect sensitivity of positron annihilation spectroscopy. A probable reason is the partial filling of the incorporated vacancies (positron traps), which in ZnO are zinc vacancies. The positron lifetime of ?175 ps (in irradiated ZnO) is consistent with recent theoretical calculations for partially hydrogen-filled zinc vacancies in ZnO. Passivation of oxygen vacancies by hydrogen is also reflected in the photoluminescence results. A possible reason for such vacancy filling (at both Zn and O sites) due to irradiation has also been discussed. PMID:22790024

Sarkar, A; Chakrabarti, Mahuya; Sanyal, D; Bhowmick, D; Dechoudhury, S; Chakrabarti, A; Rakshit, Tamita; Ray, S K

2012-08-15

7

Magnetic and transport properties of transition-metal implanted ZnO single crystals  

NASA Astrophysics Data System (ADS)

ZnO single crystals were implanted with Mn, Co and Ni with fluences between 1 × 1016 cm-2 and 1 × 1017 cm-2 and energy of 200 keV. Results indicate that aggregation of transition metal ions in the as implanted state occurs only in the case of Ni. After an annealing stage to recover the ZnO structure aggregation occurs for the higher fluences of all implanted species. For lower concentrations paramagnetic behaviour with magnetic moments close to those of individual ions is observed. No polarised impurity band is formed as a result of the presence of transition metal ions and all samples show electrical conduction by carriers in extended states of ZnO. Significant values of magnetoresistance are measured at low temperatures, where electrical transport is described by hopping mechanisms between localized states. The sign of the magnetoresistance is dependent of the doping ion and is correlated with the observed aggregation.

Borges, R. P.; Ribeiro, B.; Costa, A. R. G.; Silva, C.; da Silva, R. C.; Evans, G.; Gonçalves, A. P.; Cruz, M. M.; Godinho, M.

2011-01-01

8

Deep-level defects study of arsenic-implanted ZnO single crystal  

Microsoft Academic Search

Unintentionally doped n-type zinc oxide (ZnO) single crystal was implanted by arsenic ions with fluence of 1014cm?2 at room temperature followed by post-implantation annealing up to 900°C. Rectifying property was not observed in the As-implanted or the post-implantation annealed samples. Au Schottky contact was fabricated on the samples with the H2O2 pre-treatment. Deep-level transient spectroscopy measurements were performed on the

C. Y. Zhu; C. C. Ling; G. Brauer; W. Anwand; W. Skorupa

2009-01-01

9

Deep level transient spectroscopic study of oxygen-implanted ZnO single crystal  

Microsoft Academic Search

ZnO single crystal samples were implanted by oxygen with the energy of 150keV. After the pretreatment of hydrogen peroxide [1], Schottky contacts were fabricated with Au film deposited by thermal evaporation. Deep level defects were studied by deep level transient spectroscopy (DLTS). The activation energy of the 0.29eV deep trap was observed in the as-implanted sample and samples anneal at

Ziran Ye; Guangwei Ding; Jincheng Fan; Chi Chung Ling

2011-01-01

10

Electrical and photoluminescence properties of carbon implanted ZnO bulk single crystals  

NASA Astrophysics Data System (ADS)

Carbon-ions, which are expected as an amphoteric impurity, are implanted into ZnO bulk single crystals with a fluence of 1.5 × 10 15 cm -2. The carbon-ion implanted ZnO shows the n-type conductivity and the resistivity varies from 6 × 10 4 ? cm (for unimplanted samples) to 3 × 10 -2 ? cm (for 800 °C-annealed ones). The Rutherford backscattering (RBS) studies show the existence of the displaced zinc atoms. In photoluminescence (PL) measurements, the broad emission at 2.34 eV observed in un-implanted and as-implanted samples is related to oxygen vacancy and zinc interstitial. After annealing, the weak PL-emission related to carbon donor is observed at 3.06 eV, indicating that the donor level lies at ˜310 meV below the conduction band. The carbon-ion implanted ZnO layer with the low resistivity achieved in the present study suggests the possibility of transparent conductive oxide.

Matsumoto, K.; Kuriyama, K.; Kushida, K.

2009-05-01

11

Defects in 6 MeV H+ irradiated hydrothermal ZnO single crystal.  

PubMed

The effect of 6 MeV H(+) irradiation on hydrothermally grown ZnO single crystal has been investigated using high resolution x-ray diffraction (HRXRD) and optical absorption (ultraviolet-visible) spectroscopy. The increase of the diffuse scattering in the reciprocal space maps measured using HRXRD indicates an increase of the point defect density upon irradiation. Within the penetration depth of x-rays of several micrometres, the defect density increased with increasing distance from the sample surface. On the other hand, the near band gap optical absorption became sharper for the irradiated crystal. This reflects enhanced band to band absorption and reduced sub-band gap absorption due to defects. Temperature dependent photoluminescence spectra of the pristine sample show negative thermal quenching (NTQ) of the luminescence which is due to the presence of two or more donor related defects. Upon irradiation, a single dominant donor bound transition can be found without any temperature induced NTQ. Enhancement of the band edge luminescence and reduction of the defect related luminescence is observed at 10 K. Such changes have been discussed in the light of the hydrogen present in the as-grown state of hydrothermal ZnO. PMID:23988867

Sarkar, A; Chakrabarti, Mahuya; Bhowmick, D; Chakrabarti, A; Ray, S K; Rafaja, D; Sanyal, D

2013-09-25

12

Coherent scattering of exciton polaritons and acoustic phonons in a ZnO single crystal  

NASA Astrophysics Data System (ADS)

The light reflection oscillations resulting from the coherent scattering of polariton states and propagating coherent acoustic phonons (CAPs) in a ZnO single crystal are studied by using a two-color femtosecond pump-probe technique. The oscillation frequency manifested in the photoinduced reflectance shows a nonlinear dependence on the probe-beam wave vector owing to the variation of the refractive index near the band gap. The oscillation amplitude is affected by the refractive index modulation derived from the CAP-detuning polariton states. The larger oscillation for shorter probe-beam wavelengths is consistent with the stronger scattering between the CAP and excitonlike polariton states closer to the band gap.

Liu, Wenhui; Xie, Wei; Guo, Wenping; Xu, Dan; Hu, Tao; Ma, Tianping; Yuan, Haochen; Wu, Yizheng; Zhao, Haibin; Shen, Xuechu; Chen, Zhanghai

2014-05-01

13

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

14

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

15

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

NASA Astrophysics Data System (ADS)

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; Wolverson, Daniel; Sebald, Kathrin; Hodges, Chris; Kuball, Martin; Voss, Tobias

2013-05-01

16

Surface characterization of Cu-ion implanted single crystal and thin film ZnO for catalytic applications  

Microsoft Academic Search

Single crystals and thin films of zinc oxide were implanted with copper ions in order to study the catalytic properties of a mixed Cu-ZnO system. ZnO is widely used as a catalyst in the methanol synthesis reaction, and copper has been noted to have a synergistic effect on the rates and yields of reaction. The samples were characterized by x-ray

J. S. Brodkin; D. Chadwick

1995-01-01

17

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

18

[Photoluminescence of one dimension ZnO single crystal columns array excited by different space variation direction].  

PubMed

Highly-oriented single crystal ZnO columns array was prepared by a simple two-step evaporation oxidation method. And the photoluminescence properties of different direction excitation were investigated. Upon different direction excitation, the emission spectra were greatly different. Besides the relative intensity of different emission peak of PL changed; some new emission peaks werealso detected at high excitation power. This showed that the energy absorption, transmission and emission in one dimension ZnO column array were directional. The up-conversion polarized photoluminescence spectra were also found, and the intensities of 400 nm emission peak were affected by the laser polarization orientation. These results showed that the intensity and shape of PL were related with the direction and polarization of the excitation laser. The results also give some important references for subminiature one dimension line array optoelectric device. PMID:16201355

Xie, Ping-bo; Zhao, Fu-li; Li, Ya-dong; Gong, Zhen; Wang, He-zhou

2005-06-01

19

Evaluation of Melt-Grown, ZnO Single Crystals for Use as Alpha-Particle Detectors  

SciTech Connect

As part of an ongoing investigation of the scintillation properties of zinc-oxide-based scintillators, several melt-grown, ZnO single crystals have been characterized using -particle excitation, infrared reflectance, and room temperature photoluminescence. The crystals, grown by Cermet, Inc. using a pressurized melt growth process, were doped with Group 1 elements (Li), Group 2 elements (Mg), Group 3 elements (Ga, In) and Lanthanides (Gd, Er, Tm). The goals of these studies are to better understand the scintillation mechanisms associated with various members of the ZnO scintillator family and to then use this knowledge to improve the radiation detection capabilities of ZnO-based scintillators. One application for which ZnO is particularly well suited as a scintillator is as the associated particle detector in a deuterium-tritium (D-T) neutron generator. Application requirements include the exclusion of organic materials, outstanding timing resolution, and high radiation resistance. ZnO(Ga) and ZnO(In) have demonstrated fast (sub-nanosecond) decay times with relatively low light yields, and ZnO(Ga) has been used in a powder form as the associated particle detector for a D-T neutron generator. Four promising candidate materials, ZnO, ZnO:Ga, ZnO:In,Li, and ZnO:Er,Li, were identified in this study. These four samples demonstrated sub-nanosecond decay times and alpha particle excited luminescence comparable to BC-400 fast plastic scintillator. The ZnO:Mg,Ga, ZnO:Gd, and ZnO:Li samples demonstrated appreciable slow (microsecond) decay components that would be incompatible with high-counting-rate applications.

Neal, John S [ORNL; Giles, N. C. [West Virginia University; Yang, Xiaocheng [West Virginia University; Wall, R. Andrew [Wake Forest University, Winston-Salem, NC; Ucer, Burak [Wake Forest University, Winston-Salem, NC; Williams, Richard T. [Wake Forest University, Winston-Salem, NC; Wisniewski, Dariusz J [ORNL; Boatner, Lynn A [ORNL; Rengarajan, Varatharajan [ORNL; Nause, Jeff E [ORNL; Nemeth, Bell [Cermet, Inc., Atlanta

2008-01-01

20

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

21

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

22

Persistent photoconductivity and photo-responsible defect in 30 MeV-electron irradiated single crystal ZnO  

SciTech Connect

Persistent photoconductivity (PPC) in 30-MeV electron irradiated ZnO single crystals is studied by excitation using light emitting diodes (LEDs) with various wavelengths. The decay transient of the photoconductivity shows relaxation times in the range of a few ten days for the illumination at 90 K and a few hours at room temperature. An electron paramagnetic resonance (EPR) signal with g-value = 2.005 appears after illumination of blue LED, suggesting the transfer from the artificially introduced oxygen vacancy of 2+ charge state to the metastable + charge state. Once generated, the metastable state does not immediately decay into the 2+ charge state because of energetic barriers of approx190 meV, supporting the mechanism of PPC proposed by Van de Walle.

Kuriyama, K.; Matsumoto, K. [College of Engineering and Research Center of Ion Beam Technology, Hosei University, Koganei, Tokyo 184-8584 (Japan); Kushida, K. [Dept. of Arts and Sciences, Osaka Kyoiku University, Kashiwara, Osaka 582-8582 (Japan); Xu, Q. [Research Reactor Institute, Kyoto University, Kumatori, Osaka 540-04 (Japan)

2010-01-04

23

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

NASA Astrophysics Data System (ADS)

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 ˜103 ?cm for un-implanted samples to ˜10-2 ?cm for as-implanted ones are observed. The resistivity is further decreased to ˜10-3 ?cm by annealing. The origins of the low resistivity are attributed to both the zinc interstitial (Zni) 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.; Kushida, K.

2013-12-01

24

Gallium doping dependence of single-crystal n-type Zno grown by metal organic chemical vapor deposition  

NASA Astrophysics Data System (ADS)

High-quality single-crystal Ga-doped ZnO films have been epitaxially deposited on (0 0 0 2) sapphire substrate by low-pressure metal organic chemical vapor deposition (MOCVD) technique. The dependence of structural, electrical and optical properties of films on Ga doping concentration was investigated. As grown at the Ga/Zn gas ratio of 3.2 at%, the film shows a narrow linewidth of 0.26° for ZnO (0 0 0 2) peak, high carrier concentration of 2.47×10 19 cm -3, and high optical transparency over 90%. The carrier concentration increased sharply and became saturated at higher doping level due to the onset of carrier compensation. The Burstein-Moss blueshift of the absorption edge energy increased as expected with the carrier concentration up to 2.47×10 19 cm -3. In addition, doping-induced photoluminescence (PL) emission linewidth broadening and bandgap renormalization (BGR) effects have also been observed. The intensity of PL emission decreased with increasing Ga dopant concentration, which was believed to be a direct consequence of the doping-enhanced nonradiative recombination rates.

Ye, J. D.; Gu, S. L.; Zhu, S. M.; Liu, S. M.; Zheng, Y. D.; Zhang, R.; Shi, Y.; Yu, H. Q.; Ye, Y. D.

2005-10-01

25

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

26

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

27

Vertically Aligned Single-Crystal ZnO Nanotubes Grown on ?-LiAlO2(100) Substrate by Metalorganic Chemical Vapor Deposition  

NASA Astrophysics Data System (ADS)

Vertically aligned single-crystal ZnO nanotubes were grown on a ?-LiAlO2(100) substrate by metalorganic chemical vapor deposition (MOCVD) under proper growth conditions. The diameter of these nanotubes varies from 15 to 100 nm and their wall thickness is in the range of 5-30 nm. Photoluminescence measurements indicate that these nanotubes have enhanced green emission due to a much improved surface area, which is predominant over the near-band edge emission. The synthesis of ZnO nanotubes provides a new route and a new material system for forming nanostructures such as a quantum ring.

Zhang, Guoqiang; Adachi, Masahiko; Ganjil, Sandip; Nakamura, Atsushi; Temmyo, Jiro; Matsui, Yoshio

2007-08-01

28

Study of the local environment diversity between Co- and Mn-doped ZnO single crystal film by multilayer growth technique  

NASA Astrophysics Data System (ADS)

We investigated the room temperature ferromagnetism and their local coordination environment of Co and Mn doped in ZnO single crystal films. Both films show room temperature ferromagnetism and the saturated magnetization of the Mn-doped ZnO film is stronger than that of the Co-doped films. From the analysis on the local structures of Zn, Co, and Mn, we verify that the lattice distortions mainly surround the Co and Mn dopants. Due likely to the relatively large cation size, the Mn dopant would induce a greater local lattice distortion. We suggest that the local environment disorder between the Co and Mn dopants may play a role to the origin of ZnO based diluted magnetic semiconductor films.

Huang, J. C. A.; Hsu, H. S.; Sun, J. H.; Chiu, S. L.; Lee, C. H.; Liao, Y. F.; Chou, H.

2008-04-01

29

Valence-band-ordering of a strain-free bulk ZnO single crystal identified by four-wave-mixing spectroscopy technique  

NASA Astrophysics Data System (ADS)

Spectroscopic and temporal four-wave-mixing (FWM) measurements are carried out on a strain-free bulk ZnO single crystal, in order to clarify the valence-band-ordering. Under the collinearly polarized lights with the electric-field component parallel to the c-axis, which can excite dipole-allowed ?1-excitons, the FWM signal appears only in the energies corresponding to the B-exciton. Under the cross-linear polarization configuration exciting both ?5- and ?1-excitons, the FWM signal arising from the two-photon-coherence is absent in the energies corresponding to A-exciton. Both the results indicate that ?1-exciton state belongs exclusively to B-exciton, meaning that the valence-band ordering is ?9-?7-?7 in order of decreasing electron energy for the present strain-free ZnO single crystal.

Hazu, K.; Chichibu, S. F.; Adachi, S.; Sota, T.

2012-05-01

30

Persistent Photoconductivity in electron-irradiated ZnO bulk single crystals: Evaluation of the metastable conductive state by the dual light illumination  

NASA Astrophysics Data System (ADS)

Persistent Photoconductivity (PPC) in 30 MeV electron-irradiated n-type ZnO single crystals is studied under the dual light illumination (DLI: the infrared light excitation after the blue illumination). Below 160 K, the remarkable reduction in PPC is observed by the subsequent infrared illumination, suggesting the release of electrons from the perturbed-host state (PHS) as a metastable conductive state to the nonconductive state ( VO+ and/or VO0) via the higher unoccupied states inside the conduction band. Above 160 K, the slight increase in photocurrent is observed by the subsequent illumination, suggesting the photoexcitation of electrons not relevant to the PHS. These results depend on the electron concentration in the PHS.

Oga, T.; Izawa, Y.; Kuriyama, K.; Kushida, K.; Xu, Q.

2011-11-01

31

Characterization of the lattice defects in Ge-ion implanted ZnO bulk single crystals by Rutherford Backscattering: Origins of low resistivity  

NASA Astrophysics Data System (ADS)

A Ge ion implantation using a multiple-step energy into ZnO bulk single crystals is performed (net concentration: 2.6 × 1020 cm-3). The origins of low resistivity of the Ge implanted ZnO samples are studied by Rutherford backscattering spectroscopy (RBS), photoluminescence (PL). The resistivity measured by Van der Pauw method decreases from ˜103 ?cm for the un-implanted samples to 1.45 × 10-2 ?cm for the as-implanted samples, originating from the lattice displacement of Zn (Zni) (˜30 meV [Look et al., Phys. Rev. Lett. 82, 2552 (1999)]), the existence of which is revealed by the RBS measurements. In contrast, the 1000 °C annealed samples show the higher resistivity of 6.26 × 10-1 ?cm, indicating that the Zni related defects decrease but still remain despite the annealing. A new PL emission appears at around 372 nm (3.33 eV) in the annealed samples, suggesting a Ge donor with an activation energy of 100 meV. This value corresponds to the activation energy (102 meV) of a Ge donor estimated from the temperature dependence of carrier concentration. These results suggest that the resistivity in the 1000 °C annealed samples results from both the Zni related defects and the electrically activated Ge donor.

Kamioka, K.; Oga, T.; Izawa, Y.; Kuriyama, K.; Kushida, K.

2013-07-01

32

Site-specific interaction of H 2O with ZnO single-crystal surfaces studied by thermal desorption and UV photoelectron spectroscopy  

NASA Astrophysics Data System (ADS)

The adsorption and condensation of H 2O(D 2O) on ZnO(101¯0), (0001)Zn and (0001¯)O surfaces was investigated by means of thermal desorption (TDS) and UV photoelectron spectroscopy (UPS). The clean ZnO single-crystal surfaces were prepared by Ar-ion sputtering and annealing and characterised by Auger electron spectroscopy, LEED, UPS and work-function measurements. On all three surfaces six different adsorption states were found. In the monolayer regime there is a stronger bonding to Zn sites (desorption temperature 340 K) than to O sites (190 K), The bonding to the Zn sites seems to be accompanied by some clustering. Before the chemisorption layer is completed a first ice state is found whose desorption temperature shifts from 162 to 168 K with increasing exposures. At higher exposures the multilayer ice state is found at 152 K. On the (0001¯)O face defect-induced features were identified. The water lone-pair orbital 1b 1, whose energy falls between the O p and the Zn 3d emission of the substrate and which is known to show bonding shifts, was analysed using angle-resolved UPS. In the monolayer, the main chemisorption states are found at EBV(1b 1) = -9.6 eV for the (0001)Zn face and at - 10.6 eV for the (0001¯)O face and are compared with the multilayer ice emission at 1¯1.1 eV. The difference in binding energies shows the same trend as the TDS data. For the (101¯0) face the 1b 1 emission is very broad, indicating some overlap between different states.

Zwicker, G.; Jacobi, K.

1983-08-01

33

Lasing characteristics of optically-pumped single ZnO micro/nanocrystal  

NASA Astrophysics Data System (ADS)

Zinc oxide (ZnO) has a wide band-gap energy of 3.37 eV and a large exciton binding energy of 60 meV which is considerably larger than the thermal energy at room temperature (26 meV), and therefore, efficient exciton emission in ultraviolet (UV) region can be expected. Especially, ZnO micro/nanocrystals are quite attractive as building blocks for efficient UV opto-electronic devices. We have been investigating micro-cavity UV lasing from variously-shaped ZnO micro/nanocrystals, and micro-cavity lasing from ZnO nanowire and nanosheet have been confirmed, so far. Recently, we could fabricate ZnO micro/nanosphere crystals by a simple laser ablation method of ZnO sintered target in the air. In this study, we report UV micro-cavity lasing from an optically-pumped single ZnO micro/nanosphere crystal, for the first time. The spherical-micro-cavity lasing characteristics were investigated and discussed by comparisons with theoretical considerations in terms of quality factor and mode spacing of its lasing spectra with modal structures. From those considerations, it was found that the lasing mechanisms within a ZnO sphere crystal was attributed to whispering-gallery- mode (WGM) cavity lasing, and a ZnO sphere crystal had a good light confinement property due to the internal total reflections. Since the fabrication method is very simple and productive without any time-consuming crystal-growth process, ZnO micro/nanosphere crystals can be promising building blocks for UV opto-electronic devices such as a UV laser diode. In addition, since a ZnO micro/nanosphere can operate as an active WGM refractometric sensor for small molecules in UV region, high sensitivity enhanced by high quality factor, refractive index, and wavelength dispersion can be expected.

Okazaki, Kota; Shimogaki, Tetsuya; Fusazaki, Koshi; Higashihata, Mitsuhiro; Nakamura, Daisuke; Koshizaki, Naoto; Okada, Tatsuo

2013-03-01

34

Deposition of thin film ZnO with characteristics close to bulk crystal ZnO  

Microsoft Academic Search

Excellent films of piezoelectric ZnO with characteristics close to bulk crystal ZnO have been reliably deposited by rf planar magnetron sputtering. The successful deposition has resulted from the optimization of the sputtering process parameters, such as substrate temperature, gas pressure, target power density, etc. The c-axis orientation of the films has been tested with normal scans and rocking curves of

Abhijeet Sathe; Eun Sok Kim

1994-01-01

35

Single crystal magnets  

NASA Astrophysics Data System (ADS)

Single crystals of the Fe-Cr-Co alloys without and with 3% Mo were prepared by a recrystallization process. The microstructures and the magnetic properties of <100>, <110>, and <111> single crystals were investigated after the heat treatment in the ridge region of the miscibility gap. The magnetic properties of the Fe-22 Cr-17 Co ridge single crystals were not affected very much by the crystal orientation. However, the Fe-23 Cr-20 Co-3 Mo alloys show the crystal orientation dependence of the magnetic properties. The single crystal alloys are aged in a magnetic field, the direction of which is varied around <100> axes. The magnetic properties are measured parallel to the applied field directions and are summarized in view of deviated angle from a <100> axis. The greater the deviation of the applied field direction from a <100> axis, the poorer are the magnetic properties of the Mo single crystal alloy. The best magnetic properties are achieved with Fe-22 Cr-18.5 Co-3 Mo <100> ridge single crystal as Br=1.58 T (15.8 kG), bHc=72.8 kA/m (910 Oe), and (BH)max=91.2 kJ/m3 (11.4 MGOe), which is the highest energy product reported for the Fe-Cr-Co magnet family.

Ikuta, N.; Okada, M.; Homma, M.; Minowa, T.

1983-09-01

36

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

37

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

38

Controlled growth of vertically aligned ZnO nanowires with different crystal orientation of the ZnO seed layer  

Microsoft Academic Search

A novel synthesis and growth method achieving vertically aligned zinc oxide (ZnO) nanowires on a silicon dioxide (SiO2) coated silicon (Si) substrate is demonstrated. The growth direction of the ZnO nanowires is determined by the crystal structure of the ZnO seed layer, which is formed by the oxidation of a DC-sputtered Zn film. The [002] crystal direction of the seed

S N Cha; B G Song; J E Jang; J E Jung; I T Han; J H Ha; J P Hong; D J Kang; J M Kim

2008-01-01

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

Single-crystal gallium nitride nanotubes  

NASA Astrophysics Data System (ADS)

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 by using carbon nanotubes and porous membranes as templates, or by thin-film rolling. These nanotubes, however, are either amorphous, polycrystalline or exist only in ultrahigh vacuum. The growth of single-crystal semiconductor hollow nanotubes would be advantageous in potential nanoscale electronics, optoelectronics and biochemical-sensing applications. Here we report an `epitaxial casting' approach for the synthesis of single-crystal GaN nanotubes with inner diameters of 30-200nm and wall thicknesses of 5-50nm. Hexagonal ZnO nanowires were used as templates for the epitaxial overgrowth of thin GaN layers in a chemical vapour deposition system. The ZnO nanowire templates were subsequently removed by thermal reduction and evaporation, resulting in ordered arrays of GaN nanotubes on the substrates. This templating process should be applicable to many other semiconductor systems.

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

2003-04-01

41

Single photon emission from ZnO nanoparticles  

NASA Astrophysics Data System (ADS)

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; Johnson, Brett C.; Castelletto, Stefania; Ton-That, Cuong; Phillips, Matthew R.; Aharonovich, Igor

2014-06-01

42

Controlled growth of vertically aligned ZnO nanowires with different crystal orientation of the ZnO seed layer  

NASA Astrophysics Data System (ADS)

A novel synthesis and growth method achieving vertically aligned zinc oxide (ZnO) nanowires on a silicon dioxide (SiO2) coated silicon (Si) substrate is demonstrated. The growth direction of the ZnO nanowires is determined by the crystal structure of the ZnO seed layer, which is formed by the oxidation of a DC-sputtered Zn film. The [002] crystal direction of the seed layer is dominant under optimized thickness of the Zn film and thermal treatment. Vertically aligned ZnO nanowires on SiO2 coated Si substrate are realized from the appropriately thick oxidized Zn seed layer by a vapor-solid growth mechanism by catalyst-free thermal chemical vapor deposition (CVD). These experimental results raise the possibility of using the nanowires as functional blocks for high-density integration systems and/or photonic applications.

Cha, S. N.; Song, B. G.; Jang, J. E.; Jung, J. E.; Han, I. T.; Ha, J. H.; Hong, J. P.; Kang, D. J.; Kim, J. M.

2008-06-01

43

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

44

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

45

Crystal orientation control of polycrystalline TiN thin films using ZnO under layers deposited by magnetron sputtering  

Microsoft Academic Search

The effect of ZnO under layers on crystal growth of TiN thin films was investigated. TiN single layers and double-layered ZnO\\/TiN thin films were deposited on soda-lime-silicate glass substrates by magnetron sputtering. XRD analysis indicated that TiN single layers exhibited {111} preferred orientation on glass substrates; on the other hand, the TiN thin films with {100} preferred orientation were obtained

Kazuhiro Kato; Hideo Omoto; Atsushi Takamatsu; Takao Tomioka

2011-01-01

46

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

47

Experimental and theoretical study of CO adsorption on the surface of single phase hexagonally plate ZnO  

NASA Astrophysics Data System (ADS)

A simple low temperature hydrothermal method has been investigated for synthesis of single phase hexagonally plate ZnO microstructure. The synthesized ZnO was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) photoluminescence spectrum (PL) and ultraviolet and visible absorption spectroscopy (UV-vis) to investigate the surface morphology, crystallographic phase, optical properties and used as a sensor for detection of CO gas molecules. It was observed that the ZnO microstructures were uniform size, single phase and symmetrical, with a hexagonal shape and height of ?250 nm. The optical band gap value of this sample was calculated to be about 3.22 eV, which show a red shift with theoretical method. High-resolution TEM images indicate that all the microstructures are single crystals with a [0 0 1] direction growth. We studied the gas response of this sample to 500 ppm CO over a temperature range of 200-400 °C and compared with theoretical results. Density functional theory (DFT) calculations were employed to investigate the structure and electronic properties of ZnO with simulating the adsorption process of CO gas on the ZnO (1 0 1) surface. The theoretical results were in good agreement with experimental results.

Akbari, Amin; Firooz, Azam Anaraki; Beheshtian, Javad; Khodadadi, Abbas Ali

2014-10-01

48

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

NASA Astrophysics Data System (ADS)

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 ZnO nanoparticles and 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 of ˜560-720 nm and typically exhibits two broad spectral peaks separated by ˜150 meV. The excited state lifetimes range from 1 to 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.

Jungwirth, N. R.; Pai, Y. Y.; Chang, H. S.; MacQuarrie, E. R.; Nguyen, K. X.; Fuchs, G. D.

2014-07-01

49

Preparation of vertically aligned ZnO crystal rods in aqueous solution at external electric field  

NASA Astrophysics Data System (ADS)

In this study, an external electric field was used to facilitate the growth of vertically aligned ZnO crystal rods on the surface of indium tin oxide (ITO) glass substrates in an aqueous solution. We used Zn(NO3) and C6H12N4 as precursor and reagent. We found that the external electric field generated by DC potential of 5 kV between two electrodes that were placed outside the bottle could facilitate the growth of homogeneous, high density and vertically aligned ZnO crystal rods. Position of the substrate during the growth of crystal was found to be important to obtain well aligned crystal. The crystals that were grown near the negative electrode had the best properties. Photoluminescence measurement at room temperature revealed sharp peaks at around 360 and 380 nm and a broad peak around 420 nm that indicated good properties of ZnO crystals grown with external electric field.

Prijamboedi, B.; Maryanti, E.; Haryati, T.

2014-06-01

50

Optical nonlinear investigations on morphology controlled growth of ZnO crystals  

NASA Astrophysics Data System (ADS)

We report a methodical study about the third order optical nonlinearity of anisotropic growth of ZnO crystals embedded in polymeric matrices and nanowires on the glass substrate with the use of pre-existing textured ZnO, ZnS and TiO2 seeds using a Z-scan method with Nd:YAG laser (532 nm, 7 ns, 10 Hz). The studies show that the optical nonlinearity of ZnO crystals is highly dependent on the structural geometry and the correlation of semiconductor. Our study offers better insights into the third-order nonlinear optical characteristics of ZnO crystals and reveals great potential for applications in nonlinear photonic devices.

Thankappan, Aparna; Linslal, C. L.; Divya, S.; Sabitha, P. V.; Thomas, Sheenu; Nampoori, V. P. N.

2014-12-01

51

Development of single crystal membranes  

NASA Technical Reports Server (NTRS)

The design and construction of a high pressure crystal growth chamber was accomplished which would allow the growth of crystals under inert gas pressures of 2 MN/sq m (300 psi). A novel crystal growth technique called EFG was used to grow tubes and rods of the hollandite compounds, BaMgTi7O16, K2MgTi7O16, and tubes of sodium beta-alumina, sodium magnesium-alumina, and potassium beta-alumina. Rods and tubes grown are characterized using metallographic and X-ray diffraction techniques. The hollandite compounds are found to be two or three-phase, composed of coarse grained orientated crystallites. Single crystal c-axis tubes of sodium beta-alumina were grown from melts containing excess sodium oxide. Additional experiments demonstrated that crystals of magnesia doped beta-alumina and potassium beta-alumina also can be achieved by this EFG technique.

Stormont, R. W.; Cocks, F. H.

1972-01-01

52

Growth of Single- and Bilayer ZnO on Au(111) and Interaction with Copper  

SciTech Connect

The stoichiometric single- and bi-layer ZnO(0001) have been prepared by reactive deposition of Zn on Au(111) and studied in detail with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory calculations. Both single- and bi-layer ZnO(0001) adopt a planar, graphite-like structure similar to freestanding ZnO(0001) due to the weak van der Waals interactions dominating their adhesion with the Au(111) substrate. At higher temperature, the single-layer ZnO(0001) converts gradually to bi-layer ZnO(0001) due to the twice stronger interaction between two ZnO layers than the interfacial adhesion of ZnO with Au substrate. It is found that Cu atoms on the surface of bi-layer ZnO(0001) are mobile with a diffusion barrier of 0.31 eV, and likely to agglomerate and form nanosized particles at low coverages; while Cu atoms tend to penetrate a single layer of ZnO(0001) with a barrier of 0.10 eV, resulting in a Cu free surface.

Deng, Xingyi; Yao, Kun; Sun, Keju; Li, Wei-Xue; Lee, Junseok; Matranga, Christopher

2013-05-30

53

A simple method for systematically controlling ZnO crystal size and growth orientation  

SciTech Connect

We present a simple, easy and reproducible method to systematically control the dimension and shape evolution of zinc oxide (ZnO) as thin film on glass substrate by chemical bath deposition (CBD). The only varying factor to control crystal transformation is the molar ratio of Cd{sup 2+}/Zn{sup 2+}, R{sub m}, in the initial chemical solution. With the increase of R{sub m}, ZnO crystals transformed from long-and-slim hexagonal rods to fat-and-short hexagonal pyramids, and then to twinning hexagonal dots as observed by scanning electron microscopy (SEM). Film crystallinity was characterized by X-ray diffraction (XRD). Chemical component analysis by energy dispersive spectroscopy (EDS) showed that most cadmium was present in the residual solution instead of the developed film and the precipitate at the bottom of beaker. The mechanism of the cadmium effect, with different initial concentrations, on ZnO crystal transformation was tentatively addressed. We believe that cadmium influences the chelate ligands adsorption onto (0001-bar) plane of ZnO crystals, alters the crystal growth orientation, and thus directs the transformation of the size and shape of ZnO crystals.

Zhang Rong [Department of Paper and Chemical Engineering, Miami University, Oxford, OH 45056 (United States); Kerr, Lei L. [Department of Paper and Chemical Engineering, Miami University, Oxford, OH 45056 (United States)], E-mail: kerrll@muohio.edu

2007-03-15

54

Hydrothermal synthesis and gas sensing properties of single-crystalline ultralong ZnO nanowires  

Microsoft Academic Search

Ultralong ZnO nanowires were successfully synthesized by a simple hydrothermal reaction of Zn foil and aqueous Na2C2O4 solution at 140°C. The as-synthesized ZnO nanowires are single crystalline with the wurtzite structure and grow in the [0001]\\u000a direction. The role of Na2C2O4 in the formation of ultralong ZnO nanowires was investigated, and a possible mechanism was also proposed to account for

Li Li; Heqing Yang; Hua Zhao; Jie Yu; Junhu Ma; Lijuan An; Xuewen Wang

2010-01-01

55

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 templates using a low-temperature atomic layer deposition process. The polystyrene is removed by firing spectrum. Material infiltration of three-dimensional 3D colloidal crystals has been shown to be a versatile

Cao, Hui

56

Growth of ZnO nanolayers inside the capillaries of photonic crystal fibres  

E-print Network

In this study, we describe the formation of ZnO nanolayers inside the air capillaries of a silica photonic crystal fibre (PCF), targeting random laser and organic vapor sensing applications. ZnO nanolayers were developed by infiltrating the capillaries of the silica PCF with Zn-acetate/methanol solutions of various concentrations, followed by annealing treatments. The growth and morphology of the synthesized ZnO nanolayers were characterized by means of scanning electron microscopy (SEM) and found to be affected by the concentration of the Zn-acetate/methanol infiltration solution. For low concentrations, inspection with SEM revealed the formation of 25 and 100-nm-thick ZnO nanolayers across the entire length of the infiltrated capillaries, whereas increasing the Zn-acetate concentration resulted to the formation of randomly placed isolated ZnO nanorods. Room temperature photoluminescence spectra of the ZnO nanolayers inside the PCF were measured and compared with the corresponding spectra reported for ZnO st...

Konidakis, I; Zito, G; Pissadakis, S

2013-01-01

57

Melt growth of ZnO bulk crystals in Ir crucibles  

NASA Astrophysics Data System (ADS)

The growth of ZnO bulk crystals from the melt is difficult due to the high melting point of the material ( Tm = 1975 °C), requiring the use of Ir crucibles, and its thermal decomposition upon heating. A thermodynamic analysis shows that the oxygen partial pressure in the surrounding vapour phase should be as low as possible during the heating cycle at lower temperatures in order to avoid the oxidation of Ir to IrO 2. Approaching the ZnO melting point, however, higher oxygen pressure is required for suppressing the ZnO decomposition, while IrO 2 decomposes in the elements. The required increasing oxygen supply with increasing temperature can be accomplished by the addition of CO 2 to the gas atmosphere. Experimental results prove the correctness of these results. In a Bridgman-like process ZnO boules are obtained that consist of a few large grains with cm dimensions.

Jacobs, Klaus; Schulz, Detlev; Klimm, Detlef; Ganschow, Steffen

2010-03-01

58

Nanoscale Calorimetry of Isolated Polyethylene Single Crystals  

E-print Network

Nanoscale Calorimetry of Isolated Polyethylene Single Crystals A. T. KWAN, M. YU. EFREMOV, E. A-film differential scanning calorimetry to investigate the melt- ing of isolated polyethylene single crystals: microelectromechanical systems; calorimetry; nanocalorimetry; polyeth- ylene single crystals; melting INTRODUCTION We

Allen, Leslie H.

59

Photon tunnelling microscopy of polyethylene single crystals  

E-print Network

Photon tunnelling microscopy of polyethylene single crystals Mohan Srinivasarao* and Richard S polyethylenesinglecrystals, providing a topographical map ofthe single-crystal surface.Tunnelling increases exponentially:photon tunnellingmicroscopy;single crystals; polyethylene) INTRODUCTION The study of morphology of polymers is an area

Srinivasarao, Mohan

60

Zn(O, S) layers for chalcoyprite solar cells sputtered from a single target  

NASA Astrophysics Data System (ADS)

A simplified Cu(In, Ga)(S, Se)2/Zn(O, S)/ZnO:Al stack for chalcopyrite thin-film solar cells is proposed. In this stack the Zn(O, S) layer combines the roles of the traditional CdS buffer and undoped ZnO layers. It will be shown that Zn(O, S) films can be sputtered in argon atmosphere from a single mixed target without substrate heating. The photovoltaic performance of the simplified stack matches that of the conventional approach. Replacing the ZnO target with a ZnO/ZnS target may therefore be sufficient to omit the CdS buffer layer and avoid the associated complexity, safety and recycling issues, and to lower production cost.

Grimm, A.; Kieven, D.; Lauermann, I.; Lux-Steiner, M. Ch.; Hergert, F.; Schwieger, R.; Klenk, R.

2012-09-01

61

Large-Scale Hexagonal-Patterned Growth of Aligned ZnO Nanorods for  

E-print Network

experiments was 895 nm. For deposition, a 1 cm Ã? 1 cm single-crystal sapphire (21h1h0) substrate was sonicated vapor-liquid-solid (VLS) growth on a single crystal alumina substrate. The ZnO nanorods have uniform main steps. The hexagonally patterned ZnO nanorod arrays are grown onto a single-crystal Al2O3

Wang, Zhong L.

62

Growth of epitaxial ZnO thin films on lattice-matched buffer layer: Application of InGaO 3(ZnO) 6 single-crystalline thin film  

Microsoft Academic Search

Effects of lattice-matched substrates on growth of ZnO epitaxial films were studied. ZnO thin films were grown on single-crystalline InGaO3(ZnO)6 (IGZO) layers, which have small lattice mismatches of ?0.8% and ?2.2% in a- and c-axes, respectively. Epitaxial ZnO films were grown with the epitaxial relationship between the ZnO film and the single-crystalline IGZO of [0001]ZnO\\/\\/[0001]IGZO\\/\\/[111]YSZ and [112¯0]ZnO\\/\\/[112¯0]IGZO\\/\\/[11¯0]YSZ. The use of

Yujiro Takeda; Kenji Nomura; Hiromichi Ohta; Hiroshi Yanagi; Toshio Kamiya; Masahiro Hirano; Hideo Hosono

2005-01-01

63

Titania single crystals with a curved surface.  

PubMed

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. PMID:25373513

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

2014-01-01

64

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

65

Broadband ZnO Single-Nanowire Light-Emitting Diode  

E-print Network

on a thin film of nanowires.5,6 ZnO is a large band-gap (Eg ) 3.35 eV at 300 K)7 semiconductor, with several in bulk or thin films.15-17 Our technique (Figure 1) relies on the use of poly(methyl methacrylate) (PMMABroadband ZnO Single-Nanowire Light-Emitting Diode Jiming Bao, Mariano A. Zimmler, and Federico

Bao, Jiming

66

Growth of single crystal diamond  

NASA Astrophysics Data System (ADS)

The subject of the research presented in this dissertation is the growth of single crystal diamond by microwave plasma chemical vapor deposition (CVD). Both heteroepitaxial and homoepitaxial growth methods have been examined, with emphasis on producing large diamond crystals of high structural and chemical perfection. By heteroepitaxy, epitaxial growth on a foreign substrate, diamond was grown on (001) Ir thin-film epitaxial buffer layers deposited on (001) strontium titanate (SrTiO3) by DC magnetron sputtering. To nucleate diamond on Ir, the Ir surface was bombarded with low energy ions extracted from the hydrocarbon plasma, a process known as DC biasing or bias-enhanced nucleation. Since this critical process is poorly understood, attention was paid to the spatial and temporal evolution of the Ir surface during the bias treatment. It was discovered that the biased Ir surface is etched on a surprisingly short time scale during which highly correlated nanopillars, 3-4 nm in height with mean separation 15 nm, emerge. The etching process is spatially non-uniform, propagating from substrate center to substrate edge in minutes. Diamond grew on Ir without an intervening phase. Lattice images revealed that interfacial strain from the 7% Ir-diamond lattice mismatch is largely relieved by misfit dislocations within 1 nm of the interface. It is suggested that the high nucleation density obtained with specific bias conditions is associated with the roughened Ir surface. To grow heteroepitaxial diamond as thick films, a two-step growth method was explored. This process involved the transfer of a thin heteroepitaxial diamond film, still attached to a substrate, to a second reactor where high growth rate conditions were possible. Characterization of films grown by this approach showed that the resulting diamond had much lower levels of internal strain, suggesting that the process could be used to grow diamond crystals of structural quality similar to natural diamond. In homoepitaxy, epitaxial growth on a substrate of the same material, diamond was deposited by CVD directly onto high-pressure, high-temperature Type Ib diamond substrates. Methods for removing substrate surface damage, as well as other imperfections, were devised by use of plasma etching. The characteristics and statistics of pits formed during etching were studied. Diamond growth methods were developed with the aim of minimizing the formation of various structural and chemical defects. To accomplish this, several growth parameters were varied, including substrate temperature, feed gas concentration, growth rate, substrate surface, microwave power, and reactor geometry. Regions of parameter space were found in which the diamond (001) surface remained smooth during growth, and complete suppression of instabilities that create hillocks or non-epitaxial crystallites was demonstrated. A great deal of information was obtained by interrupting growth, removing the crystal from the reactor for optical inspection, and then resuming the process with no apparent negative effects. Diamond crystals were grown on 3 x 3 mm2 substrates with thicknesses greater than 0.5 mm. The chemical purity of the crystals was such that it was impossible to observe signatures of substitutional nitrogen at the ppm level.

Regmi, Murari

67

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

68

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

69

Ames Lab 101: Single Crystal Growth  

SciTech Connect

Ames Laboratory scientist Deborah Schlagel talks about the Lab's research in growing single crystals of various metals and alloys. The single crystal samples are vital to researchers' understanding of the characteristics of a materials and what gives these materials their particular properties.

Schlagel, Deborah

2013-09-27

70

Ames Lab 101: Single Crystal Growth  

ScienceCinema

Ames Laboratory scientist Deborah Schlagel talks about the Lab's research in growing single crystals of various metals and alloys. The single crystal samples are vital to researchers' understanding of the characteristics of a materials and what gives these materials their particular properties.

Schlagel, Deborah

2014-06-04

71

Single crystals for welding research  

SciTech Connect

Most welds last for many years, but a few fail after a relatively short time. Knowing the reasons why welds fail is important because cracks in welds can threaten the safety of people in buildings, airplanes, ships, automobiles, and power plants. Bad welds can lead to costly, extended shutdowns of industrial facilities such as petroleum refineries. Thus, research on this very important fabrication technology is critical to the multibillion-dollar welding industry. Research at ORNL and elsewhere strives to determine the structural features that make some welds strong and others weak. The goals are to find cost-effective ways to characterize the structure and strength of a new weld, correctly predict whether it will last a long time, and determine the welding conditions most likely to produce high-quality welds. There is more to welding than meets the eye. The cracks that make welds fail result from the complexities of microstructures formed during welding. Thus weld microstructure is linked to weld properties such as mechanical strength. As the hot weld material cools from a liquid into a solid, the crystalline grains grow at different speeds and in different directions, forming a new microstructure. By using single crystals rather than polycrystalline alloys to study different weld microstructures, scientists at ORNL have developed a way to predict more accurately the microstructures of various welds. The results could guide welders in providing the right conditions (correct welding speed, heat input, and weld thickness) for producing safer, higher-quality, and longer-lasting welds.

David, S.A.; Boatner, L.A.

1991-01-01

72

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

73

Single Crystal Sapphire Optical Fiber Sensor Instrumentation  

SciTech Connect

The goal of this 30 month program is to develop reliable accurate temperature sensors based on single crystal sapphire materials that can withstand the temperatures and corrosive agents present within the gasifier environment. The research for this reporting period has been segregated into two parallel paths--corrosion resistance measurements for single crystal sapphire fibers and investigation of single crystal sapphire sensor configurations. The ultimate goal of this phase one segment is to design, develop and demonstrate on a laboratory scale a suitable temperature measurement device that can be field tested in phase two of the program.

Anbo Wang; Russell May; Gary R. Pickrell

2000-10-28

74

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

75

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

76

Electrical Properties of Black Phosphorus Single Crystals  

Microsoft Academic Search

Large single crystals of black phosphorus have been grown under high pressure, and by using the crystals, the Hall measurements have been done in a range from 4.2 K to 550 K. All the undoped samples have exhibited p-type conduction, while we have succeeded in obtaining n-type crystals by doping Te impurity. The effective acceptor concentrations NA-ND of the p-type

Yuichi Akahama; Shoichi Endo; Shin-ichiro Narita

1983-01-01

77

Sublimation Kinetics of Zinc Single Crystals.  

National Technical Information Service (NTIS)

The kinetics of the free surface sublimation of zinc single crystals were investigated using the torsion-Langmuir technique in conjunction with optical and electron microscopes. Sublimation from cleaved surfaces took place in two distinct stages, a stage ...

R. W. Mar

1968-01-01

78

Anisotropic Third-Order Optical Nonlinearity of a single ZnO Micro/Nanowire  

E-print Network

the anisotropic third-order optical nonlinearity of a single ZnO micro/nanowire by using the Z-scan method-infrared region using the Z-scan method with a femtosecond laser (800 nm, 50 fs). The TPA and NLR as a function. The Z-scan method is used to determine the anisot

Wang, Zhong L.

79

Influence of crystal orientation on ECAP of aluminum single crystals  

Microsoft Academic Search

A single crystal of high purity aluminum, oriented with the {111} slip plane and the ?110? slip direction rotated by 20° in a clockwise sense from the theoretical shear plane and the shear direction, was processed by equal-channel angular pressing (ECAP) through a single pass. This configuration was designated the 20° orientation and the results are compared with earlier data

Yukihide Fukuda; Keiichiro Oh-ishi; Minoru Furukawa; Zenji Horita; Terence G. Langdon

2006-01-01

80

Synthesis of PS colloidal crystal templates and ordered ZnO porous thin films by dip-drawing method  

Microsoft Academic Search

Polystyrene spheres (PS) were synthesized by an emulsifier-free emulsion polymerization technique and the PS colloidal crystal templates were assembled orderly on clean glass substrates by dip-drawing method from emulsion of PS. Porous ZnO thin films were prepared by filling the ZnO sol into the spaces among the close-packed PS templates and then annealing to remove the PS templates. The effects

Zhifeng Liu; Zhengguo Jin; Wei Li; Jijun Qiu; Juan Zhao; Xiaoxin Liu

2006-01-01

81

Flux growth of ZnO crystals doped by transition metals  

NASA Astrophysics Data System (ADS)

ZnO crystals doped with Cr, Mn, Fe and Co were grown by the flux method. The prepared crystals revealed no phase separation detectable by X-ray diffraction. Structure properties were characterized by Raman and photoluminescence spectroscopy. For ZnO:Co, Mn and Cr, no spontaneous ferromagnetic moment was observed up to T=2 K whereas for the ZnO:Fe crystals the m( H) curves suggest the existence of 5 nm superparamagnetic iron clusters. At low temperatures the m( H) curves can be interpreted as a superposition of major paramagnetic and minor antiferromagnetic contribution. The paramagnetic part corresponds to the presence of Co 2+, Fe 3+, Mn 2+ ions and small Cr atom clusters.

Sofer, Zden?k; Sedmidubský, David; Huber, Št?pán; Hejtmánek, Ji?í; Maryško, Miroslav; Jurek, Karel; Mikulics, Martin

2011-01-01

82

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

83

Growth mechanism of ZnO deposited by nitrogen mediated crystallization  

NASA Astrophysics Data System (ADS)

We investigate the growth mechanism of ZnO deposited by a nitrogen mediated crystallization (NMC) method. NMC is a method in which nitrogen is used to control nucleation via a nitrogen adsorption–desorption behavior. The growth of NMC-ZnO is classified into three stages, that is, the pre-nucleation stage, nucleation and grain growth stage for 4–30 nm in thickness, and coalescence stage for 31–100 nm in thickness. NMC-ZnO nucleation takes place in a very short period compared to that for conventional ZnO. Hence, NMC-ZnO has a uniform grain size distribution, flat surface with less spiky grains, and a longer lateral correlation length of the surface, leading to a larger grain size than in conventional ZnO. Utilizing this NMC-ZnO as a buffer layer, low resistive aluminum doped zinc oxide ZnO:Al (AZO) films are obtained at the buffer layer film thickness ranging from 4 to 30 nm. The lowest resistivity is 3.4 × 10−4 Ω cm for 90 nm thick AZO deposited on NMC-ZnO buffer layers of 10 and 30 nm in thickness.

Suhariadi, Iping; Shiratani, Masaharu; Itagaki, Naho

2014-09-01

84

Oxygen Incorporation in Rubrene Single Crystals  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

85

Remarkable structural diversity and single-crystal-to-single-crystal transformations in sulfone functionalized lanthanide MOFs  

SciTech Connect

We report the formation of novel open framework lanthanide (La, Ce, Pr and Dy) MOFs using the ligand 4,4{prime}-bibenzoic acid-2,2{prime}-sulfone. In the case of Ce and Pr, an unprecedented single-crystal-to-single-crystal transformation at room temperature was discovered.

Neofotistou, Eleftheria; Malliakas, Christos D.; Trikalitis, Pantelis N. (NWU); (Crete)

2010-04-13

86

Helical Single Crystals Grown in Confined Space  

NASA Astrophysics Data System (ADS)

We report here the formation and growth process of the double-twist PET(R*-9) helical single crystals. It has been observed that the population of helical crystals increases with increasing the thickness of the thin films. In addition to the crystallization temperature effect, the pitch lengths along both the long and short twist axes also change with thin film thickness, which is attributed to the substrate confinement effect on the thin film samples. The early stage of the helical crystals has been studied using solvent washing experiments. It has been found that the morphology is a saddle-like shape. Nucleation starts at the center of the flat-on part, and growth directions include both along the long and short axes of the crystals. Coexistence of the flat-elongated and helical forms will also be discussed.

Li, Christopher; Cheng, Stephen; Zhang, John; Harris, Frank; Chien, Liang-Chy; Lotz, Bernard

2001-03-01

87

Photoluminescence quenching in oligothiophene single crystal  

Microsoft Academic Search

A single crystal of stereo-regularly substituted dihexylsexithiophene (DH6T) was synthesized. The transient photoluminescence decay curve of the crystal was non-exponential as in amorphous polythiophene. This non-exponential decay curve could be successfully described by stretched exponential decay kinetics, which represent the exciton diffusing to the one-dimensionally dispersed quenching centers. The generation of radical species by photoirradiation was confirmed by light-induced ESR

Tadatake Sato; Mamoru Fujitsuka; Motoo Shiro; Kazuyoshi Tanaka

1998-01-01

88

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

89

ZnO field-effect transistors prepared by aqueous solution-growth ZnO crystal thin film  

NASA Astrophysics Data System (ADS)

A ZnO thin-film transistor (TFT) with a channel layer formed via aqueous solution-growth at low temperature is demonstrated. This ZnO thin-film semiconductor has a well-controlled crystalline form, exhibiting n-channel, enhancement-mode behavior with a channel mobility as large as 0.56 cm2 V-1 s-1. Low-cost, superior transistor characteristics and low-temperature processing makes ZnO TFT attractive for flexible electronics on temperature sensitive substrates.

Li, Chensha; Li, Yuning; Wu, Yiliang; Ong, Beng S.; Loutfy, Rafik O.

2007-10-01

90

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

91

Charge transport in single crystal organic semiconductors  

NASA Astrophysics Data System (ADS)

Organic electronics have engendered substantial interest in printable, flexible and large-area applications thanks to their low fabrication cost per unit area, chemical versatility and solution processability. Nevertheless, fundamental understanding of device physics and charge transport in organic semiconductors lag somewhat behind, partially due to ubiquitous defects and impurities in technologically useful organic thin films, formed either by vacuum deposition or solution process. In this context, single-crystalline organic semiconductors, or organic single crystals, have therefore provided the ideal system for transport studies. Organic single crystals are characterized by their high chemical purity and outstanding structural perfection, leading to significantly improved electrical properties compared with their thin-film counterparts. Importantly, the surfaces of the crystals are molecularly flat, an ideal condition for building field-effect transistors (FETs). Progress in organic single crystal FETs (SC-FETs) is tremendous during the past decade. Large mobilities ~ 1 - 10 cm2V-1s-1 have been achieved in several crystals, allowing a wide range of electrical, optical, mechanical, structural, and theoretical studies. Several challenges still remain, however, which are the motivation of this thesis. The first challenge is to delineate the crystal structure/electrical property relationship for development of high-performance organic semiconductors. This thesis demonstrates a full spectrum of studies spanning from chemical synthesis, single crystal structure determination, quantum-chemical calculation, SC-OFET fabrication, electrical measurement, photoelectron spectroscopy characterization and extensive device optimization in a series of new rubrene derivatives, motivated by the fact that rubrene is a benchmark semiconductor with record hole mobility ~ 20 cm2V-1s-1. With successful preservation of beneficial pi-stacking structures, these rubrene derivatives form high-quality single crystals and exhibit large ambipolar mobilities. Nevertheless, a gap remains between the theory-predicted properties and this preliminary result, which itself is another fundamental challenge. This is further addressed by appropriate device optimization, and in particular, contact engineering approach to improve the charge injection efficiencies. The outcome is not only the achievement of new record ambipolar mobilities in one of the derivatives, namely, 4.8 cm2V-1s-1 for holes and 4.2 cm2V-1s-1 for electrons, but also provides a comprehensive and rational pathway towards the realization of high-performance organic semiconductors. Efforts to achieve high mobility in other organic single crystals are also presented. The second challenge is tuning the transition of electronic ground states, i.e., semiconducting, metallic and superconducting, in organic single crystals. Despite an active research area since four decades ago, we aim to employ the electrostatic approach instead of chemical doping for reversible and systematic control of charge densities within the same crystal. The key material in this study is the high-capacitance electrolyte, such as ionic liquids (ILs), whose specific capacitance reaches ~ ?F/cm2, thus allowing accumulation of charge carrier above 1013 cm-2 when novel transport phenomena, such as insulator-metal transition and superconductivity, are likely to occur. This thesis addresses the electrical characterization, device physics and transport physics in electrolyte-gated single crystals, in the device architecture known as the electrical double layer transistor (EDLT). A detailed characterization scheme is first demonstrated for accurate determination of several key parameters, e.g., carrier mobility and charge density, in organic EDLTs. Further studies, combining both experiments and theories, are devoted to understanding the unusual charge density dependent channel conductivity and gate-to-channel capacitance behaviors. In addition, Hall effect and temperature-dependent measurements are employed for more in-depth unders

Xie, Wei

92

Synthesis and characterization of single-phase Mn-doped ZnO  

Microsoft Academic Search

Different samples of Zn1?xMnxO series have been prepared using conventional solid-state sintering method. We identified up to what extent doping will enable us to synthesize single-phase polycrystalline Mn-doped ZnO sample, which is one of the prerequisites for dilute magnetic semiconductor, and we have analyzed its some other physical aspects. In synthesizing the samples, proportion of Mn varies from 1 to

S. Chattopadhyay; S. Dutta; Aritra Banerjee; D. Jana; S. Bandyopadhyay; A. Sarkar

2009-01-01

93

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

NASA Astrophysics Data System (ADS)

An epitaxially aligned ZnO nano-seed layer was used to improve the microstructure and crystal alignment in metalorganic chemical vapor deposited ZnO films on Al 2O 3 (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 shows an irregular, leaf-like surface morphology with a large surface roughness. Moreover, its crystal alignment is random. In sharp contrast, a fairly smooth surface is observed for the ZnO film grown with the seed layer. In addition, the film shows an epitaxially aligned nature. Our results suggest that the insertion of the nano-seed layer be an effective way to grow well-oriented, smooth ZnO films.

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

2005-03-01

94

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

95

Growth of single-crystal gallium nitride  

NASA Technical Reports Server (NTRS)

Use of ultrahigh purity ammonia prevents oxygen contamination of GaN during growth, making it possible to grow the GaN at temperatures as high as 825 degrees C, at which point single crystal wafers are deposited on /0001/-oriented sapphire surfaces.

Clough, R.; Richman, D.; Tietjen, J.

1970-01-01

96

Magnetic Properties of Single Crystal Nickel Nanowires  

NASA Astrophysics Data System (ADS)

Toward the goal of understanding magnetism in confined dimensions, we have synthesized Nickel nanowires (NWs) by chemical vapor deposition and characterized their magnetic properties. By tuning chemical vapor deposition synthesis parameters, we can controllably synthesize a variety of morphologically dissimilar Ni products onto untreated amorphous SiO2||Si substrates [1]. These structures include polycrystalline core-shell NWs, single-crystal cubes, in-plane wires, and vertically-oriented single crystal arrays. To probe the magnetic properties of individual NWs, we combined magneto-transport, XPEEM, and magnetic modeling. For polycrystalline NWs, the magnetic properties are dominated by shape anisotropy. However, for single-crystal NWs, there is a competition between the shape anisotropy along the (001) direction and magneto-crystalline anisotropy along the (111) direction. This gives rise to complex magnetic stripe domain patterns along the wires, interesting magneto-transport properties, and novel reversal modes not typically observed in magnetic wires. [4pt] [1] K.T. Chan, J.J. Kan, E.E. Fullerton, et al., "Oriented Growth of Single-Crystal Ni Nanowires onto Amorphous SiO2," Nano Letters, Oct. 2010

Kan, Jimmy; Chan, Keith; Shipton, Erik; Fullerton, Eric

2011-03-01

97

Stress Corrosion cracking of copper single crystals  

Microsoft Academic Search

Constant extension rate tests have been carried out on copper single crystals in a sodium nitrite solution, using an applied potential to accelerate the cracking. Crack velocities up to 30 nm per second were obtained at 30 °C. The stress-corrosion fracture surfaces are cleavage-like, with curved striations parallel to the crack front. If the dynamic straining is stopped, the cracks

K. Sieradzki; R. L. Sabatini; R. C. Newman

1984-01-01

98

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

99

Crystal ion slicing of single-crystal magnetic garnet films  

Microsoft Academic Search

Epitaxial liftoff has been used for achieving heterogeneous integration of many III-V and elemental semiconductor systems. However, it has been heretofore impossible to integrate devices of many other important material systems. A good example of this problem has been the integration of single-crystal transition metal oxides on semiconductor platforms, a system needed for on-chip thin film optical isolators. We report

M. Levy; R. M. Osgood; A. Kumar; H. Bakhru

1998-01-01

100

Single ZnO nanowire-PZT optothermal field effect transistors.  

PubMed

A new type of pyroelectric field effect transistor based on a composite consisting of single zinc oxide nanowire and lead zirconate titanate (ZnO NW-PZT) has been developed. Under infrared (IR) laser illumination, the transconductance of the ZnO NW can be modulated by optothermal gating. The drain current can be increased or decreased by IR illumination depending on the polarization orientation of the Pb(Zr(0.3)Ti(0.7))O(3) (PZT) substrate. Furthermore, by combining the photocurrent behavior in the UV range and the optothermal gating effect in the IR range, the wide spectrum of response of current by light offers a variety of opportunities for nanoscale optoelectronic devices. PMID:22895012

Hsieh, Chun-Yi; Lu, Meng-Lin; Chen, Ju-Ying; Chen, Yung-Ting; Chen, Yang-Fang; Shih, Wan Y; Shih, Wei-Heng

2012-09-01

101

Single ZnO nanowire-PZT optothermal field effect transistors  

NASA Astrophysics Data System (ADS)

A new type of pyroelectric field effect transistor based on a composite consisting of single zinc oxide nanowire and lead zirconate titanate (ZnO NW-PZT) has been developed. Under infrared (IR) laser illumination, the transconductance of the ZnO NW can be modulated by optothermal gating. The drain current can be increased or decreased by IR illumination depending on the polarization orientation of the Pb(Zr0.3Ti0.7)O3 (PZT) substrate. Furthermore, by combining the photocurrent behavior in the UV range and the optothermal gating effect in the IR range, the wide spectrum of response of current by light offers a variety of opportunities for nanoscale optoelectronic devices.

Hsieh, Chun-Yi; Lu, Meng-Lin; Chen, Ju-Ying; Chen, Yung-Ting; Chen, Yang-Fang; Shih, Wan Y.; Shih, Wei-Heng

2012-09-01

102

Experimental Investigation of Orthoenstatite Single Crystal Rheology  

NASA Astrophysics Data System (ADS)

The plasticity of enstatite, upper mantle second most abundant mineral, is still poorly constrained, mostly because of its high-temperature (T) transformation into proto- and clino-enstatite at low pressure (P). Mackwell (1991, GRL, 18, 2027) reports a pioneer study of protoenstatite (Pbcn) single-crystal rheology, but the results do not directly apply to the orthorhombic (Pbca) mantle phase. Ohuchi et al. (2011, Contri. Mineral. Petrol , 161, 961) carried out deformation experiments at P=1.3 GPa on oriented orthoenstatite crystals, investigating the activity of [001](100) and [001](010) dislocation slip systems; they report the first rheological laws for orthoenstatite crystals. However, strain and stress were indirectly constrained in their experiments, which questioned whether steady state conditions of deformation were achieved. Also, data reported for [001](100) slip system were obtained after specimens had transformed by twinning into clinoenstatite. We report here new data from deformation experiments carried out at high T and P ranging from 3.5 to 6.2 GPa on natural Fe-bearing enstatite single crystals, using the Deformation-DIA apparatus (D-DIA) that equipped the X17B2 beamline of the NSLS (NY, USA). The applied stress and specimen strain rates were measured in situ by X-ray diffraction and imaging techniques (e.g., Raterron & Merkel, 2009, J. Sync. Rad., 16, 748; Raterron et al., 2013, Rev. Sci. Instr., 84, 043906). Three specimen orientations were tested: i) with the compression direction along [101]c crystallographic direction, which forms a 45° angle with both [100] and [001] axes, to investigate [001](100) slip-system activity; ii) along [011]c direction to investigate [001](010) system activity; iii) and along enstatite [125] axis, to activate both slip systems together. Crystals were deformed two by two, to compare slip system activities, or against enstatite aggregates or orientated olivine crystals of known rheology for comparison. Run products microstructures were investigated by transmission electron microscopy. Despite a significant hardening with P, enstatite [001](100) slip system is found to be the easiest system at mantle P and T. Furthermore, orthoenstatite crystals exhibit a higher sensitivity to stress than olivine crystals, i.e. a higher n exponent in classical power laws. At the low stress level prevailing in the Earth mantle, enstatite crystals are thus harder than olivine crystals.

fraysse, G.; Girard, J.; Holyoke, C. W.; Raterron, P.

2013-12-01

103

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

104

The Creep of Single Crystals of Aluminum  

NASA Technical Reports Server (NTRS)

The creep of single crystals of high-purity aluminum was investigated in the range of temperatures from room temperature to 400 F and at resolved-shear-stress levels of 200, 300, and 400 psi. The tests were designed in an attempt to produce data regarding the relation between the rate of strain and the mechanism of deformation. The creep data are analyzed in terms of shear strain rate and the results are discussed with regard to existing creep theories. Stress-strain curves were determined for the crystals in tinsel and constant-load-rate tests in the same temperature range to supplement the study of plastic deformation by creep with information regarding the part played by crystal orientation, differences in strain markings, and other variables in plastic deformation.

Johnson, R D; Shober, F R; Schwope, A D

1953-01-01

105

Transverse acoustic actuation of Ni-Mn-Ga single crystals  

E-print Network

Two methods for the transverse acoustic actuation of {110}-cut Ni-Mn-Ga single crystals are discussed. In this actuation mode, crystals are used that have the {110}- type twinning planes parallel to the base of the crystal. ...

Simon, Jesse Matthew

2007-01-01

106

Ferromagnetic Resonance of Single-Crystal Gadolinium  

Microsoft Academic Search

Gadolinium metal is a system of relative simplicity as far as exchange interactions and ionic states are concerned. The 8S7?2 state of Gd3+ is consistent with the observed 7?b?atom and the moment contributing f electrons are most likely exchange coupled via conduction electrons. The present work concerns the measurement of the ferromagnetic resonance behavior of a single crystal at frequencies

T. W. Moore; D. S. Rodbell

1964-01-01

107

Amplified spontaneous emission in quaterthiophene single crystals  

Microsoft Academic Search

The authors demonstrate amplified spontaneous emission (ASE) from quaterthiophene single crystals and study its behavior at low temperature. The room temperature photoluminescence exhibits line narrowing (spectral width down to 10 nm) at 553 nm for excitation fluence larger than 1 mJ cm-2. At low temperature (10 K), ASE is observed from two vibronic transitions at 510 nm (0-1) and 553

Marco Polo; Andrea Camposeo; Silvia Tavazzi; Luisa Raimondo; Peter Spearman; Antonio Papagni; Roberto Cingolani; Dario Pisignano

2008-01-01

108

Stress Corrosion cracking of copper single crystals  

Microsoft Academic Search

Constant extension rate tests have been carried out on copper single crystals in a sodium nitrite solution, using an applied\\u000a potential to accelerate the cracking. Crack velocities up to 30 nm per second were obtained at 30 ?C. The stress-corrosion\\u000a fracture surfaces are cleavage-like, with curved striations parallel to the crack front. If the dynamic straining is stopped,\\u000a the cracks

K. Sieradzki; R. L. Sabatini; R. C. Newman

1984-01-01

109

Single crystal diamond detector for radiotherapy  

NASA Astrophysics Data System (ADS)

The new generation of synthetic diamonds grown as a CVD single crystal on a high pressure high temperature substrate offers a wide range of applications. In particular, because of the near tissue equivalence and its small size (good spatial resolution), CVD single crystal diamond finds applicability in radiotherapy as a dosemeter of ionizing radiation. In this paper we report the electrical and dosimetric properties of a new diamond detector which was fabricated at IFJ based on a single crystal detector-grade CVD diamond provided with a novel contact metallization. Diamond properties were assessed at IFJ using a Theratron 680E therapeutic 60Co gamma rays unit and at COOK with 6 and 18 MV x-rays Varian Clinac CL2300 C/D accelerator. The new dosemeter showed high electric and dosimetric performances: low value of dark current, high current at the level of some nanoamperes during irradiation, very fast dynamic response with a rise time amounting to parts of a second, good stability and repeatability of the current and linearity of the detector signal at different dose and dose rate levels typically applied in radiotherapy. The results confirm the potential applicability of diamond material as a dosemeter for applications in radiotherapy.

Schirru, F.; Kisielewicz, K.; Nowak, T.; Marczewska, B.

2010-07-01

110

Property-performance control of multidimensional, hierarchical, single-crystalline ZnO nanoarchitectures.  

PubMed

Diverse morphologies of multidimensional hierarchical single-crystalline ZnO nanoarchitectures including nanoflowers, nanobelts, and nanowires are obtained by use of a simple thermal evaporation and vapour-phase transport deposition technique by placing Au-coated silicon substrates in different positions inside a furnace at process temperatures as low as 550 °C. The nucleation and growth of ZnO nanostructures are governed by the vapour-solid mechanism, as opposed to the commonly reported vapour-liquid-solid mechanism, when gold is used in the process. The morphological, structural, compositional and optical properties of the synthesized ZnO nanostructures can be effectively tailored by means of the experimental parameters, and these properties are closely related to the local growth temperature and gas-phase supersaturation at the sample position. In particular, room-temperature photoluminescence measurements reveal an intense near-band-edge ultraviolet emission at about 386 nm for nanobelts and nanoflowers, which suggests that these nanostructures are of sufficient quality for applications in, for example, optoelectronic devices. PMID:22407732

Cheng, Qijin; Ostrikov, Kostya Ken

2012-04-23

111

A nanoporous two-dimensional polymer by single-crystal-to-single-crystal photopolymerization  

NASA Astrophysics Data System (ADS)

In contrast to the wide number and variety of available synthetic routes to conventional linear polymers, the synthesis of two-dimensional polymers and unambiguous proof of their structure remains a challenge. Two-dimensional polymers—single-layered polymers that form a tiling network in exactly two dimensions—have potential for use in nanoporous membranes and other applications. Here, we report the preparation of a fluorinated hydrocarbon two-dimensional polymer that can be exfoliated into single sheets, and its characterization by high-resolution single-crystal X-ray diffraction analysis. The procedure involves three steps: preorganization in a lamellar crystal of a rigid monomer bearing three photoreactive arms, photopolymerization of the crystalline monomers by [4?+?4] cycloaddition, and isolation of individual two-dimensional polymer sheets. This polymer is a molecularly thin (~1?nm) material that combines precisely defined monodisperse pores of ~9?Å with a high pore density of 3.3?×?1013 pores?cm-2. Atomic-resolution single-crystal X-ray structures of the monomer, an intermediate dimer and the final crystalline two-dimensional polymer were obtained and prove the single-crystal-to-single-crystal nature and molecular precision of the two-dimensional photopolymerization.

Kissel, Patrick; Murray, Daniel J.; Wulftange, William J.; Catalano, Vincent J.; King, Benjamin T.

2014-09-01

112

A nanoporous two-dimensional polymer by single-crystal-to-single-crystal photopolymerization.  

PubMed

In contrast to the wide number and variety of available synthetic routes to conventional linear polymers, the synthesis of two-dimensional polymers and unambiguous proof of their structure remains a challenge. Two-dimensional polymers-single-layered polymers that form a tiling network in exactly two dimensions-have potential for use in nanoporous membranes and other applications. Here, we report the preparation of a fluorinated hydrocarbon two-dimensional polymer that can be exfoliated into single sheets, and its characterization by high-resolution single-crystal X-ray diffraction analysis. The procedure involves three steps: preorganization in a lamellar crystal of a rigid monomer bearing three photoreactive arms, photopolymerization of the crystalline monomers by [4?+?4] cycloaddition, and isolation of individual two-dimensional polymer sheets. This polymer is a molecularly thin (~1?nm) material that combines precisely defined monodisperse pores of ~9?Å with a high pore density of 3.3?×?10(13) pores?cm(-2). Atomic-resolution single-crystal X-ray structures of the monomer, an intermediate dimer and the final crystalline two-dimensional polymer were obtained and prove the single-crystal-to-single-crystal nature and molecular precision of the two-dimensional photopolymerization. PMID:25143211

Kissel, Patrick; Murray, Daniel J; Wulftange, William J; Catalano, Vincent J; King, Benjamin T

2014-09-01

113

Synthesis of PS colloidal crystal templates and ordered ZnO porous thin films by dip-drawing method  

NASA Astrophysics Data System (ADS)

Polystyrene spheres (PS) were synthesized by an emulsifier-free emulsion polymerization technique and the PS colloidal crystal templates were assembled orderly on clean glass substrates by dip-drawing method from emulsion of PS. Porous ZnO thin films were prepared by filling the ZnO sol into the spaces among the close-packed PS templates and then annealing to remove the PS templates. The effects of ZnO precursor sol concentration and dipping time in sol on the porous structure of the thin films were studied. The results showed an ordered ZnO porous thin film with designed pore size that depended on the sol concentration and PS size could be obtained. And the shrinkage of pore diameter was about 30-43%. X-ray diffraction (XRD) spectra indicated the thin film was wurtzite structure. The transmittance spectrum showed that optical transmittance decreased with the decrease of wavelength, but kept above 80% optical transmittances beyond the wavelength of 550 nm. Optical band gap of the porous ZnO thin film (fired at 500 °C) was 3.22 eV.

Liu, Zhifeng; Jin, Zhengguo; Li, Wei; Qiu, Jijun; Zhao, Juan; Liu, Xiaoxin

2006-05-01

114

Chapter III: Catalytic Activation of CO Over Single Crystals  

E-print Network

1 Chapter III: Catalytic Activation of CO Over Single Crystals José A. Rodriguez and D. Wayne Introduction III.2 Methanation of CO on Single Crystal Surfaces III.2.1 CO methanation on clean metal single crystals. III.2.1.1 Monometallic surfaces A. Ni(100) and Ni(111) B. Ru(110) and Ru(001) C. W(110) D. Rh(111

Goodman, Wayne

115

Comprehensive study of the surface morphology evolution induced by thermal annealing in single-crystalline ZnO Films and ZnO bulks  

NASA Astrophysics Data System (ADS)

We report on the evolution of the surface morphology induced by thermal annealing in N2 ambient over a wide temperature range of 500-1200 °C in single-crystalline ZnO films and ZnO bulks. The surface morphology is seriously changed by the annealing temperature, and the evolution can be categorized into three regions: island growth, island agglomeration, and pit formation. Island growth at low temperatures below 700 °C, is ascribed to the atomic migration to reduce surface energy, which causes surface roughening. Island agglomeration at intermediate temperatures of 700-900 °C is ascribed to the migration and the evaporation of surface atoms, which causes surface flattening. Pit formation at high temperatures above 900 °C is ascribed to the atomic evaporation by high vapor pressure, which causes surface destruction. On the other hand, the bulk lattice is continuously improved with increasing annealing temperature in the temperature regions before the surface-destruction region, which is attributed to the reduction in the numbers of point and line defects caused by recrystallization. As a result, the best surface morphology and the best bulk lattice are obtained at an annealing temperature of 900 °C. The common surface-morphology evolution of ZnO films and ZnO bulks with increasing annealing temperature can be summarized using the three steps of surface roughening by island growth, surface flattening by island agglomeration, and surface destruction by pit formation.

Yoon, N.; Oh, D. C.; Ko, H. J.; Lim, D. S.; Hong, S. K.; Yao, T.

2012-11-01

116

Crystal ion slicing of single-crystal magnetic garnet films  

NASA Astrophysics Data System (ADS)

Epitaxial liftoff has been used for achieving heterogeneous integration of many III-V and elemental semiconductor systems. However, it has been heretofore impossible to integrate devices of many other important material systems. A good example of this problem has been the integration of single-crystal transition metal oxides on semiconductor platforms, a system needed for on-chip thin film optical isolators. We report here an implementation of epitaxial liftoff in magnetic garnets. Deep ion implantation is used to create a buried sacrificial layer in single-crystal yttrium iron garnet (YIG) and bismuth-substituted YIG (Bi-YIG) epitaxial layers grown on gadolinium gallium garnet (GGG). The damage generated by the implantation induces a large etch selectivity between the sacrificial layer and the rest of the garnet. Ten-micron-thick films have been lifted off from the original GGG substrates by etching in phosphoric acid. Millimeter-size pieces of excellent quality have been transferred to the silicon and gallium arsenide substrates. Study of the magnetic domain structure in the detached epilayers by Faraday contrast shows no changes in film anisotropy. Optical insertion loss measurements are also presented.

Levy, M.; Osgood, R. M.; Kumar, A.; Bakhru, H.

1998-06-01

117

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

118

Selective area growth of well-ordered ZnO nanowire arrays with controllable polarity.  

PubMed

Controlling the polarity of ZnO nanowires in addition to the uniformity of their structural morphology in terms of position, vertical alignment, length, diameter, and period is still a technological and fundamental challenge for real-world device integration. In order to tackle this issue, we specifically combine the selective area growth on prepatterned polar c-plane ZnO single crystals using electron-beam lithography, with the chemical bath deposition. The formation of ZnO nanowires with a highly controlled structural morphology and a high optical quality is demonstrated over large surface areas on both polar c-plane ZnO single crystals. Importantly, the polarity of ZnO nanowires can be switched from O- to Zn-polar, depending on the polarity of prepatterned ZnO single crystals. This indicates that no fundamental limitations prevent ZnO nanowires from being O- or Zn-polar. In contrast to their catalyst-free growth by vapor-phase deposition techniques, the possibility to control the polarity of ZnO nanowires grown in solution is remarkable, further showing the strong interest in the chemical bath deposition and hydrothermal techniques. The single O- and Zn-polar ZnO nanowires additionally exhibit distinctive cathodoluminescence spectra. To a broader extent, these findings open the way to the ultimate fabrication of well-organized heterostructures made from ZnO nanowires, which can act as building blocks in a large number of electronic, optoelectronic, and photovoltaic devices. PMID:24720628

Consonni, Vincent; Sarigiannidou, Eirini; Appert, Estelle; Bocheux, Amandine; Guillemin, Sophie; Donatini, Fabrice; Robin, Ivan-Christophe; Kioseoglou, Joseph; Robaut, Florence

2014-05-27

119

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

120

Single phase formation of Co-implanted ZnO thin films by swift heavy ion irradiation: Optical studies  

SciTech Connect

Low temperature photoluminescence and optical absorption studies on 200 MeV Ag{sup +15} ion irradiated Co-implanted ZnO thin films were studied. The Co clusters present in as implanted samples were observed to be dissolved using 200 MeV Ag{sup +15} ion irradiation with a fluence of 1x10{sup 12} ions/cm{sup 2}. The photoluminescence spectrum of pure ZnO thin film was characterized by the I{sub 4} peak due to the neutral donor bound excitons and the broad green emission. The Co-doped ZnO films show three sharp levels and two shoulders corresponding to 3t{sub 2g} and 2e{sub g} levels of crystal field splitted Co d orbitals, respectively. The ultraviolet-visible absorption spectroscopy also shows the systematic variation of band gap after 200 MeV Ag{sup +15} ion irradiation.

Kumar, Ravi; Singh, Fouran; Angadi, Basavaraj; Choi, Ji-Won; Choi, Won-Kook; Jeong, Kwangho; Song, Jong-Han; Khan, M. Wasi; Srivastava, J. P.; Kumar, Ajay; Tandon, R. P. [Materials Science Division, Inter-University Accelerator Centre, P.O. Box 10502, Aruna Asaf Ali Marg, New Delhi 110067 (India); Thin Films Materials Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650 (Korea, Republic of); Institute of Physics and Applied Physics, Yonsei University, Shincheon-dong 134, Seoul 120-749 (Korea, Republic of); Advanced Analysis Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650 (Korea, Republic of); Department of Physics, Aligarh Muslim University, Aligarh 202002 (India); Department of Physics and Astrophysics, Delhi University, Delhi 110007 (India)

2006-12-01

121

Thermodynamic forces in single crystals with dislocations  

NASA Astrophysics Data System (ADS)

A simple model for the evolution of macroscopic dislocation regions in a single crystal is presented. This model relies on maximal dissipation principle within Kröner's geometric description of the dislocated crystal. Mathematical methods and tools from shape optimization theory provide equilibrium relations at the dislocation front, similarly to previous work achieved on damage modelling (J Comput Phys 33(16):5010-5044, 2011). The deformation state variable is the incompatible strain as related to the dislocation density tensor by a relation involving the Ricci curvature of the crystal underlying elastic metric. The time evolution of the model variables follows from a novel interpretation of the Einstein-Hilbert flow in terms of dislocation microstructure energy. This flow is interpreted as the dissipation of non-conservative dislocations, due to the climb mechanism, modelled by an average effect of mesoscopic dislocations moving normal to their glide planes by adding or removing points defects. The model equations are a fourth-order tensor parabolic equation involving the operator "incompatibility," here appearing as a tensorial counterpart of the scalar Laplacian. This work encompasses and generalizes results previously announced (C R Acad Sci Paris Ser I 349:923-927, 2011), with in addition a series of physical interpretations to give a meaning to the newly introduced concepts.

Van Goethem, Nicolas

2014-06-01

122

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

123

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

124

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

125

Fabrication of crystals from single metal atoms.  

PubMed

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

126

Constitutive modeling for single crystal superalloys  

NASA Technical Reports Server (NTRS)

The inelastic response of single crystal gamma/gamma prime superalloys is quite different from the behavior of polycrystalline nickel base superalloys. Upto a critical temperature the yield stress of single crystal alloys is a function of the material orientation relative to the direction of the applied stress and the material exhibits significant tension/compression asymmetry. This behavior is primarily due to slip on the octahedral slip system. Above the critical temperature there is a sharp drop in the yield stress, cube slip becomes more predominant and the tension/compression asymmetry is reduced. Similar orientation and tension/compression asymmetry is observed in creep and secondary creep above the critical temperature is inferred to occur by octahedral slip. There are two exceptions to this behavior. First, loading near the (111) orientation exhibits cube slip at all temperatures, and; second, loading near the (001) orientation produces only octahedral slip at all temperatures. The constitutive model is based on separating the total global strain into elastic and inelastic components. This model is developed and briefly discussed.

Stouffer, D. C.; Jayaraman, N.; Sheh, M.; Alden, D.

1986-01-01

127

Polycrystalline ZnO and Mn-doped ZnO nanorod arrays with variable dopant content via a template based synthesis from Zn(II) and Mn(II) Schiff base type single source molecular precursors  

NASA Astrophysics Data System (ADS)

The synthesis and full characterisation of pure and Mn-doped polycrystalline zinc oxide nanorods with tailored dopant content are obtained via a single source molecular precursor approach using two Schiff base type coordination compounds is reported. The infiltration of precursor solutions into the cylindrical pores of a polycarbonate template and their thermal conversion into a ceramic green body followed by dissolution of the template gives the desired ZnO and Mn-doped ZnO nanomaterial as compact rods. The ZnO nanorods have a mean diameter between 170 and 180 nm or 60-70 nm, depending on the template pore size employed, comprising a length of 5-6 ?m. These nanorods are composed of individual sub-5 nm ZnO nanocrystals. Exact doping of these hierarchically structured ZnO nanorods was achieved by introducing Mn(II) into the ZnO host lattice with the precursor complex Diaquo-bis[2-(meth-oxyimino)-propanoato]manganese, which allows to tailor the exact Mn(II) doping content of the ZnO rods. Investigation of the Mn-doped ZnO samples by XRD, TEM, XPS, PL and EPR, reveals that manganese occurs exclusively in its oxidation state + II and is distributed within the volume as well as on the surface of the ZnO host.

Pashchanka, Mikhail; Hoffmann, Rudolf C.; Burghaus, Olaf; Corzilius, Björn; Cherkashinin, Gennady; Schneider, Jörg J.

2011-01-01

128

Employing a cylindrical single crystal in gas-surface dynamics  

Microsoft Academic Search

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

C. Hahn; J. Shan; Y. Liu; O. Berg; A. W. Kleijn; L. B. F. Juurlink

2012-01-01

129

Spatiotemporal growth of faceted and curved single crystals  

PubMed

The spatiotemporal growth of single crystals in a crystalline polymer has been investigated theoretically based on a nonconserved time dependent Ginzburg-Landau equation (known as TDGL model A). In the description of the total free energy, a double-well local free energy density signifying metastability of crystal ordering is combined with a nonlocal free energy term representing an interface gradient. The resulting nonlinear reaction diffusion equation after renormalization possesses a solitary wave property. Two-dimensional numerical calculations were performed to elucidate the faceted single crystal growth including square, rectangular, diamond-shaped, and curved single crystals. A three-dimensional simulation was also undertaken for the emergence of diamond-shaped single crystals in polyethylene. Of particular importance is that the model field parameters can be linked directly to the material parameters of polyethylene single crystals. Simulation with various elements of the interface gradient coefficient tensor captures various topologies of polymer single crystals. PMID:11088211

Kyu; Mehta; Chiu

2000-04-01

130

High-yield synthesis of single-crystalline ZnO hexagonal nanoplates and accounts of their optical and photocatalytic properties  

Microsoft Academic Search

This paper describes a simple hydrothermal procedure for high-yield synthesis of single-crystalline ZnO hexagonal nanoplates in a surfactant-free system at 70 °C. The structures and morphologies of the synthesized ZnO nanoplates are derived from characterisation by X-ray diffraction, and scanning and transmission electron microscopy. Their optical properties are recorded by Raman and photoluminescence spectroscopy. These ZnO hexagonal nanoplates exhibit the

F. Xu; Z.-Y. Yuan; G.-H. Du; M. Halasa; B.-L. Su

2007-01-01

131

High-yield synthesis of single-crystalline ZnO hexagonal nanoplates and accounts of their optical and photocatalytic properties  

Microsoft Academic Search

This paper describes a simple hydrothermal procedure for high-yield synthesis of single-crystalline ZnO hexagonal nanoplates in a surfactant-free system at 70 C. The structures and morphologies of the synthesized ZnO nanoplates are derived from characterisation by X-ray diffraction, and scanning and transmission electron microscopy. Their optical properties are recorded by Raman and photoluminescence spectroscopy. These ZnO hexagonal nanoplates exhibit the enhanced

F. Xu; Z.-Y. Yuan; G.-H. Du; M. Halasa; B.-L. Su

2007-01-01

132

ORIGINAL PAPER Strength of single-crystal orthopyroxene under lithospheric  

E-print Network

ORIGINAL PAPER Strength of single-crystal orthopyroxene under lithospheric conditions Tomohiro sin- gle crystals was investigated via shear deformation exper- iments under lithospheric conditions under the lithospheric conditions suggesting that orthopyroxene may reduce the strength

133

ZnO Channel Waveguides for Nonlinear Optical Applications  

NASA Astrophysics Data System (ADS)

ZnO channel waveguides were fabricated for the first time, for the purpose of being used in nonlinear optical applications. Wide-bandgap ZnO was chosen for the core material to avoid two-photon absorption at wavelengths above 800 nm which are used for biomedical applications. We calculated the single-mode conditions and group-velocity dispersion of the propagating modes for the waveguides. We also fabricated channel waveguides using single-crystal ZnO thin film grown on sapphire substrate. Measured propagation losses with a cut-back method were approximately 3 to 6 dB/mm for single-mode waveguides.

Edgar Yoshio Morales Teraoka,; Tomohiro Kita,; Atsushi Tsukazaki,; Masashi Kawasaki,; Yasuo Ohtera,; Hirohito Yamada,

2010-04-01

134

Experimental dynamic metamorphism of mineral single crystals  

USGS Publications Warehouse

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 u ??rtzite ??? 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 ?? nAl2O3 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. ?? 1993.

Kirby, S. H.; Stern, L. A.

1993-01-01

135

Adsorption of mercaptosilanes on nanocrystalline and single crystal zinc oxide surfaces  

NASA Astrophysics Data System (ADS)

The wide band gap and unique photoluminescence (PL) spectrum of nanocrystalline zinc oxide (nano-ZnO) make it attractive for a variety of photonics and sensor applications. Toward the goal of modifying the electronic structure and optical properties of nano-ZnO, the adsorption of 3-mercaptopropyltriethoxysilane (MPTES) has been investigated. Nano-ZnO rods having widths of 10-20 nm and lengths of 100-300 nm were functionalized by ultrasonicating them in a hot ethanol/water solution and adding MPTES. FTIR and X-ray photoelectron spectroscopy (XPS) of the modified nano- ZnO confirm silane functionalization. The presence of hydroxyl groups prior to functionalization suggests that adsorption to ZnO occurs primarily via a condensation reaction and the formation of Zn-O-Si bonds. Comparison has been made to 3-mercaptopropyltrimethoxysilane (MPTMS) adsorbed in ultrahigh vacuum onto sputter-cleaned single crystal ZnO(0001) in which MPTMS vapor is leaked into the vacuum chamber. In this case, bonding occurs via the thiol groups, as indicated by angle-resolved XPS studies. Similar experiments in which sputter-cleaned ZnO(0001) is dosed with dodecanethiol (DDT) confirm adsorption via S-Zn bond formation. Photoluminescence measurements of MPTES-functionalized nano-ZnO show an increase in intensity of the UV emission peak and a decrease in the visible peak relative to the unfunctionalized particles. The reduction of the visible emission peak is believed to be due to passivation of surface defects.

Singh, Jagdeep; Im, JiSun; Whitten, James E.; Soares, Jason W.; Meehan, Alexa M.; Steeves, Diane M.

2008-08-01

136

ZnO nanodisk based UV detectors with printed electrodes.  

PubMed

The fabrication of highly functional materials for practical devices requires a deep understanding of the association between morphological and structural properties and applications. A controlled hydrothermal method to produce single crystal ZnO hexagonal nanodisks, nanorings, and nanoroses using a mixed solution of zinc sulfate (ZnSO4) and hexamethylenetetramine (HMTA) without the need of catalysts, substrates, or templates at low temperature (75 °C) is introduced. Metal-semiconductor-metal (MSM) ultraviolet (UV) detectors were fabricated based on individual and multiple single-crystal zinc oxide (ZnO) hexagonal nanodisks. High quality single crystal individual nanodisk devices were fabricated with inkjet-printed silver electrodes. The detectors fabricated show record photoresponsivity (3300 A/W) and external quantum efficiency (1.2 × 10(4)), which we attribute to the absence of grain boundaries in the single crystal ZnO nanodisk and the polarity of its exposed surface. PMID:24611747

Alenezi, Mohammad R; Alshammari, Abdullah S; Alzanki, Talal H; Jarowski, Peter; Henley, Simon John; Silva, S Ravi P

2014-04-01

137

Halide electroadsorption on single crystal surfaces  

SciTech Connect

The structure and phase behavior of halides have been investigated on single crystals of Ag and Au using synchrotron x-ray scattering techniques. The adlayer coverages are potential dependent. For all halides studied the authors found that with increasing potential, at a critical potential, a disordered adlayer transforms into an ordered structure. Often these ordered phases are incommensurate and exhibit potential-dependent lateral separations (electrocompression). The authors have analyzed the electrocompression in terms of a model which includes lateral interactions and partial charge. A continuous compression is not observed for Br on Ag(100). Rather, they find that the adsorption is site-specific (lattice gas) in both the ordered and disordered phases. The coverage increases with increasing potential and at a critical potential the disordered phase transforms to a well-ordered commensurate structure.

Ocko, B.M. [Brookhaven National Lab., Upton, NY (United States). Dept. of Physics; Wandlowski, T. [Univ. of Ulm (Germany). Dept. of Electrochemistry

1997-07-01

138

Multiphonon relaxation in YVO4 single crystals  

NASA Astrophysics Data System (ADS)

Multiphonon relaxation rates were measured for 13 different energy levels of various rare-earth ions in YVO4 single crystals at 77 K. Dependence of the multiphonon relaxation rate on the energy gap that separates each emitting multiplet from the one lying just below it was investigated over the range from 980 to 5200 cm-1. A significant change in gap dependence was observed for energy gaps smaller than about 2500 cm-1, in agreement with previous observations and with theoretical investigations. An extreme nonradiative transition rate of 1.1×1011 s-1 (?=9 ps), corresponding to a 980 cm-1 energy gap, was deduced from homogeneous absorption linewidth measurements at 1.5 K.

Ermeneux, F. S.; Goutaudier, C.; Moncorgé, R.; Sun, Y.; Cone, R. L.; Zannoni, E.; Cavalli, E.; Bettinelli, M.

2000-02-01

139

Stress- Corrosion cracking of copper single crystals  

NASA Astrophysics Data System (ADS)

Constant extension rate tests have been carried out on copper single crystals in a sodium nitrite solution, using an applied potential to accelerate the cracking. Crack velocities up to 30 nm per second were obtained at 30 °C. The stress-corrosion fracture surfaces are cleavage-like, with curved striations parallel to the crack front. If the dynamic straining is stopped, the cracks apparently stop growing within about 20 /?m. The steps between adjacent flat facets are more energy-absorbing than in a-brass, providing a possible explanation for the importance of dynamic strain. Simultaneous acoustic emission and electrochemical current transients have been measured, and suggest that cracking proceeds by discontinuous cleavage.

Sieradzki, K.; Sabatini, R. L.; Newman, R. C.

1984-10-01

140

Structural analysis of vertically-aligned single crystalline ZnO nanorods grown on different seed layers with chemical solution deposition.  

PubMed

We report the structural properties of the vertically-oriented ZnO nanorods fabricated on various ZnO seed layers with chemical solution deposition (CSD) technique. The ZnO nanorods were prepared using an aqueous solution with Zinc nitrate (Zn(NO3)2 x 6H2O, Aldrich) and hexamethylenetetramine (HMT, Aldrich) in a convection oven. A-plane sapphire substrates with a deposited ZnO thin film were placed upside down in a quartz holder to avoid any micro-crystalline contamination. Especially, our hydro-thermal syntheses are automatically processed on precision pump drive systems (Masterflex) to accurately control the pH of the aqueous solution. The [002] crystal orientation of the ZnO seed layer was observed by the X-ray diffraction pattern. Structural features of ZnO nanorods were systematically analyzed by scanning electron microscopy and tunneling electron microscopy, together with selective area electron diffraction patterns. Experimental observations clearly demonstrated the dependence of the growth direction of the ZnO nanorods on the crystal structures of the ZnO seed layers. PMID:22966704

Ko, Wonbae; Lee, Sang Hyo; Lee, Jun Seok; Hong, Jin Pyo

2012-07-01

141

TOPICAL REVIEW: Organic field-effect transistors using single crystals  

Microsoft Academic Search

Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of

Tatsuo Hasegawa; Jun Takeya

2009-01-01

142

Magnetoresistance of 3d transition metal single-doped and co-doped epitaxial ZnO thin films  

NASA Astrophysics Data System (ADS)

Magnetoresistance (MR) of transition metal (TM)-doped and co-doped ZnO films prepared by a magnetron sputtering system has been discussed. For single-doped film, the values of Hmax (the field at which MR shows its maximum) increase as temperature increases. At a certain temperature, the values of Hmax increase from Mn-, Fe- to Co-doped films due to their different magnetic moments. For (Mn, Fe), (Mn, Co)-co-doped ZnO films, the MR behaviors show striking similarity as Mn-doped ZnO film. These results are interpreted in terms of the s-d spin-splitting mechanism. Large negative MR in high field is attributed to the formation of magnetic polarons (MPs). The temperature dependence of resistivity agrees well with the variable range hopping (VRH) mechanism of MPs.

Ji, Gen-Hua; Gu, Zheng-Bin; Lu, Ming-Hui; Wu, Di; Zhang, Shan-Tao; Zhu, Yong-Yuan; Zhu, Shi-Ning; Chen, Yan-Feng; Pan, X. Q.

2009-05-01

143

Three-dimensional single crystal silicon micromachining  

NASA Astrophysics Data System (ADS)

A monolithic, multiple-level (ML), single-crystal-silicon (SCS) micromachining process called SCREAM3D has been developed. The high-aspect-ratio (HAR) levels are self-aligned and are fabricated from a single substrate by deep etching. Anisotropic reactive ion etching of silicon has been studied in detail and new recipes for the vertical etch and release of HAR ML structures have been developed. The SCREAM3D levels are electrically isolated from the substrate and one another using a novel ML isolation scheme, which requires only a single lithography and metallization step, regardless of the number of levels. Two- and three-level SCREAM3D devices have been fabricated. They demonstrate three device concepts: ML microelectromechanical systems (MEMS), micromachined electron gun arrays (MEGA) and ML actuators for out-of-plane deflection. ML MEMS consist of several suspended levels moving relative to each other. They can be coupled mechanically and/or electrically. One example is a novel clamp-alignment device which uses the relative translation of two initially self-aligned apertures to grip and align an external component (such as an optical fiber) to the wafer. MEGA is a multiple-beam architecture to increase the throughput of electron beam lithography. MEGA is an array of identical electron sources, consisting of silicon field emitters with integrated electrostatic lenses. The parallel operation of a large number (N = 10,000) of sources is required to increase the total current and throughput (60 8"-wafers/hour) of the system while maintaining standard single-beam parameters (10nA, 20MHz exposure rate) and limiting charge-interaction effects. ML actuators have been studied by numerical simulation. All four designs outperform comparable single-level actuators: the generated force is up to five times larger, and the range of motion up to ten times greater. Two of the ML designs operate bi-directionally and one design can be used to form a bi-stable system. Several of the actuators have been integrated with torsional and z-motion-stages and experimentally characterized using laser vibrometry. SCREAM3D extends SCS bulk-micromachining to multiple-level structures. The self-aligned, high-aspect-ratio levels allow the implementation of more efficient device designs and novel ML device concepts. Complex actuators, generating larger forces in reduced chip area, can be fabricated and entire microinstruments can be integrated on a single wafer.

Hofmann, Wolfgang Maximilian Josef

1999-11-01

144

P-185 / L. Tan P-185: Single Cell Gap Single Mode Transflective Liquid Crystal Display  

E-print Network

P-185 / L. Tan P-185: Single Cell Gap Single Mode Transflective Liquid Crystal Display with High Kong Abstract A transflective liquid crystal display with single cell gap single mode structure of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong

145

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-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.

Todt, Volker (Lemont, IL); Miller, Dean J. (Darien, IL); Shi, Donglu (Oak Park, OH); Sengupta, Suvankar (Columbus, OH)

1998-01-01

146

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

147

Characterization and growth of magnesium diboride single crystals  

Microsoft Academic Search

Single crystals of magnesium diboride with maximum dimension of 200×200×60?m3 have been successfully grown from copper flux in iron capsules. MgB2 crystallized separately in a system with the composition Mg40Cu40B20, and large single crystals were grown. Crystals grow together in the system with the composition Mg35Cu40B25, and MgB4 is found in this system due to excess B content. MgB2 crystallizes

Z. X. Cheng; X. L. Wang; A. V. Pan; H. L. Liu; S. X. Dou

2004-01-01

148

Fractoemission from cyclotrimethylenetrinitramine (RDX) explosive single crystals  

NASA Astrophysics Data System (ADS)

Production-grade Class D and laboratory-grown cyclotrimethylenetrinitramine (RDX) explosive crystals were fractured in a vacuum (10-5 Pa) while viewed by particle detectors biased to separate positive and negative charge. Fracture was achieved by compressive loading (both production and laboratory crystals) and by three-point bending (laboratory crystals only). ``Cleavage''-type fracture resulted for several crystals subjected to three-point bending and yielded a sharp emission peak followed by rapid decay. Longer and more intense emission was observed for a few crystals broken in flexure which may correspond to more ``energetic'' fracture. Multiple fracture, involving surface frictional grinding, occurred for crystals that were compressed; in this case, relatively intense emission resulted which continued for several minutes after fracturing the crystals. These results are discussed in terms of possible mechanisms.

Dickinson, J. T.; Miles, M. H.; Elban, W. L.; Rosemeier, R. G.

1984-06-01

149

Ultraviolet electroluminescence from hetero p-n junction between a single ZnO microsphere and p-GaN thin film.  

PubMed

We report ultraviolet electroluminescence from a hetero p-n junction between a single ZnO microsphere and p-GaN thin film. ZnO microspheres, which have high crystalline quality, have been synthesized by ablating a ZnO sintered target. It was found that synthesized ZnO microspheres had a high-optical property and exhibit the laser action in the whispering gallery mode under pulsed optical pumping. A hetero p-n junction was formed between the single ZnO microsphere/ p-GaN thin film, and a good rectifying property with a turn-on voltage of approximately 6 V was observed in I-V characteristic across the junction. Ultraviolet and visible electroluminescence were observed under forward bias. PMID:24787884

Tetsuyama, Norihiro; Fusazaki, Koshi; Mizokami, Yasuaki; Shimogaki, Tetsuya; Higashihata, Mitsuhiro; Nakamura, Daisuke; Okada, Tatsuo

2014-04-21

150

Chemical Solution Routes to Single-Crystal Thin Films  

Microsoft Academic Search

Epitaxial thin films of inorganic single crystals can be grown on single-crystal substrates with a variety of different solution chemistries. This review emphasizes chemical solution deposition, in which a solution is used to deposit a layer of precursor molecules that decompose to low-density, polycrystalline films during heating. Ways to control film cracking during deposition and heat treatment and why many

F. F. Lange

1996-01-01

151

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

152

A Quick Method for Determining the Density of Single Crystals.  

ERIC Educational Resources Information Center

Shows how the Archimedes method is used to determine the density of a single crystal of ammonium oxalate monohydrate. Also shows how to calculate the density of other chemicals when they are available as single crystals. Experimental procedures and materials needed are included. (JN)

Roman, Pascual; Gutierrez-Zorrilla, Juan M.

1985-01-01

153

A Multivariant model for single crystal shape memory alloy behavior  

Microsoft Academic Search

A general 3-D multivariant model based on thermodynamics and micromechanics for single crystal shape memory alloy (SMA) behavior is presented. This model is based on the habit plane and transformation directions for the variants of martensite in a given material. From this information, the single crystal behavior of the material to temperature and mechanical loads is derived using the concept

Miinshiou Huang; L. C. Brinson

1998-01-01

154

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

155

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

156

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

NASA Astrophysics Data System (ADS)

We report mass-resolved time-of-flight measurements of neutral particles from the (101¯0) 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.

Khan, Enamul H.; Langford, S. C.; Dickinson, J. T.; Boatner, L. A.

2013-08-01

157

Cleavage oriented iron single crystal fracture toughness  

NASA Astrophysics Data System (ADS)

Fundamental understanding of atomic level mechanisms controlling cleavage fracture in bcc metals, and the corresponding brittle to ductile transition (BDT) has been a long sought, 'grand challenge' of science. This is particularly true for the BDT in Fe, which is among vital elements that underpin our technological civilization. A key obstacle to developing an understanding of the BDT in Fe is the absence of a reliable database on the temperature dependence of toughness in Fe. In ferritic alloys, the micro-arrest toughness of ferrite, Kmu(T), is hypothesized to control macroscopic cleavage. As a surrogate for Kmu(T), special techniques were developed to measure the arrest toughness, Ka(T), for cleavage oriented, Fe single crystals. Further, the mechanisms controlling cleavage and the BDT should be reflected in the loading rate dependence of static-dynamic initiation toughness, K Ic and KId. Thus KIc/d(T) were also measured for K-rate from 10-1 to 104 MPa?m/s. These studies led to the following conclusions: (1) Ka is semi-brittle, increasing from an average of ? 3.5 MPa?m at -196°C to ? 9 MPa?m at 0°C. (2) The (100) Ka are similar in the [010] and [011] and orientations, but cleavage does not occur on (110) planes. (3) The Ka for unalloyed Fe is about 150°C lower than that for Fe-3wt%Si, suggesting that equivalent Ka may occur at equivalent lattice sigmay. (4) Higher K-rate shift K Ic/d(T) curves to higher T. (5) The shifts of the KIc/d(T) and Ka(T) curves can be understood and modeled based on dislocation dynamics concepts for the glide of screw dislocations with a stress (and T) controlled activation energy, Ea, with a maximum value of about ? 0.5 eV. (6) This Ea is consistent with a double kink nucleation mechanism. Etch pit, slip trace and ledge patterns on side, fracture and sectioned surfaces of the crystals were characterized to study dislocation activity associated with cleavage and the BDT. The results showed extensive dislocation activity on {110}<111> and {211}<111> slip systems. Consistent with its semi-brittle nature, there is evidence of significant dislocation glide and multiplication during cleavage, perhaps associated with pre-existing dislocations.

Hribernik, Michael Louis

158

Growing vertical ZnO nanorod arrays within graphite: efficient isolation of large size and high quality single-layer graphene.  

PubMed

We report a unique strategy for efficiently exfoliating large size and high quality single-layer graphene directly from graphite into DMF dispersions by growing ZnO nanorod arrays between the graphene layers in graphite. PMID:23736256

Ding, Ling; E, Yifeng; Fan, Louzhen; Yang, Shihe

2013-07-18

159

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

160

Ferroelectric polarization reversal in single crystals  

NASA Technical Reports Server (NTRS)

Research on the reversal of polarization in ferroelectric crystals is reviewed. Particular attention is given to observation methods for polarization reversal, BaTiO3 polarization reversal, crystal thickness dependence of polarization reversal, and domain wall movement during polarization reversal in TGS.

Stadler, Henry L.

1992-01-01

161

Method for harvesting rare earth barium copper oxide single crystals  

DOEpatents

A method of preparing high temperature superconductor single crystals. 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.

Todt, Volker R. (Lemont, IL); Sengupta, Suvankar (Columbus, OH); Shi, Donglu (Cincinnati, OH)

1996-01-01

162

Method for harvesting single crystals from a peritectic melt  

DOEpatents

A method of preparing 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, cooling the peritectic mixture to quench directly the mixture on a porous, wettable inert substrate to wick off the peritectic liquid, leaving single crystals 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 unmelted, allowing the wicking away of the peritectic liquid. 2 figs.

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

1996-08-27

163

Method for harvesting single crystals from a peritectic melt  

DOEpatents

A method of preparing single crystals. 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, cooling the peritectic mixture to quench directly the mixture on a porous, wettable inert substrate to wick off the peritectic liquid, leaving single crystals 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 unmelted, allowing the wicking away of the peritectic liquid.

Todt, Volker R. (Lemont, IL); Sengupta, Suvankar (Columbus, OH); Shi, Donglu (Cincinnati, OH)

1996-01-01

164

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

165

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  

NASA Astrophysics Data System (ADS)

In past studies, we have observed copious emissions of ionic and atomic Zn from single-crystal ZnO accompanying irradiation of single-crystal ZnO with 193-nm excimer laser irradiation at fluences below the onset of optical breakdown. The Zn+ and ground state Zn° are studied using time-of-flight techniques and are mass selected using a quadrupole mass spectrometer. Simultaneously, we have observed emitted particles that are detectable with a Channeltron electron multiplier but cannot be mass selected. It is a reasonable hypothesis that these particles correspond to a neutral atom or molecule in highly excited long lived states. We provide strong evidence that they correspond to high lying Rydberg states of atomic Zn. We propose a production mechanism involving laser excitation via a two photon resonance excitation of Zn°.

Khan, Enamul H.; Langford, S. C.; Dickinson, J. T.; Boatner, L. A.

2014-08-01

166

A Single Crystal Niobium RF Cavity of the TESLA Shape  

SciTech Connect

A fabrication method for single crystal niobium cavities of the TESLA shape was proposed on the basis of metallographic investigations and electron beam welding tests on niobium single crystals. These tests showed that a cavity can be produced without grain boundaries even in the welding area. An appropriate annealing allows the outgassing of hydrogen and stress relaxation of the material without destruction of the single crystal. A prototype single crystal single cell cavity was build. An accelerating gradient of 37.5 MV/m was reached after approximately 110 {mu}m of Buffered Chemical Polishing (BCP) and in situ baking at 120 deg. C for 6 hrs with a quality factor exceeding 2x1010 at 1.8 K. The developed fabrication method can be extended to fabrication of multi cell cavities.

Singer, W.; Singer, X.; Kneisel, P. [DESY, Notkestrasse 85, D-22607 Hamburg (Germany); Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States)

2007-08-09

167

A Single Crystal Niobium RF Cavity of the TESLA Shape  

SciTech Connect

A fabrication method for single crystal niobium cavities of the TESLA shape was proposed on the basis of metallographic investigations and electron beam welding tests on niobium single crystals. These tests showed that a cavity can be produced without grain boundaries even in the welding area. An appropriate annealing allows the outgassing of hydrogen and stress relaxation of the material without destruction of the single crystal. A prototype single crystal single cell cavity was built. An accelerating gradient of 37.5 MV/m was reached after approximately 110 mu-m of Buffered Chanical Polishing (BCP) and in situ baking at 120°C for 6 hrs with a quality factor exceeding 2x1010 at 1.8 K. The developed fabrication method can be extended to fabrication of multi cell cavities.

W. Singer; X. Singer; P. Kneisel

2007-09-01

168

Paramagnetism in Mn\\/Fe implanted ZnO  

Microsoft Academic Search

Prompted by the generally poor understanding of the nature of magnetic phenomena in 3d-metal doped ZnO, we have undertaken on-line 57Fe Mössbauer spectroscopy on ZnO single crystals in an external magnetic field of 0.6 T, following the implantation of radioactive 57Mn ions at room temperature. The Mössbauer spectra of the dilute Fe impurities are dominated by sextets whose angular dependence

H. P. Gunnlaugsson; T. E. Mølholt; R. Mantovan; H. Masenda; D. Naidoo; W. B. Dlamini; R. Sielemann; K. Bharuth-Ram; G. Weyer; K. Johnston; G. Langouche; S. Ólafsson; H. P. Gíslason; Y. Kobayashi; Y. Yoshida; M. Fanciulli

2010-01-01

169

Dielectric and baric characteristics of TlS single crystal  

NASA Astrophysics Data System (ADS)

The investigation of the frequency dependences of the dielectric coefficients and ac-conductivity of the TlS single crystals made it possible to elucidate the nature of dielectric loss and the charge transfer mechanism. Moreover, we evaluated the density and energy spread of localized states near the Fermi level, the average hopping time and the average hopping length. It was shown that the dc-conductivity of the TlS single crystals can be controlled by varying the hydrostatic pressure. This has opened up possibilities for using TlS single crystals as active elements of pressure detectors.

Mustafaeva, S. N.; Asadov, M. M.; Ismailov, A. A.

2014-11-01

170

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

171

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

172

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

173

X-Ray Study of Polygonization in Copper Single Crystals  

Microsoft Academic Search

Single crystals of electrolytic tough pitch copper and of high purity (99.999%) copper were deformed by bending. The substructure in the as-bent and annealed crystals was studied by means of sensitive x-ray techniques. It was found that regardless of purity, crystals of certain orientations in the as-bent condition do not have sub-boundaries detectable by the methods used. Polygonization took place

C. T. Wei; M. N. Parthasarathi; P. A. Beck

1957-01-01

174

Off-axis sputter deposition of ZnO films on c-sapphire substrates with buffer layers prepared via nitrogen-mediated crystallization  

NASA Astrophysics Data System (ADS)

High-quality epitaxial ZnO films on c-plane sapphire substrates have been obtained by utilizing off-axis sputtering configuration together with buffer layers prepared via nitrogen mediated crystallization (NMC). The role of NMC buffer layers is to provide high density of nucleation site and thus to reduce the strain energy caused by the large lattice mismatch (18%) between ZnO and sapphire. The NMC buffer layers allow two dimensional (2D) growth of subsequently grown ZnO films, being particularly enhanced by employing off-axis sputtering configuration, in which the substrate is positioned out of the high-energy particles such as negative oxygen ions originating from the targets. As a result, ZnO films with smooth surfaces (root-mean-square roughness: 0.76 nm) and high electron mobility of 88 cm2/V?sec are fabricated. Photoluminescence spectra of the ZnO films show strong near-band-edge emission, and the intensity of the orange-red defect emission significantly decreases with increasing the horizontal distance between the target and the substrate. From these results, we conclude that off-axis sputtering together with NMC buffer layers is a promising method for obtaining high quality epitaxial ZnO films.

Itagaki, N.; Matsushima, K.; Yamashita, D.; Seo, H.; Koga, K.; Shiratani, M.

2014-03-01

175

Mesoporous silicon photonic crystal microparticles: towards single-cell optical  

E-print Network

Mesoporous silicon photonic crystal microparticles: towards single-cell optical biosensors Bin Guan such as the coupling of antibodies. The surface chemistry remained unchanged after sonication of the PSi to form PSi crystals, with complicated multilayer structures, to be produced. High- quality optical structures

Kilian, Kristopher A.

176

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

177

Electrochemistry of transition metal single crystals with well defined surfaces  

Microsoft Academic Search

The effect of extended defects of the surface of metallic single crystals on the electrochemical processes of dissolution and formation of a new phase has been analysed. Theoretical ideas on the rearrangement of a crystal surface (phase transitions of the second kind) during the adsorption of surface-active substances are presented. The reconstruction (faceting) of the surface under the influence of

Gennadii V. Khaldeev; T. A. Syur

1992-01-01

178

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

179

The Herbertsmithite Hamiltonian: ?SR measurements on single crystals  

E-print Network

We present transverse field muon spin rotation/relaxation measurements on single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find that the spins are more easily polarized when the field is perpendicular ...

Ofer, Oren

180

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

181

Synthesis and physical characterization of thermoelectric single crystals  

E-print Network

There is much current interest in thermoelectric devices for sustainable energy. This thesis describes a research project on the synthesis and physical characterization of thermoelectric single crystals. 1In?Se?-[delta] ...

Porras Pérez Guerrero, Juan Pablo

2012-01-01

182

Aluminium segregation of TiAl during single crystal growth  

SciTech Connect

{gamma}-TiAl single crystals have been successfully prepared by an induction-heated cold crucible Czochralski technique which offers more flexibility than vertical float zoning. Compositional analysis of the Czochralski grown single crystals indicates a homogeneous composition after initial transition; and the average composition is close to the peritectic composition. However, {gamma}-TiAl single crystals prepared by vertical float zoning show a small aluminium segregation profile along the growth direction; and the average composition of the as-grown crystals is close to that of the starting alloy. Compositional analysis further demonstrated the banded structure with alternative single {gamma}-phase and {alpha}{sub 2} + {gamma} lamellar regions in the vertical float zoned Ti-54 at.% Al.

Bi, Y.J.; Abell, J.S. [Univ. of Birmingham (United Kingdom). School of Metallurgy and Materials] [Univ. of Birmingham (United Kingdom). School of Metallurgy and Materials

1997-09-15

183

High polarization single dipole mode photonic crystal microlaser  

Microsoft Academic Search

A photonic crystal microlaser with elongate lattice was fabricated. Lasing action of single mode, y-dipole mode, was observed. With this mode, a high polarization extinction ratio of 51:1 was obtained.

Wei Chen; Mingxin Xing; Wenjun Zhou; Anjin Liu; Lianghui Chen; Wanhua Zheng

2009-01-01

184

Superconducting Proximity Effect in Single-Crystal Nanowires  

E-print Network

This dissertation describes experimental studies of the superconducting proximity effect in single-crystal Pb, Sn, and Zn nanowires of lengths up to 60 um, with both ends of the nanowires in contact with macroscopic electrodes that are either...

Liu, Haidong

2010-07-14

185

Piezoelectric properties of tetragonal single-domain Mn-doped NBT-6 %BT single crystals  

NASA Astrophysics Data System (ADS)

We report a study of properties of Mn-doped NBT-6 %BT single crystals. We show that tetragonal single-domain states can be stabilized by poling along a [001] direction. For carefully prepared crystals, the piezoelectric coefficient can reach 570 pC/N. When poled along non-polar directions, the crystals exhibit ferroelectric domain structures consistent with tetragonal micron-sized domains, as revealed by optical observation and Raman spectroscopy. The multidomain crystals have lower values, 225 and 130 pC/N for [011] and [111]-oriented crystals, respectively. This trend is commented on from a domain-engineering perspective.

Guennou, Mael; Savinov, Maxim; Drahokoupil, Jan; Luo, Haosu; Hlinka, Jirka

2014-07-01

186

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

187

Green emission in carbon doped ZnO films  

NASA Astrophysics Data System (ADS)

The emission behavior of C-doped ZnO films, which were prepared by implantation of carbon into ZnO films, is investigated. Orange/red emission is observed for the films with the thickness of 60-100 nm. However, the film with thickness of 200 nm shows strong green emission. Further investigations by annealing bulk ZnO single crystals under different environments, i.e. Ar, Zn or C vapor, indicated that the complex defects based on Zn interstitials are responsible for the strong green emission. The existence of complex defects was confirmed by electron spin resonance (ESR) and low temperature photoluminescence (PL) measurement.

Tseng, L. T.; Yi, J. B.; Zhang, X. Y.; Xing, G. Z.; Fan, H. M.; Herng, T. S.; Luo, X.; Ionescu, M.; Ding, J.; Li, S.

2014-06-01

188

Single step deposition of different morphology ZnO gas sensing films  

Microsoft Academic Search

Al-doped ZnO thin films were deposited onto fixed silicon substrates by dc reactive sputtering. The inherent lateral inhomogeneity in the deposited film with areas of different morphology and sheet resistance revealed different sensing properties. This novel approach offers the possibility of controllable deposition of ZnO sensing layers for the simultaneous manufacturing of sensors with different properties in an array in

Á. Németh; E. Horváth; Z. Lábadi; L. Fedák; I. Bársony

2007-01-01

189

Laser-induced hydrophobicity on single crystal zinc oxide surface  

NASA Astrophysics Data System (ADS)

Highly hydrophobic surface of ZnO crystal substrate is prepared easily and rapidly by KrF excimer laser irradiation. The water contact angle is increased from 70° to approximately 120°. Through the XRD, AFM, XPS measurements and the Cassie-Baxter model analysis, it is indicated that the unique micro-nano fluctuant surface structure induced by laser irradiation is the prominent factor to the great increase of the water CA. The annealing treatments for the irradiated sample are carried out both in oxygen and vacuum atmosphere. It is found that the adsorption of oxygen atoms on the roughened surface could make the CA decrease abruptly at the first beginning, and after being stored at ambient atmosphere, the CA would reconvert to the value of the freshly irradiated sample gradually. It probably provides a convenient method for rapid conversion of the wettability through excimer laser irradiation and post annealing treatment.

Xie, Sijing; Zhao, Yan; Jiang, Yijian

2012-12-01

190

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

191

Constitutive modeling of creep of single crystal superalloys  

E-print Network

of single crystal nickel based superalloys developed over last few decades. The second and third generation of superalloys are characterized by increasing concentration of Rhenium which improves creep and fatigue resistance. Fourth gener- ation superalloys... of single crystal nickel based superalloys developed over last few decades. The second and third generation of superalloys are characterized by increasing concentration of Rhenium which improves creep and fatigue resistance. Fourth gener- ation superalloys...

Prasad, Sharat Chand

2006-10-30

192

250 W single-crystal fiber Yb:YAG laser.  

PubMed

We demonstrate an Yb:YAG single-crystal fiber laser with 251 W output power in continuous-wave and an optical efficiency of 44%. This performance can be explained by the high overlap between pump and signal beams brought by the pump guiding and by the good thermal management provided by the single-crystal fiber geometry. The oscillator performance with a reflectivity of the output coupler as low as 20% also shows high potential for power amplification. PMID:22825171

Délen, Xavier; Piehler, Stefan; Didierjean, Julien; Aubry, Nicolas; Voss, Andreas; Ahmed, Marwan Abdou; Graf, Thomas; Balembois, Francois; Georges, Patrick

2012-07-15

193

Thermal and dielectric studies of nickel malonate dihydrate single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of nickel malonate dihydrate were grown by the gel technique, employing the single diffusion method. Thermal dehydration of the crystal was investigated by thermogravimetric and differential thermal analyses. The title compound exhibits a steady thermal behaviour at higher temperature range of 350-800 °C. The dielectric properties of the prepared sample were analyzed as a function of frequency in the range of 1 kHz-1 MHz and at temperatures between 40 and 140 °C.

Mathew, Varghese; Mathai, K. C.; Mahadeven, C. K.; Abraham, K. E.

2011-02-01

194

Forward diffracted parametric X radiation from a silicon single crystal  

NASA Astrophysics Data System (ADS)

Experiments were performed with the 855 MeV electron beam of the Mainz Microtron MAMI which focused on still open questions in the X-ray emission process upon traversal of ultra relativistic electrons through single crystals. To elucidate the quest of kinematical versus dynamical production of PXR the radiation from silicon single crystal targets, emitted close to the electron direction, has been studied. The observed interference structures show that PXR is produced in a dynamical process.

Backe, H.; Rueda, A.; Lauth, W.; Clawiter, N.; El-Ghazaly, M.; Kunz, P.; Weber, T.

2005-05-01

195

Annealing Effect on Photovoltages of Quartz Single Crystals  

Microsoft Academic Search

We investigate the photovoltaic effects of quartz single crystals annealed at high temperatures in ambient atmosphere. The open-circuit photovoltages and surface morphologies strongly depend on the heating treatments. When the annealing temperature increases from room temperature to 900°C, the rms roughness of quartz single crystal wafers increases from 0.207 to 1.011 nm. In addition, the photovoltages decrease from 1.994muV at

Lu Tian; Song-Qing Zhao; Kun Zhao

2010-01-01

196

Synthesis and Single-Crystal Growth of Ca  

SciTech Connect

For the study of the quasi-two-dimensional Mott transition system Ca{sub 2-x}Sr{sub x}RuO{sub 4}, we have succeeded in synthesizing polycrystalline samples and also growing single crystals by a floating-zone method. Details of the preparations for the entire solution range are described. The structural, transport, and magnetic properties of both polycrystalline and single-crystal samples are fully in agreement.

Nakatsuji, Satoru; Maeno, Yoshiteru

2001-01-01

197

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

SciTech Connect

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., E-mail: slgupta@iitk.ac.in; Thareja, Raj K. [Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, U.P. (India)

2013-12-14

198

Single femtosecond laser pulse-single crystal formation of glycine at the solution surface  

NASA Astrophysics Data System (ADS)

We demonstrate femtosecond laser-induced crystallization of glycine from its supersaturated solution depending on laser tunable parameters (pulse energy and repetition rate) and focal position, and examine the crystallization probability, crystal morphology, and crystal polymorph. The generation of cavitation bubble through multiphoton absorption of water depends on input laser pulse energy and repetition rate, which strongly determine morphology and number of the obtained crystals. Significant increase in the crystallization probability is observed by irradiating the femtosecond laser pulses to the air/solution interface, and single pulse-induced single crystal formation is successfully achieved. The crystallization mechanism is discussed in view of inhomogeneous mechanical stress induced by cavitation bubble generation and molecular assembly characteristics of the surface.

Liu, Tsung-Han; Uwada, Takayuki; Sugiyama, Teruki; Usman, Anwar; Hosokawa, Yoichiroh; Masuhara, Hiroshi; Chiang, Ting-Wei; Chen, Chun-Jung

2013-03-01

199

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

200

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.

2014-10-01

201

Growth, Crystal Structure, and Thermopower of Single Crystals of UNi 1.9Sn  

Microsoft Academic Search

We have grown single crystals of UNi1.9(1)Sn from a semi-levitated melt using the Kyropoulos technique. The crystal structure of UNi1.9(1)Sn was determined by single-crystal X-ray diffraction and refined to a residual value of R=0.0336. This compound crystallizes in the cubic MnCu2Al-type structure with the lattice parameter a=6.4633(4) Å. The temperature dependence of the thermoelectric power, different from that observed for

L. Shlyk; J. C. Waerenborgh; M. Almeida

2000-01-01

202

Solution Growth of Rubrene Single Crystals Using Various Organic Solvents  

NASA Astrophysics Data System (ADS)

To fabricate organic field-effect transistors (OFETs) with high carrier mobility, we attempted to grow 5,6,11,12-tetraphenylnaphthacene (rubrene) single crystals from solution and to improve their quality. Investigations into solvents in which rubrene was highly soluble proved that its solubility depended on the presence or absence of aromatic rings and chloro groups rather than on the polarity of the solvents. Rubrene crystals were grown from aromatic solvents, specifically from toluene, p-xylene, and aniline solvents, as well as from 1,2-dichloroethane (DCE) solvent. As a result, rubrene single crystals larger than 1 mm were obtained. Powder X-ray diffraction (XRD) analysis showed that the crystals obtained from the p-xylene and toluene solvents were rubrene, and 1H-nuclear magnetic resonance (1H-NMR) measurement proved that the crystals had not incorporated the solvent at the detection level. In addition, atomic force microscopy (AFM) confirmed that the rubrene crystals grown from the p-xylene and aniline solvents had flat faces and that the crystal from the p-xylene solvent had monomolecular steps on parts of the surfaces. Rubrene single crystal OFETs with graphite electrodes and parylene as an insulator showed carrier mobilities of ?0.75 cm2 V-1 s-1.

Matsukawa, Takeshi; Takahashi, Yoshinori; Tokiyama, Tsukasa; Sasai, Kenichi; Murai, Yusuke; Hirota, Nobuhiro; Tominari, Yukihiro; Mino, Norihisa; Yoshimura, Masashi; Abe, Masayuki; Takeya, Junichi; Kitaoka, Yasuo; Mori, Yusuke; Morita, Seizo; Sasaki, Takatomo

2008-12-01

203

Growth and properties of benzil doped benzimidazole (BMZ) single crystals  

SciTech Connect

In the present work, we have made an attempt to study the effect of benzil doping on the properties of benzimidazole single crystals. For this purpose we have grown pure and benzil doped benzimidazole single crystals by vertical Bridgman technique. The grown crystals were characterized by various characterization techniques. The presence of dopants confirmed by powder X-ray diffraction (XRD). Crystalline perfection of the grown crystals has been analysed by high-resolution X-ray diffraction (HRXRD). The transmittance, electrical property and mechanical strength have been analysed using UV-vis-NIR spectroscopic, dielectric and Vicker's hardness studies. The relative second harmonic generation efficiency of pure and doped benzimidazole crystals measured using Kurtz powder test.

Babu, R. Ramesh, E-mail: rampap2k@yahoo.co.in [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India); Sukumar, M. [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India)] [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Vasudevan, V. [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India) [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India); Shakir, Mohd. [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)] [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India); Ramamurthi, K. [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India)] [Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024 (India); Bhagavannarayana, G. [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)] [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)

2010-09-15

204

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

205

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Structural and Electrical Properties of Single Crystalline Ga-Doped ZnO Thin Films Grown by Molecular Beam Epitaxy  

Microsoft Academic Search

High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a-plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about

Zhong-Lin Lu; Wen-Qin Zou; Ming-Xiang Xu; Feng-Ming Zhang; You-Wei Du

2009-01-01

206

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

207

Photorefractive Properties of Stoichiometric Lithium Niobate Single Crystals  

SciTech Connect

The specific features of photorefractive light scattering in nominally pure stoichiometric (Li/Nb = 1) sin- gle crystals grown from a melt with 58.6 mol % Li{sub 2}O (LiNbO{sub 3}st) and in the stoichiometric single crystals grown from a melt of congruent composition in the presence of K{sub 2}O flux (LiNbO{sub 3}stK{sub 2}O) have been investi- gated. At an excitation power of 30 mW, LiNbO{sub 3}stK{sub 2}O single crystals are found to exhibit a stronger photo- refractive effect than LiNbO{sub 3}st single crystals.

Sidorov, N. V. [Russian Academy of Sciences, Institute of Chemistry and Technology of Rare Earth Elements and Mineral Raw Materials, Kola Scientific Center (Russian Federation); Antonycheva, E. A.; Syui, A. V. [Far Eastern State Transport University (Russian Federation); Palatnikov, M. N., E-mail: palat_mn@chemy.kolasc.net.ru [Russian Academy of Sciences, Institute of Chemistry and Technology of Rare Earth Elements and Mineral Raw Materials, Kola Scientific Center (Russian Federation)

2010-11-15

208

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

209

VGF growth of germanium single crystals without crucible contact  

NASA Astrophysics Data System (ADS)

Experimental results on the vertical gradient freeze growth of germanium single crystals without crucible contact are presented. Two different approaches to establish a stable pressure difference necessary for avoiding the contact between crystal and crucible on solidification are described. Germanium crystals with a diameter of up to 3 in were grown almost without contact to the crucible wall. The effect of detachment is discussed with respect to the microscopical surface roughness and dislocation density of the grown crystals. In comparison to conventionally grown reference crystals the structural perfection of the detached-grown crystals is found to be much higher which can be attributed to the reduced thermal and thermo-mechanical stress in growth without wall contact.

Langheinrich, D.; Pätzold, O.; Raabe, L.; Stelter, M.

2010-08-01

210

Stress-induced single-polarization single-transverse mode photonic crystal fiber with low nonlinearity  

Microsoft Academic Search

We report on the design of a single-polarization single-transverse mode large mode area photonic crystal fiber. By including index-matched stress applying elements in the photonic cladding an ultra-broadband single polarization window is obtained while a large mode field area of ~700 mum is maintained. Based on that design, an Yb-doped double-clad photonic crystal fiber is realized that combines low nonlinearity

T. Schreiber; F. Röser; O. Schmidt; J. Limpert; R. Iliew; F. Lederer; A. Petersson; C. Jacobsen; K. P. Hansen; J. Broeng; A. Tünnermann

2005-01-01

211

Direct growth of single-walled carbon nanotubes on conducting ZnO films and its field emission properties  

SciTech Connect

Despite the necessity of direct growth of single-walled carbon nanotubes (SWNTs) on conducting films for versatility of designing device architectures for nanoelectronics and optoelectronics, most of SWNT growths have been carried out on insulating films or supporting materials such as SiO{sub 2} and Al{sub 2}O{sub 3}. Here, the authors report that conducting ZnO films can be used as both an underlying layer for the SWNT growth and an electrode for device operation. ZnO films with a resistivity in the order of 10{sup -3} {omega} cm were deposited by atomic layer deposition. SWNTs were directly grown on the ZnO film by water plasma chemical vapor deposition. The authors demonstrate field emission properties from the SWNT/ZnO cathode, of which the turn-on electric field for a current density of 10 {mu}A/cm{sup 2} and the field enhancement factor are 1.8 V/{mu}m and 3200, respectively.

Min, Yo-Sep; Bae, Eun Ju; Kim, Un Jeong; Park, Wanjun; Hwang, Cheol Seong [Materials and Devices Research Center, Samsung Advanced Institute of Technology, Yongin 449-712 (Korea, Republic of); School of Materials Science and Engineering, Seoul National University, Seoul 151-742 (Korea, Republic of)

2006-09-11

212

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

213

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

214

''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

215

Inspection of Single Crystal Aerospace Components with Ultrasonic Arrays  

NASA Astrophysics Data System (ADS)

Single crystal metal alloys are used extensively in the manufacture of jet engine components for their excellent mechanical properties at elevated temperatures. The increasing use of these materials and demand for longer operational life and improved reliability motivates the requirement to have capable NDE methods available. Ultrasonic arrays are well established at detecting sub-surface defects however these methods are not currently suitable to the inspection of single crystal components due to their high elastic anisotropy causing directional variation in ultrasonic waves. In this paper a model of wave propagation in anisotropic material is used to correct an ultrasonic imaging algorithm and is applied to single crystal test specimens. The orientation of the crystal in a specimen must be known for this corrected-algorithm therefore a crystal orientation method is also presented that utilizes surface skimming longitudinal waves under a 2D array. The work detailed in this paper allows an ultrasonic 2D array to measure the orientation of a single crystal material and then perform accurate volumetric imaging to detect and size defects.

Lane, C. J. L.; Dunhill, A.; Drinkwater, B. W.; Wilcox, P. D.

2010-02-01

216

Effect of solution concentration on the functional properties of ZnO nanostructures: Role of Hexamethylenetetramine  

NASA Astrophysics Data System (ADS)

In this research, ZnO nanorods have been successfully synthesized via wet chemical method. XRD results revealed the single phase nature with the wurtzite structure of the as prepared ZnO nanorods. By only varying the concentration of Hexamethylenetetramine (HMT) in the solution, morphology of ZnO changed from hexagonal facet nanorods to pencil like nanorods and size of nanorods also changed. The band gap of as-synthesized ZnO nanorods was found to increase with increasing the concentration of HMT in the solution. The narrow full-width at half-maximum (FWHM) of the UV emission of PL spectra indicated that the grown ZnO nanorods have high crystal quality and is well matched with the obtained XRD results. These results revealed that the concentration of Hexamethylenetetramine plays a vital role to control the properties of ZnO nanorods.

Heo, Si Nae; Park, Keun Young; Seo, Yong Jun; Ahmed, Faheem; Anwar, M. S.; Koo, Bon Heun

2013-05-01

217

Photochromism of diarylethene single molecules and single crystals.  

PubMed

Photochromism is characterized as a reversible colour change of a chemical species upon photoirradiation. Although vast numbers of photochromic molecules have been so far synthesized, molecules which exhibit thermally irreversible photochromic reactivity are limited within a few families of compounds. Among the thermally irreversible photochromic molecules, diarylethene derivatives are the most promising candidates for applications to opto-electronic devices because of their fatigue resistance, high sensitivity and rapid response. In this review, characteristic photochromic performances of the derivatives, detection and analysis of the photochromic reactions at a single-molecule level and application of the single-crystalline photochromism to molecular machinery will be described. PMID:20959925

Irie, Masahiro

2010-12-01

218

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

219

Single-atom switching in photonic crystals  

NASA Astrophysics Data System (ADS)

We describe the role of first non-Markovian corrections to resonance fluorescence in photonic crystals, using a perturbative expansion of the Heisenberg equations of motion in powers of the atom-field reservoir coupling strength. Non-Markovian effects arise from the rapid variation of the photonic density of states with frequency. Our method recaptures the physics of the photon-atom bound state in the presence of a full photonic band gap. For the anisotropic three-dimensional photonic band gap, it predicts remarkable features in the resonance fluorescence, such as atomic population inversion and switching behavior in a two-level atom for moderate values of the applied laser field. The magnitude of the switching effect depends sensitively on the external laser intensity and its detuning frequency from the atomic transition. The robustness of this effect against nonradiative decay and dephasing mechanisms is also investigated.

Florescu, Marian; John, Sajeev

2001-09-01

220

Studying the magnetic properties of CoSi single crystals  

SciTech Connect

The magnetic properties of CoSi single crystals have been measured in a range of temperatures T = 5.5-450 K and magnetic field strengths H {<=} 11 kOe. A comparison of the results for crystals grown in various laboratories allowed the temperature dependence of magnetic susceptibility {chi}(T) = M(T)/H to be determined for a hypothetical 'ideal' (free of magnetic impurities and defects) CoSi crystal. The susceptibility of this ideal crystal in the entire temperature range exhibits a diamagnetic character. The {chi}(T) value significantly increases in absolute value with decreasing temperature and exhibits saturation at the lowest temperatures studied. For real CoSi crystals of four types, paramagnetic contributions to the susceptibility have been evaluated and nonlinear (with respect to the field) contributions to the magnetization have been separated and taken into account in the calculations of {chi}(T).

Narozhnyi, V. N., E-mail: narozhnyivn@gmail.com; Krasnorussky, V. N. [Russian Academy of Sciences, Vereshchagin Institute for High Pressure Physics (Russian Federation)

2013-05-15

221

Modelling of Heat Transfer in Single Crystal Growth  

E-print Network

An attempt is made to review the heat transfer and the related problems encountered in the simulation of single crystal growth. The peculiarities of conductive, convective and radiative heat transfer in the different melt, solution, and vapour growth methods are discussed. The importance of the adequate description of the optical crystal properties (semitransparency, specular reflecting surfaces) and their effect on the heat transfer is stresses. Treatment of the unknown phase boundary fluid/crystal as well as problems related to the assessment of the quality of the grown crystals (composition, thermal stresses, point defects, disclocations etc.) and their coupling to the heat transfer/fluid flow problems is considered. Differences between the crystal growth simulation codes intended for the research and for the industrial applications are indicated. The problems of the code verification and validation are discussed; a brief review of the experimental techniques for the study of heat transfer and flow structu...

Zhmakin, Alexander I

2014-01-01

222

Textures in Single-Crystal Aluminum Friction Stir Spot Welds  

Microsoft Academic Search

The present article examines the textural features produced during friction stir spot welding of single-crystal aluminum sheet.\\u000a The crystal has the {111} plane perpendicular to the normal direction (ND) of the sheet, and the $$ \\\\left\\\\langle { 1 10} \\\\right\\\\rangle $$ direction parallel to the growth direction (GD). Friction stir spot welding was carried out using a rotation speed of

Toshiya Shibayanagi; Adrian P. Gerlich; Keizo Kashihara; Thomas H. North

2009-01-01

223

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

224

Plane wave simulation of elastic-viscoplastic single crystals  

NASA Astrophysics Data System (ADS)

Despite the large amount of research that has been performed to quantify the high strain rate response of Aluminum, few studies have addressed effects of crystal orientation and subsequent crystal-level microstructure evolution on its high strain rate response. To study orientation effects in single crystal Al, both a constitutive model and novel numerical method have been developed. A plane wave formulation is developed so that materials undergoing anisotropic viscoplastic deformation can be modeled in a thermodynamically consistent framework. Then, a recently developed high strain rate viscoplastic model is extended to include single crystal effects by incorporating higher order crystal-based thermoelasticity, anisotropic plasticity kinetics, and distinguishing influences of forest and parallel dislocation densities. Steady propagating shock waves are simulated for [100], [110], and [111] oriented single crystals and compared to existing experimental wave profile and strength measurements. Finally, influences of initial orientation and peak pressure ranging from 0 to 30 GPa are quantified. Results indicate that orientation plays a significant role in dictating the high rate response of both the wave profile and the resultant microstructure evolution of Al. The plane wave formulation can be used to evaluate microstructure-sensitive constitutive relations in a computationally efficient framework.

Lloyd, J. T.; Clayton, J. D.; Austin, R. A.; McDowell, D. L.

2014-09-01

225

Growth and characterization of 4-methyl benzene sulfonamide single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of 4-methyl benzene sulfonamide (4MBS) were successfully grown from aqueous solution by low temperature solution growth technique. The grown crystal was characterized by single crystal XRD and powder XRD methods to obtain the lattice parameters and the diffraction planes of the crystal. UV-vis-NIR absorption spectrum was used to measure the range of optical transmittance and optical band gap energy. The optical transmission range was measured as 250-1200 nm. FTIR spectral studies were carried out to identify the presence of functional groups in the grown crystal. The thermal behavior of the crystal was investigated from thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC) study. The absence of SHG was noticed by Kurtz and Perry powder technique. The third order NLO behavior of the material was confirmed by measuring the nonlinear optical properties using Z-scan technique and it was found that the crystal is capable of exhibiting saturation absorption and self-defocusing performance.

Thirumalaiselvam, B.; Kanagadurai, R.; Jayaraman, D.; Natarajan, V.

2014-11-01

226

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

227

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

228

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

229

Elastic constants of single crystal Hastelloy X at elevated temperatures  

SciTech Connect

An acoustic time of flight technique is described in detail for measuring the elastic constants of cubic single crystals that allows for the constants to be determined at elevated temperature. Although the overall technique is not new, various aspects of the present work may prove extremely useful to others interested in finding these values, especially for aerospace materials applications. Elastic constants were determined for the nickel based alloy, Hastelloy X from room temperature to 1,000 C. Accurate elastic constants were needed as part of an effort to predict both polycrystal mechanical properties and the nature of grain induced heterogeneous mechanical response. The increased accuracy of the acoustically determined constants resulted in up to a 15% change in the predicted stresses in individual grains. These results indicate that the use of elastic single crystal constants of pure nickel as an approximation for the constants of gas turbine single crystal alloys, which is often done today, is inaccurate.

Canistraro, H.A. [Univ. of Hartford, CT (United States). Dept. of Mechanical and Audio Engineering Technology; Jordan, E.H.; Shi Shixiang [Univ. of Connecticut, Storrs, CT (United States); Favrow, L.H.; Reed, F.A. [United Technologies Research Center, East Hartford, CT (United States)

1998-07-01

230

Shock wave compression of single-crystal forsterite  

Microsoft Academic Search

Hugoniot equation of state measurements have been performed on pure synthetic single-crystal forsterite (Mg2SiO4) in the pressure range 70-160 GPa (0.7-1.6 Mbar). These and earlier data for polycrystalline forsterite are compared with theoretical Hugoniots for the assemblages 2MgO (rocksalt) +SiO2 (stishovite) and MgO (rocksalt) +MgSiO3 (perovskite). The densities attained by single-crystal forsterite at pressures in excess of 120 GPa are

Ian Jackson; Thomas J. Ahrens

1979-01-01

231

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

232

Imaging linear polarimetry using a single ferroelectric liquid crystal modulator.  

PubMed

In the field of polarimetry, ferroelectric liquid crystal cells are mostly used as bistable polarization rotators suitable to analyze crossed polarizations. This paper shows that, provided such a cell is used at its nominal wavelength and correctly driven, its behavior is close to that of a tunable half-wave plate, and it can be used with much benefit in lightweight imaging polarimetric setups. A partial Stokes polarimeter using a single digital video camera and a single ferroelectric liquid crystal modulator is designed and implemented for linear polarization analysis. Polarization azimuthal angle and degree of linear polarization are available at 150 frames per second with a good accuracy. PMID:20820209

Gendre, Luc; Foulonneau, Alban; Bigué, Laurent

2010-09-01

233

Positron annihilation study of defects in electron-irradiated single crystal zinc oxide  

NASA Astrophysics Data System (ADS)

Pressurized melt grown zinc oxide (ZnO) single crystals purchased from Cermet Inc. were irradiated by 2MeV electrons with fluence of 6x1017cm-2. Isochronal annealing from 100°C-800°C was performed on the crystals under argon and air ambience. Variable Energy Doppler Broadening Spectroscopy (VEDBS) was carried out on both the as-grown and the irradiated samples at each annealing step. The migration, agglomeration and annealing of grown-in and irradiated-introduced defects were studied. It was observed that the grown-in vacancy-type defects concentration decreased at 300°C and 600 °C. For the irradiated sample annealed in argon, the positron trapping vacancy-type defect concentration decreased at 300°C and 600°C. Further annealing the as-grown and irradiated samples in argon increased the S parameter further. For the irradiated sample annealed in air, the vacancy-type defect concentration decreases at 300°C and 700°C.

To, C. K.; Yang, B.; Beling, C. D.; Fung, S.; Ling, C. C.; Gong, M.

2011-01-01

234

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

235

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

236

perovskite: a single-crystal X-ray diffraction study  

NASA Astrophysics Data System (ADS)

Magnesium silicate perovskite is the predominant phase in the Earth's lower mantle, and it is well known that incorporation of iron has a strong effect on its crystal structure and physical properties. To constrain the crystal chemistry of (Mg, Fe)SiO3 perovskite more accurately, we synthesized single crystals of Mg0.946(17)Fe0.056(12)Si0.997(16)O3 perovskite at 26 GPa and 2,073 K using a multianvil press and investigated its crystal structure, oxidation state and iron-site occupancy using single-crystal X-ray diffraction and energy-domain Synchrotron Mössbauer Source spectroscopy. Single-crystal refinements indicate that all iron (Fe2+ and Fe3+) substitutes on the A-site only, where based on Mössbauer spectroscopy. Charge balance likely occurs through a small number of cation vacancies on either the A- or the B-site. The octahedral tilt angle ( ?) calculated for our sample from the refined atomic coordinates is 20.3°, which is 2° higher than the value calculated from the unit-cell parameters ( a = 4.7877 Å, b = 4.9480 Å, c = 6.915 Å) which assumes undistorted octahedra. A compilation of all available single-crystal data (atomic coordinates) for (Mg, Fe)(Si, Al)O3 perovskite from the literature shows a smooth increase of ? with composition that is independent of the nature of cation substitution (e.g., or substitution mechanism), contrary to previous observations based on unit-cell parameter calculations.

Sinmyo, Ryosuke; Bykova, Elena; McCammon, Catherine; Kupenko, Ilya; Potapkin, Vasily; Dubrovinsky, Leonid

2014-06-01

237

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

238

Highly enhanced acetone sensing performances of porous and single crystalline ZnO nanosheets: high percentage of exposed (100) facets working together with surface modification with Pd nanoparticles.  

PubMed

Porous and single crystalline ZnO nanosheets, which were synthesized by annealing hydrozincite Zn(5)(CO(3))(2)(OH)(6) nanoplates produced with a water/ethylene glycol solvothermal method, are used as building blocks to construct functional Pd-ZnO nanoarchitectures together with Pd nanoparticles based on a self-assembly approach. Chemical sensing performances of the ZnO nanosheets were investigated carefully before and after their surface modification with Pd nanoparticles. It was found that the chemical sensors made with porous ZnO nanosheets exhibit high selectivity and quick response for detecting acetone, because of the 2D ZnO nanocrystals exposed in (100) facets at high percentage. The performances of the acetone sensors can be further improved dramatically, after the surfaces of ZnO nanosheets are modified with Pd nanoparticles. Novel acetone sensors with enhanced response, selectivity and stability have been fabricated successfully by using nanoarchitectures consisting of ZnO nanosheets and Pd nanoparticles. PMID:22853192

Xiao, Yuanhua; Lu, Lingzhen; Zhang, Aiqin; Zhang, Yonghui; Sun, Li; Huo, Lei; Li, Feng

2012-08-01

239

Growth and spectroscopic properties of samarium oxalate single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of samarium oxalate decahydrate were synthesized using single diffusion gel technique and the conditions influencing the size, shape and quality were optimized. Highly transparent crystals of size 3×2×1 mm3 with a well defined hexagonal morphology were grown during a time period of two weeks. X ray powder diffraction analysis revealed that the grown crystals crystallize in the monoclinic system with space group P21/c and the proposed chemical formula and linkage of water molecules were confirmed using thermogravimetric analysis. The various functional groups of the oxalate ligand and the water of crystallization were identified by Fourier transform infrared spectroscopy. Spectroscopic investigations such as electric dipole transition probability, magnetic dipole transition probability and branching ratios of all possible transitions from 4G5/2 level of Sm3+ ions were estimated from the absorption spectra using JO theory. The spectroscopic analysis suggested that the crystal has a strong and efficient orange red emission. This is confirmed from the photoluminescence spectrum with a wavelength peak at 595 nm and hence this promising emission can be effectively used for optical amplification.

Vimal, G.; Mani, Kamal P.; Jose, Gijo; Biju, P. R.; Joseph, Cyriac; Unnikrishnan, N. V.; Ittyachen, M. A.

2014-10-01

240

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

241

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

242

Characterization of phosphoric acid doped TGS single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of phosphoric acid (H3PO4) doped triglycine sulfate (TGSP) are grown from aqueous solution containing 10-50 mol% of H3PO4. Large sized crystals of dimension (70 mm×40 mm×25 mm) suitable for IR detector applications are obtained with 20 mol% 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 glycinium ions in the doped TGSP crystals, which is due to the low incorporation of H3PO4 into the TGS crystal lattice. The dielectric properties TGSP crystals measured in the temperature range 27-65°C and in frequency range 102-105 Hz show a broad transition, and the peak dielectric constant values are reduced with increasing H3PO4 concentration. Hysteresis loops with high coercive fields are observed up to 20 mol% of H3PO4. At a higher concentration, double loops are observed due to the polarization switching inhibition by H3PO4 molecules. Dopant concentration is found to have a marginal influence on the spontaneous polarization of the TGSP crystals.

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

2004-03-01

243

Vacancy-Formation Energy and Entropy in Magnesium Single Crystals  

Microsoft Academic Search

Macroscopic thermal dilatation coefficients as well as those of the lattice have been precisely measured along principal crystallographic directions of magnesium single crystals in the temperature range between room temperature and 650°C. The vacancy concentration was thus obtained as a function of temperature and it reached the value of 72×10-5 in the neighborhood of the melting point. An appreciable anisotropy

C. Janot; D. Malléjac; B. George

1970-01-01

244

Tutorial: Organic Single Crystals 101 Prof. Vitaly Podzorov  

E-print Network

11 Tutorial: Organic Single Crystals 101 Prof. Vitaly Podzorov Institute for Advanced Materials://www.physics.rutgers.edu/~podzorov/index.php http://iamdn.rutgers.edu/ Fall MRS 2012 Nov. 25, 2012 (Boston, MA) Fall MRS-2012 Tutorial (V. Podzorov) #12;22 This tutorial and detailed technical notes can be downloaded from: http

Glashausser, Charles

245

Anisotropic continuum damage modeling for single crystals at high temperatures  

Microsoft Academic Search

In single crystals, the process of creep damage is generally anisotropic. Indeed, the damage evolution does not only depend on the loading conditions, but also on the lattice orientation. And the current state of damage has an anisotropic influence on the effective stress state, so that it is represented by a tensorial damage variable. Based on the continuum damage mechanics

Weidong Qi; Albrecht Bertram

1999-01-01

246

Cyclic plasticity of nickel single crystals at elevated temperatures  

Microsoft Academic Search

Single slip oriented nickel crystals have been cyclically deformed at deformation temperatures between 293 K and 900 K until saturation of the stress amplitude. Persistent slip bands (PSBs) with a typical ladder-like dislocation substructure occur at temperatures up to 800 K. At 600 K and 750 K the measured cyclic stress-strain curves (CSSCs) exhibit extended ranges in which the saturation

J. Bretschneider; C. Holste; B. Tippelt

1997-01-01

247

TOPICAL REVIEW: Organic field-effect transistors using single crystals  

NASA Astrophysics Data System (ADS)

Organic field-effect transistors using small-molecule organic single crystals are developed to investigate fundamental aspects of organic thin-film transistors that have been widely studied for possible future markets for 'plastic electronics'. In reviewing the physics and chemistry of single-crystal organic field-effect transistors (SC-OFETs), the nature of intrinsic charge dynamics is elucidated for the carriers induced at the single crystal surfaces of molecular semiconductors. Materials for SC-OFETs are first reviewed with descriptions of the fabrication methods and the field-effect characteristics. In particular, a benchmark carrier mobility of 20-40 cm2 Vs-1, achieved with thin platelets of rubrene single crystals, demonstrates the significance of the SC-OFETs and clarifies material limitations for organic devices. In the latter part of this review, we discuss the physics of microscopic charge transport by using SC-OFETs at metal/semiconductor contacts and along semiconductor/insulator interfaces. Most importantly, Hall effect and electron spin resonance (ESR) measurements reveal that interface charge transport in molecular semiconductors is properly described in terms of band transport and localization by charge traps.

Hasegawa, Tatsuo; Takeya, Jun

2009-04-01

248

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

249

Anisotropic properties of molybdenum disulfide single crystal in catalysis  

Microsoft Academic Search

When a wafer of molybdenum disulfide single crystal was mounted in a reactor with the basal plane of sulfur exposed and a similar wafer cut into small pieces was mounted in a twin reactor with a large edge surface area of coordinatively unsaturated molybdenum ions exposed, the cut, but not the uncut, catalyst was active for the cis-trans isomerization of

T. Okuhara; K. Tanaka

1978-01-01

250

Birefringence induced by uniaxial stress in cadmium telluride single crystals  

Microsoft Academic Search

The birefringence induced by uniaxial stress in cadmium telluride single crystals was investigated. Static uniaxial compression was applied along the (100), (110), (111) and (112) directions. It was found that n\\/sub \\/\\/\\/-nperpendicular to changes sign near the absorption edge. The position of the inversion point depends on the direction of stress and the direction of light. The components of the

W. Wardzyoski

1970-01-01

251

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

252

The magnetization process in hexagonal ferromagnetic and ferrimagnetic single crystals  

Microsoft Academic Search

Neel's 'theory of phases' is used to study the magnetization process in hexagonal ferromagnetic and ferrimagnetic single-crystal ellipsoids for which the six fold contribution to the magnetocrystalline anisotropy cannot be neglected. Simultaneous equations are presented, the solution of which yields the intensity and orientation of the mean sample magnetization and the various orientations of the saturation magnetization in the domains,

R. R. Birss; D. J. Martin

1975-01-01

253

Polarized superradiance from delocalized exciton transitions in tetracene single crystals  

Microsoft Academic Search

Polarized superradiant emission and exciton delocalization in tetracene single crystals are reported. Polarization-, time-, and temperature-resolved spectroscopies evidence the complete polarization of the zero-phonon line of the intrinsic tetracene emission from both the lower ( F state) and the upper (thermally activated) Davydov excitons. The superradiance of the F emission is substantiated by a nearly linear decrease in the radiative

A. Camposeo; M. Polo; S. Tavazzi; L. Silvestri; P. Spearman; R. Cingolani; D. Pisignano

2010-01-01

254

Single Crystal SiC Microhotplate Conductometric Chemical Sensor Arrays  

Microsoft Academic Search

Microhotplates are miniature (typically ~100µm on a side) micromachined devices with integrated heaters, temperature sensors and film resistance sensors. With their low power consumption, millisecond thermal response times and small size (allowing compact microsensor arrays), microhotplates are versatile chemical sensor platforms (1) and powerful materials deposition and characterization tools (2). When fabricated from single crystal silicon carbide, the mechanical support,

Richard Mlcak; George Whitfield; Harry Tuller

255

Nanoindentation creep of single-crystal tungsten and gallium arsenide  

Microsoft Academic Search

An extensive study of indentation creep on the nanometre scale has been made on single-crystal indium, tungsten and gallium arsenide. We use the force modulation technique which gives a direct measure of contact stiffness and, being insensitive to thermal drift, allows the accurate observation of creep in small indents to be carried out over long time periods: We show that

S. A. Syed Asif; J. B. Pethica

1997-01-01

256

Direct Bonding of LiTaO3 Single Crystals  

Microsoft Academic Search

A new fabrication method for combining lithium tantalate single crystals by direct bonding without using bonding agents has been developed. The bonded interface was found to be very uniform, and bonding on an atomic scale was achieved in spite of a relatively low heat-treatment temperature of 350°C. This method is very promising for realizing new stacked structures and new fabrication

Yoshihiro Tomita; Masato Sugimoto; Kazuo Eda; Tetsuyuki Okano

1994-01-01

257

Elastic constants of single crystal Hastelloy X at elevated temperatures  

Microsoft Academic Search

An acoustic time of flight technique is described in detail for measuring the elastic constants of cubic single crystals that allows for the constants to be determined at elevated temperature. Although the overall technique is not new, various aspects of the present work may prove extremely useful to others interested in finding these values, especially for aerospace materials applications. Elastic

Howard A. Canistraro; Eric H. Jordan; Shi Shixiang; Leroy H. Favrow; Francis A. Reed

1998-01-01

258

Oxidation behavior of single crystal TMS82+ superalloy in air  

Microsoft Academic Search

The oxidation behavior of the single crystal Ni-based superalloy TMS-82+ was studied under cyclic condition at 900 and 1 000 ? for 200 h in air. The oxidation kinetics for the superalloy at both exposure temperatures was explained by the subparabolic relationship. The results show that increasing the exposure temperature from 900 to 1 000 ?, the amounts of ?-Al2O3,

WU Ying; SONG Gui-ming; ZHOU Shao-xiong; T. NARITA

259

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

260

Scalable synthesis of graphene on single crystal Ir(111) films  

NASA Astrophysics Data System (ADS)

We have investigated single crystal Ir(111) films grown heteroepitaxially on Si(111) wafers with yttria-stabilized zirconia (YSZ) buffer layers as possible substrates for an up-scalable synthesis of graphene. Graphene was grown by chemical vapor deposition (CVD) of ethylene. As surface analytical techniques we have used scanning tunneling microscopy (STM), low-energy electron diffraction, scanning electron microscopy, and atomic force microscopy. The mosaic spread of the metal films was below 0.2° similar to or even below that of standard Ir bulk single crystals, and the films were basically twin-free. The film surfaces could be improved by annealing so that they attained the perfection of bulk single crystals. Depending on the CVD conditions a lattice-aligned graphene layer or a film consisting of different rotational domains were obtained. STM data of the non-rotated phase and of the phases rotated by 14° and 19° were acquired. The quality of the graphene was comparable to graphene grown on bulk Ir(111) single crystals.

Zeller, Patrick; Dänhardt, Sebastian; Gsell, Stefan; Schreck, Matthias; Wintterlin, Joost

2012-10-01

261

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

262

Intense intrashell luminescence of Eu-doped single ZnO nanowires at room temperature by implantation created Eu-Oi complexes.  

PubMed

Successful doping and excellent optical activation of Eu(3+) ions in ZnO nanowires were achieved by ion implantation. We identified and assigned the origin of the intra-4f luminescence of Eu(3+) ions in ZnO by first-principles calculations to Eu-Oi complexes, which are formed during the nonequilibrium ion implantation process and subsequent annealing at 700 °C in air. Our targeted defect engineering resulted in intense intrashell luminescence of single ZnO:Eu nanowires dominating the photoluminescence spectrum even at room temperature. The high intensity enabled us to study the luminescence of single ZnO nanowires in detail, their behavior as a function of excitation power, waveguiding properties, and the decay time of the transition. PMID:24972185

Geburt, Sebastian; Lorke, Michael; da Rosa, Andreia L; Frauenheim, Thomas; Röder, Robert; Voss, Tobias; Kaiser, Uwe; Heimbrodt, Wolfram; Ronning, Carsten

2014-08-13

263

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

264

Novel single-mode and polarization maintaining photonic crystal fiber  

NASA Astrophysics Data System (ADS)

In this paper, we present and propose a novel structure for improved birefringence and single-mode propagation condition photonic crystal fiber (PCF) in a broad range of wavelength. The birefringence of the fundamental mode and single mode property in such a PCF is numerically estimated by employing full vector finite element method (FVFEM) and anisotropic perfectly matched layers (APML). The simulation results illustrate that we can achieve a high birefringence and perfect single-mode condition by employing silica-filled into one-line elliptical air holes parallel to x-axis and rotated by an angle. Obviously, the proposed PCF is quite useful for optical devices.

Yin, Aihan; Xiong, Lei

2014-11-01

265

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

266

Single crystal diamond probes for atomic-force microscopy  

NASA Astrophysics Data System (ADS)

Results obtained in the development and testing of high-strength, chemically inert, and sharply pointed single crystal diamond probes for atomic-force microscopy are presented. The probes were fabricated on the basis of pyramidal diamond single crystals produced by selective oxidation of polycrystalline films grown by chemical vapor deposition. A procedure was developed for attachment of single needles to cantilevers of silicon probes. A transmission electron microscope was used to find that the apical angle of the pyramidal diamond crystallites is about 10° and the radius of curvature of the apex of the diamond crystallite is 2-10 nm. It is shown for the example of two test samples (graphite surface and DNA molecules) that the diamond probes can be effectively used in atomic-force microscopy and make it possible to improve the image quality compared with standard silicon probes.

Tuyakova, F. T.; Obraztsova, E. A.; Klinov, D. V.; Ismagilov, R. R.

2014-07-01

267

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

268

Investigations into the impact of various substrates and ZnO ultra thin seed layers prepared by atomic layer deposition on growth of ZnO nanowire array  

PubMed Central

The impact of various substrates and zinc oxide (ZnO) ultra thin seed layers prepared by atomic layer deposition on the geometric morphology of subsequent ZnO nanowire arrays (NWs) fabricated by the hydrothermal method was investigated. The investigated substrates included B-doped ZnO films, indium tin oxide films, single crystal silicon (111), and glass sheets. Scanning electron microscopy and X-ray diffraction measurements revealed that the geometry and aligment of the NWs were controlled by surface topography of the substrates and thickness of the ZnO seed layers, respectively. According to atomic force microscopy data, we suggest that the substrate, fluctuate amplitude and fluctuate frequency of roughness on ZnO seed layers have a great impact on the alignment of the resulting NWs, whereas the influence of the seed layers' texture was negligible. PMID:22759838

2012-01-01

269

Investigations into the impact of various substrates and ZnO ultra thin seed layers prepared by atomic layer deposition on growth of ZnO nanowire array  

NASA Astrophysics Data System (ADS)

The impact of various substrates and zinc oxide (ZnO) ultra thin seed layers prepared by atomic layer deposition on the geometric morphology of subsequent ZnO nanowire arrays (NWs) fabricated by the hydrothermal method was investigated. The investigated substrates included B-doped ZnO films, indium tin oxide films, single crystal silicon (111), and glass sheets. Scanning electron microscopy and X-ray diffraction measurements revealed that the geometry and aligment of the NWs were controlled by surface topography of the substrates and thickness of the ZnO seed layers, respectively. According to atomic force microscopy data, we suggest that the substrate, fluctuate amplitude and fluctuate frequency of roughness on ZnO seed layers have a great impact on the alignment of the resulting NWs, whereas the influence of the seed layers' texture was negligible.

Ding, JN; Liu, YB; Tan, CB; Yuan, NY

2012-07-01

270

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

271

Subsurface Stress Fields In Single Crystal (Anisotropic) Contacts  

NASA Technical Reports Server (NTRS)

Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is , presented, for evaluating the subsurface stresses in the elastic half-space, using a complex potential method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis. Effects of crystal orientation on stress response and fatigue life are examined.

Arakere, Nagaraj K.; Knudsen, Erik C.; Duke, Greg; Battista, Gilda; Swanson, Greg

2004-01-01

272

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

273

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

274

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

275

Epitaxial growth, structure, and magnetism of epitaxial Ni80Fe20 single-crystal, bicrystal, and quad-crystal films  

E-print Network

Epitaxial growth, structure, and magnetism of epitaxial Ni80Fe20 single-crystal, bicrystal epitaxy MBE growth and structural and magnetic characterizations of high-quality single-crystal, bi the conclusion is made. II. SAMPLE PREPARATION AND MEASUREMENTS The crystal growth was carried out in a MBE

Huang, Jung-Chun

276

Single-crystal Si formed on amorphous substrate at low temperature by nanopatterning and nickel-induced lateral crystallization  

E-print Network

Single-crystal Si formed on amorphous substrate at low temperature by nanopatterning and nickel-induced lateral crystallization Jian Gu and Stephen Y. Chou NanoStructure Laboratory, Department of Electrical, Utah 84020 Received 11 April 2002; accepted for publication 7 June 2002 Single-crystal silicon has been

277

Electrical characteristics of palladium Schottky contacts to hydrogen peroxide treated hydrothermally grown ZnO  

Microsoft Academic Search

The formation of Schottky barrier contacts to hydrogen peroxide treated ZnO has been investigated. Low resistivity hydrothermally grown single crystal ZnO wafers of n-type were used. Pd contacts deposited on organic solvent cleaned O face (0001) showed Ohmic behavior, while on the H2O2 treated O face up to nine orders of magnitude in rectification of the current was obtained for

R. Schifano; E. V. Monakhov; U. Grossner; B. G. Svensson

2007-01-01

278

A new material for single crystal modulators: BBO  

NASA Astrophysics Data System (ADS)

Single crystal photo-elastic modulators (SCPEM) are based on a single piezo-electric crystal which is electrically excited on a resonance frequency such that the resulting resonant oscillation causes a modulated artificial birefringence due to the photo-elastic effect. Polarized light experience in such a crystal a strong modulation of polarization, which, in connection with a polarizer, can be used for Q-switching of lasers with pulse repetition frequencies in the range of 100- 1000 kHz. A particularly advantageous configuration is possible with crystals from the symmetry class 3m. Besides LiTaO3 and LiNbO3, both already well explored as SCPEM-materials, we introduce now BBO, which offers a very low absorption in the near infrared region and is therefore particularly suited for Q-switching of solid state lasers. We demonstrate first results of such a BBO-modulator with the dimensions 8.6 x 4.05 x 4.5mm in x-, y-, z- direction, which offers a useful resonance and polarization modulation at 131.9 kHz. Since the piezo-electric effect is small, the voltage amplitude for achieving Q-switching for an Nd:YAG-laser is expected to be in the range of 100V. Nevertheless it is a simple and robust device to achieve Q-switching with a high fixed repetition rate for high power solid state lasers.

Bammer, F.; Schumi, T.; Petkovsek, R.

2011-06-01

279

Current path simulation of Bi-2212 phase superconducting single crystals  

NASA Astrophysics Data System (ADS)

In the oxide superconductor with layered structure, the superconducting currents flow in the Cu-O 2 plane that is parallel to the a- b axis. The critical current Ic of Bi 2Sr 2CaCu 2O x (Bi-2212) single crystals measured by a four-probe method did not increase linearly with increasing the thickness of the crystal. The saturated Ic value of the crystals was about 2.8 A. The results meant that the current flow in the a- b plane is different from that in c-axis in the oxide superconductor. In the Cu-O 2 planes that are parallel to the a- b plane, the superconducting currents flow in a conventional conduction system, whereas between the Cu-O 2 planes that are perpendicular to the a- b plane, they flow by tunneling mechanism. We assumed the current path in a single crystal, and calculated the Ic by the superconducting current simulation. The results indicated that the superconducting current between the Cu-O 2 planes decreased by 2.5% in every 1 ?m.

Hara, M.; Imao, H.; Matsumoto, K.

2007-10-01

280

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

281

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

282

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

283

Averaged effective pinning potential in YBCO single crystals near Tc  

NASA Astrophysics Data System (ADS)

The dynamics of magnetic flux trapped in low dc magnetic fields (of the order of the Earth's field) was for the first time studied experimentally in single-crystal YBCO samples with unidirectional twin boundaries in the temperature range near Tc (0.8 < T/Tc < 0.99). Strong pinning in the system of unidirectional planar defects was demonstrated, and a significant deviation from monotonous behavior was established for the averaged effective pinning potential Up(T) for the trapped flux of low density. In order to compare different methods of Jc determination, the field dependences of the magnetization loop width M(H), which are related to the effective pinning and Jc, were obtained, and resistive measurements on microbridges made from the same single crystals were carried out.

Monarkha, V. Yu.; Sivakov, A. G.; Timofeev, V. P.

2014-09-01

284

Challenges for Single-crystal (SX) Crack Cladding  

NASA Astrophysics Data System (ADS)

The formation of cracks in single-crystal (SX) turbine blades is a common problem for aero-engines. If cracks are located under the tip-area, the blade-repair is not possible. Anew method to repair these cracks is to clad with single-crystal-technology.To reduce the loss of material and working time,notches are used to remove the affected crack zone. The usednotch geometries must be weldable and also permit the material solidification in the same oriented plane as the original microstructure. For that, a thermal gradient has to be introduced in order to guide the grain growth. The process characteristics of laser cladding, such as small local heat input and controlled material supply, make it an efficient process to fill the notch. However, there are challenges to achieve a SX structure without cracks and pores. The unstable energy distribution may result in a polycrystalline structure. Current achievements and further challenges are presented in this paper.

Rottwinkel, Boris; Schweitzer, Luiz; Noelke, Christian; Kaierle, Stefan; Wesling, Volker

285

Investment casting of NiAl single-crystal alloys  

NASA Astrophysics Data System (ADS)

Significant progress has been made in the understanding of solidification conditions, microstructure evolution, and defect formation during investment casting of NiAl single crystals. The high liquidus temperatures of NiAl alloys result in a larger dendrite arm spacing than is found in superalloy René N5. Because of their higher thermal conductivities, NiAl alloys have higher cooling rates and lower temperature gradients during solidification than René N5. These differences give NiAl alloys a lower tendency to form freckles and a higher tendency to form equiaxed grains. However, with the aid of process modeling, single crystals of various shapes of NiAl alloys have been produced.

Yu, K. O.; Oti, J. A.; Walston, W. S.

1993-05-01

286

Resonant photoemission in single-crystal black phosphorus  

Microsoft Academic Search

Resonant photoemission in single-crystal black phosphorus has been reinvestigated in detail by high-resolution spectroscopy. Partial-yield, valence-band, and constant-initial-state spectra were measured in the 2p core-exciton excitation region. We have confirmed two types of resonances at the 2p core threshold: one is a strong core-exciton-induced resonance with two final valence holes and the other is a weak Fano-type resonance. The Fano-type

M. Taniguchi; J. Ghijsen; R. L. Johnson; S. Suga; Y. Akahama; S. Endo

1989-01-01

287

Deformation of FeAl single crystals at high temperatures  

Microsoft Academic Search

Single crystals of the intermetallic compound FeAl with the CsCl structure have been deformed in compression at temperatures between 470 and 1000 K to study the slip geometry and the dislocation arrangements in this material at high temperatures. At temperatures below 0·44 of the melting temperature, Tm, slip occurs on the {110}?111? systems, while at 0·44Tm, the transitions in the

Y. Umakoshi; M. Yamaguchi

1980-01-01

288

Electrical conductivity of olivine single crystals at high temperature  

Microsoft Academic Search

The electrical conductivity in three single crystal specimens of olivine (fayalite mole %; 7.4, 8.4 and 12.6) is measured along the three crystallographic orientations in the temperature range of 600° to 1200°K. There are two different mechanisms with different activation energy for electrical conduction; presumably the impurity (Fe) conduction is predominant above 800°K and extrinsic conduction is predominant below 800°K.

Yoji Kobayashi; Hiroshi Maruyama

1971-01-01

289

Plastic deformation of nickel single crystals at low temperatures  

Microsoft Academic Search

Single crystals of nickel (purities 99.98% and 99.4%) have been deformed in tension at various temperatures between 4.2°K and 300°K. Shear stress-shear strain relations have been determined as well as the reversible change of flow stress with temperature. The work-hardening parameters obtained are discussed in terms of dislocation theory that has been developed mainly on the basis of data on

Peter Haasen

1958-01-01

290

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

291

Electron spectroscopy of single crystal and polycrystalline cerium oxide surfaces  

Microsoft Academic Search

Valence band photoemission (XPS), valence band electron energy loss spectroscopy (EELS), Ce3d and 4d XPS, O1s XPS and O1s X-ray absorption (XAS) have been investigated for oxidized and sputtered single crystal CeO2 films and for oxidized Ce foil. Features were identified that distinguish between the Ce4+ or Ce3+ oxidation states. Ce4+ was identified by the highest binding energy peaks in

D. R Mullins; S. H Overbury; D. R Huntley

1998-01-01

292

ELECTRICAL CONDUCTION IN SINGLE-CRYSTAL ALUMINUM THIN FILMS  

Microsoft Academic Search

Electrical conduction in thin (400?1500 Å) single-crystal aluminum films vacuum evaporated on NaCl substrates is explained by a simple model and verified by experimental results. The resistivity of the inter-island boundaries is accounted for by considering the film structure as a metal—insulator matrix and calculating its equivalent resistivity. An unambiguous comparison can then be made with the Fuchs—Sondheimer theory of

T. S. Jayadevaiah; Robert E. Kirby

1969-01-01

293

Carrier doping and interlayer coupling in HTSC single crystals  

Microsoft Academic Search

Experimental results of the effect of carrier doping on the irreversibility lines in (La, Sr)2CuO4-delta and Bi2Sr2CaCu2O8+delta single crystals are summarized. As a function of Sr or oxygen contents, systematic and dramatic widening of the irreversible regions in the B - T phase diagram was observed in both systems. The present study suggests the critical importance of carrier concentration which

K. Kishio; J. Shimoyama; T. Kimura; Y. Kotaka; K. Kitazawa; K. Yamafuji; Q. Li; M. Suenaga

1994-01-01

294

Anisotropy of electronic distribution in a cobalt disilicide single crystal  

NASA Astrophysics Data System (ADS)

An experimental and theoretical analysis of cobalt disilicide Compton profiles is presented. The measurements along [100], [110] and [111] directions of single crystal CoSi 2 are performed with use of synchrotron radiation (59.38 keV). There is a good overall agreement between experimental and theoretical profile anisotropies, obtained from a self consistent linear-muffin-tin-orbitals band structure calculation. The slight difference of observed structures is discussed in terms of d-type bonds.

Bellin, Ch.; Loupias, G.; Manuel, A. A.; Jarlborg, T.; Sakurai, Y.; Tanaka, Y.; Shiotani, N.

1995-11-01

295

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

296

Constitutive modelling of single crystal and directionally solidified superalloys  

NASA Technical Reports Server (NTRS)

Successful attempts were made to model the deformation behavior of nickel base superalloys to be used in gas turbine engines based on both a macroscopic constitutive model and a micromechanical formulation based on crystallographic slip theory. These models were programmed as FORTRAN subroutines, are currently being used to simulate thermomechanical loading predictions expected at the fatigue critical locations on a single crystal turbine blade. Such analyses form a natural precursor to the application of life prediction methods to gas turbine airfoils.

Walker, Kevin P.; Jordan, Eric H.

1987-01-01

297

Pockels effect in yttrium aluminum borate single crystals  

Microsoft Academic Search

Experimental measurements of linear electro-optical coefficients are reported for YAl3(BO3)4 (YAB) single crystals for the two principal tensor components xyz and yyy at the wavelength of a CW semiconducting GaAlAs laser emitting at 1040 nm. We have found the values of the Pockels coefficients\\u000a to be equal to 0.21 ± 0.06 and 0.56 ± 0.08 pm\\/V for 123 and 222

A. H. Reshak; A. Majchrowski; W. Imiolek

2008-01-01

298

Luminescent properties of CdI2 single crystals  

Microsoft Academic Search

The paper deals with the results of studies in luminescent properties of CdI2 single crystals in natural and polarized light. The existence of several bands of intrinsic emission was established. The emission band of 480 nm is dominant within a temperature range of 200-150 K, whereas that of 550 nm is effective at temperatures below 150 K. Possible reasons for

I. M. Bolesta

1976-01-01

299

Interferometric studies of domain structures in potassium niobate single crystals  

Microsoft Academic Search

Interferometric studies of domain structures in KNbO3 single crystals, grown by using excess of K2CO3 as a flux are reported. The surface deformations produced on the pseudocubic (001) planes by the stable patterns of 90°, 60° and 180° domains have been studied and discussed. If the observed plane is not the plane of the shear, the 90° domains are inclined

K G Deshmukh; S G Ingle

1971-01-01

300

Primary creep in single crystal superalloys: Origins, mechanisms and effects  

Microsoft Academic Search

Creep deformation of the CMSX-4 nickel-base single crystal superalloy is studied in the range 750–850°C. Emphasis is placed on elucidating the factors causing primary creep when the tensile stress is orientated within 20°C of the technologically important ?001? direction. It is demonstrated unambiguously that primary creep occurs only if a threshold stress of approximately 500MPa is exceeded; thereafter the accumulated

C. M. F. Rae; R. C. Reed

2007-01-01

301

Journal of Crystal Growth 304 (2007) 114117 Single crystal growth of YbRh2Si2 using Zn flux  

E-print Network

Journal of Crystal Growth 304 (2007) 114�117 Single crystal growth of YbRh2Si2 using Zn flux-temperature solution technique, using Zn flux and followed by a decanting process. As opposed from the crystals growth: A1. Growth from high-temperature solutions; A1. Single crystal; B2. YbRh2Si2 1. Introduction YbRh2Si

Broholm, Collin Leslie

302

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

303

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

304

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

305

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

306

Monitoring lidocaine single-crystal dissolution by ultraviolet imaging.  

PubMed

Dissolution critically affects the bioavailability of Biopharmaceutics Classification System class 2 compounds. When unexpected dissolution behaviour occurs, detailed studies using high information content technologies are warranted. In the present study, an evaluation of real-time ultraviolet (UV) imaging for conducting single-crystal dissolution studies was performed. Using lidocaine as a model compound, the aim was to develop a setup capable of monitoring and quantifying the dissolution of lidocaine into a phosphate buffer, pH 7.4, under stagnant conditions. A single crystal of lidocaine was placed in the quartz dissolution cell and UV imaging was performed at 254 nm. Spatially and temporally resolved mapping of lidocaine concentration during the dissolution process was achieved from the recorded images. UV imaging facilitated the monitoring of lidocaine concentrations in the dissolution media adjacent to the single crystals. The concentration maps revealed the effects of natural convection due to density gradients on the dissolution process of lidocaine. UV imaging has great potential for in vitro drug dissolution testing. PMID:21387316

Østergaard, Jesper; Ye, Fengbin; Rantanen, Jukka; Yaghmur, Anan; Larsen, Susan Weng; Larsen, Claus; Jensen, Henrik

2011-08-01

307

Modeling single-crystal microstructure evolution due to shock loading  

NASA Astrophysics Data System (ADS)

An existing high strain rate viscoplastic (HSRVP) model is extended to address single-crystal anisotropic, elastic-plastic material response and is implemented into a steady plastic wave formulation in the weak shock regime. The single-crystal HSRVP model tracks the nucleation, multiplication, annihilation, and trapping of dislocations, as well as thermally activated and phonon drag limited glide kinetics. The steady plastic wave formulation is used to model the elastic-plastic response with respect to a propagating longitudinal wave, and assumes that the magnitudes of quasi-transverse waves are negligible. This steady wave analysis does not require specification of artificial viscosity, which can give rise to spurious dissipative effects. The constitutive model and its numerical implementation are applied to single-crystal pure Al and results are compared with existing experimental data. Dislocation density evolution, lattice reorientation, and macroscopic velocity-time histories are tracked for different initial orientations subjected to varying peak shock pressures. Results suggest that initial material orientation can significantly influence microstructure evolution, which can be captured using the modified Taylor factor.

Lloyd, J. T.; Clayton, J. D.; Austin, R. A.; McDowell, D. L.

2014-05-01

308

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

309

Single crystal plasticity by modeling dislocation density rate behavior  

SciTech Connect

The goal of this work is to formulate a constitutive model for the deformation of metals over a wide range of strain rates. Damage and failure of materials frequently occurs at a variety of deformation rates within the same sample. The present state of the art in single crystal constitutive models relies on thermally-activated models which are believed to become less reliable for problems exceeding strain rates of 10{sup 4} s{sup -1}. This talk presents work in which we extend the applicability of the single crystal model to the strain rate region where dislocation drag is believed to dominate. The elastic model includes effects from volumetric change and pressure sensitive moduli. The plastic model transitions from the low-rate thermally-activated regime to the high-rate drag dominated regime. The direct use of dislocation density as a state parameter gives a measurable physical mechanism to strain hardening. Dislocation densities are separated according to type and given a systematic set of interactions rates adaptable by type. The form of the constitutive model is motivated by previously published dislocation dynamics work which articulated important behaviors unique to high-rate response in fcc systems. The proposed material model incorporates thermal coupling. The hardening model tracks the varying dislocation population with respect to each slip plane and computes the slip resistance based on those values. Comparisons can be made between the responses of single crystals and polycrystals at a variety of strain rates. The material model is fit to copper.

Hansen, Benjamin L [Los Alamos National Laboratory; Bronkhorst, Curt [Los Alamos National Laboratory; Beyerlein, Irene [Los Alamos National Laboratory; Cerreta, E. K. [Los Alamos National Laboratory; Dennis - Keller, D. [Los Alamos National Laboratory

2010-12-23

310

Subsurface Stress Fields in Single Crystal (Anisotropic) Contacts  

NASA Technical Reports Server (NTRS)

Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and fatigue stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. Techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts are presented in this report. Figure 1 shows typical damper contact locations in a turbine blade. The subsurface stress results are used for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades.

Arakere, Nagaraj K.

2003-01-01

311

Chiral multichromic single crystals for optical devices (LDRD 99406).  

SciTech Connect

This report summarizes our findings during the study of a novel system that yields multi-colored materials as products. This system is quite unusual as it leads to multi-chromic behavior in single crystals, where one would expect that only a single color would exist. We have speculated that these novel solids might play a role in materials applications such as non-linear optics, liquid crystal displays, piezoelectric devices, and other similar applications. The system examined consisted of a main-group alkyl compound (a p block element such as gallium or aluminum) complexed with various organic di-imines. The di-imines had substituents of two types--either alkyl or aromatic groups attached to the nitrogen atoms. We observed that single crystals, characterized by X-ray crystallography, were obtained in most cases. Our research during January-July, 2006, was geared towards understanding the factors leading to the multi-chromic nature of the complexes. The main possibilities put forth initially considered (a) the chiral nature of the main group metal, (b) possible reduction of the metal to a lower-valent, radical state, (c) the nature of the ligand(s) attached to the main group metal, and (d) possible degradation products of the ligand leading to highly-colored products. The work carried out indicates that the most likely explanation considered involves degradation of the aromatic ligands (a combination of (c) and (d)), as the experiments performed can clearly rule out (a) and (b).

Kemp, Richard Alan; Felix, Ana M. (University of New Mexico, Albuquerque, NM)

2006-12-01

312

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

PubMed Central

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

2014-01-01

313

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

314

The cadmium oxide-tungsten oxide phase system and growth of cadmium tungstate single crystals  

Microsoft Academic Search

The results of a further study of the cadmium oxide-tungsten oxide phase diagram are presented and the results of attempts to prepare single crystals of cadmium tungstate. The defects encountered in the crystals and attempts to eliminate them are described and the best conditions for growth of high-quality single crystals detailed. The relationship of the defects to the crystal growth

D. S. Robertson; I. M. Young; J. R. Telfer

1979-01-01

315

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

NASA Astrophysics Data System (ADS)

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; Perumal, Rajesh Narayana

2014-04-01

316

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

317

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

318

Morphological, structural and electrical investigations on non-polar a-plane ZnO epilayers  

Microsoft Academic Search

We report on the growth of non-polar a-plane ZnO by CVD on r-plane-sapphire-wafers, a-plane GaN-templates and a-plane ZnO single-crystal substrates. Only the homoepitaxial growth approach leads to a Frank–van-der–Merwe growth mode, as shown by atomic force microscopy. The X-ray-diffraction spectra of the homoepitaxial thin films mirror the excellent crystalline quality of the ZnO substrate. The morphological and the structural quality

Stefan Lautenschlaeger; Sebastian Eisermann; Michael N. Hofmann; Udo Roemer; Melanie Pinnisch; Andreas Laufer; Bruno K. Meyer; Holger von Wenckstern; Alexander Lajn; Florian Schmidt; Marius Grundmann; Juergen Blaesing; Alois Krost

2010-01-01

319

Magnetism of powder samples and of single crystals  

NASA Astrophysics Data System (ADS)

The temperature dependence of the magnetic order parameter of NiF2, MnCO3 and K2NiF4 measured on powder samples is compared with data obtained on single crystals. It is found that the dynamic dimensionality of the NiF2 and MnCO3 powder samples is one-dimensional (1D) for all temperatures Tsingle crystals isotropic 3D dynamic symmetry is observed. In order to explain isotropy in the bulk single crystals a dynamic averaging process over all domain orientations has to be postulated. For single crystal material of K2NiF4 a critical exponent of ?=0.14±0.01 has been reported. Our neutron diffraction measurements on powder material yield to a very good approximation mean field critical behaviour indicating isotropic dynamics in the critical range. This unexpected result points to a dynamic averaging process over all differently oriented powder grains. As we have argued earlier, the observed universality in the dynamics of ordered magnets is due to a boson guiding field. Averaging over all powder grains, requests that the mean free path of the field bosons is larger than the size of the grains. Additionally, it must be assumed that the field quanta are able to tunnel across the interface between adjacent grains. In polycrystalline bulk samples of the 2D ferromagnet Rb2CrCl4 and of the 1D antiferromagnet KCuF3 also mean field critical behaviour is identified. As a consequence, a similar averaging process as in the K2NiF4 powder sample can be assumed to average over the mosaic structure of polycrystalline bulk material of Rb2CrCl4 and KCuF3. High quality single crystals of Rb2CrCl4 and of KCuF3 exhibit critical exponent of ?~0.3. Dependence of the critical exponents on the mesoscopic morphology of the sample is considered as a typical indication of a boson controlled dynamics, and may partly explain the surprisingly broad distribution of critical exponent values reported in literature.

Köbler, U.; Hoser, A.

2014-01-01

320

Biaxial constitutive modelling and testing of a single crystal superalloy at elevated temperatures  

NASA Technical Reports Server (NTRS)

A viscoplastic constitutive model for single crystal superalloys is developed from crystallographic slip theory. The model is applied to the tension and torsion deformation behavior of the single crystal superalloy PWA 1480 at 871 C (1600 F). Both octahedral and cube slip behavior are needed to model the deformation behavior of single crystal superalloys at elevated temperature.

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

1989-01-01

321

Active Slip Band Separation and the Energetics of Slip in Single Crystals  

E-print Network

Active Slip Band Separation and the Energetics of Slip in Single Crystals to the prediction of stress-strain relations for single crystals and to give precise formulations of experimentally observed connec- tions between hardening of single crystals and separation of active slip

322

Active Slip Band Separation and the Energetics of Slip in Single Crystals  

E-print Network

Active Slip Band Separation and the Energetics of Slip in Single Crystals Luca Deseri David R. Owen­strain relations for single crystals and to give precise formulations of experimentally observed connec­ tions between hardening of single crystals and separation of active slip bands. Non--classical, structured

323

Irradiated cubic single crystal SiC as a high temperature sensor Alex A. Volinsky  

E-print Network

Irradiated cubic single crystal SiC as a high temperature sensor Alex A. Volinsky University to cause point defects formation in different materials. In the case of cubic SiC single crystal radiation was developed a while ago. Single crystal SiC sensor small size (200-500 microns), wide temperature range (150

Volinsky, Alex A.

324

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.

325

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.

326

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

327

MICROSCALE LASER PEEN FORMING OF SINGLE CRYSTAL: DYNAMIC DEFORMATION AND ANISOTROPY  

E-print Network

MICROSCALE LASER PEEN FORMING OF SINGLE CRYSTAL: DYNAMIC DEFORMATION AND ANISOTROPY Yajun Fan and anisotropy in micro-scale laser peen forming of aluminum single crystals have been numerically and provide useful insight into the dynamic shock peen-forming process of single crystal. DYNAMIC MODELING

Yao, Y. Lawrence

328

Self-assembled zno colloidal photonic crystals: Light channels in cracks  

Microsoft Academic Search

Large-area films of colloidal photonic crystals (PCs) were prepared by self-assembly technique. The films contain ordered PC domains separated by cracks. The size of the domains and cracks can be controlled by the drying process. The angular dependence of the stop-band was studied by changing the angle of incidence ? between the beam and the (111) direction, from 0° to

Xie Juan; Deng Hong; Xu Zi-qiang; Li Yan; Huang Jun

2006-01-01

329

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

330

Spectroscopic characterization of YAG and Nd:YAG single crystals  

NASA Astrophysics Data System (ADS)

In this paper, we used the Czochralski method to obtain good quality yttrium aluminium garnet (YAG, Y3Al5O12) and yttrium aluminium garnet doped with neodymium (Nd:YAG) crystals. The investigations were based on the growth mechanisms and the shape of the liquid/solid interface crystallization front on the crystal properties and incorporation of Nd3+ ions. The obtained single YAG and Nd:YAG crystals were studied by use of x-ray diffraction, Raman and IR spectroscopy. There are strong metal oxygen vibrations in the region of 650–800 cm?1 which are characteristics of Al-O bond: peaks at 784/854, 719/763 and 691/707 cm?1 correspond to asymmetric stretching vibrations in tetrahedral arrangement. Peaks at 566/582, 510/547 and 477/505 cm?1 are asymmetric stretching vibrations and 453/483 cm?1 is the symmetric vibration of the Al-O bond in octahedral arrangements of the garnet structure. Lower energy peaks correspond to translation and vibration of cations in different coordinations—tetrahedral, octahedral and dodecahedral in the case of the lowest modes.

Kosti?, S.; Lazarevi?, Z.; Rom?evi?, M.; Radojevi?, V.; Milutinovi?, A.; Staniši?, G.; Gili?, M.

2014-09-01

331

ESR Study on Irradiated Ascorbic Acid Single Crystal  

SciTech Connect

Food irradiation is a 'cold' process for preserving food and has been established as a safe and effective method of food processing and preservation after more than five decades of research and development. The small temperature increase, absence of residue and effectiveness of treatment of pre-packed food are the main advantages. In food industry, ascorbic acid and its derivatives are frequently used as antioxidant agents. However, irradiation is expected to produces changes in the molecules of food components and of course in the molecules of the agents added as preservation agents such as ascorbic acid. These changes in the molecular structures could cause decreases in the antioxidant actions of these agents. Therefore, the radiation resistance of these agents must be known to determine the amount of radiation dose to be delivered. Electron spin resonance (ESR) is one of the leading methods for identification of intermediates produced after irradiation. ESR spectrum of irradiated solid powder of ascorbic acid is fairly complex and determinations of involved radical species are difficult. In the present work, single crystals of ascorbic acid irradiated by gamma radiation are used to determine molecular structures of radiation induced radicalic species and four radicalic species related in pair with P21 crystal symmetry are found to be responsible from experimental ESR spectrum of gamma irradiated single crystal of ascorbic acid.

Tuner, H.; Korkmaz, M. [Hacettepe University, Department of Physics Engineering, Ankara, 06800 (Turkey)

2007-04-23

332

Lithium containing chalcogenide single crystals for neutron detection  

NASA Astrophysics Data System (ADS)

Lithium containing semiconductor-grade chalcogenide single crystals were grown using the vertical Bridgman method. The source material was synthesized from elementary precursors in two steps, (i) preparing the metal alloy LiIn or LiGa, and (ii) reaction with chalcogen - Se or Te. In a number of experiments, enriched 6Li isotope was used for synthesis and growth. The composition and structure of the synthesized materials was verified using powder X-Ray diffraction. The energy band gaps of the crystals were determined using optical absorption measurements. The resistivity of LiInSe2 and LiGaSe2, obtained using current-voltage measurements is on the order of 108-1011 ? cm. Photoconductivity measurement of a yellow LiInSe2 sample showed a peak in the photocurrent around 445 nm. Nuclear radiation detectors were fabricated from single crystal wafers and the responses to alpha particles, neutrons and gammas were measured and presented. It suggests that this material is a promising candidate for neutron detection applications.

Tupitsyn, E.; Bhattacharya, P.; Rowe, E.; Matei, L.; Cui, Y.; Buliga, V.; Groza, M.; Wiggins, B.; Burger, A.; Stowe, A.

2014-05-01

333

Strain incompatibility and residual strains in ferroelectric single crystals.  

PubMed

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 BaTiO(3) 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

334

Plastic deformation of Ni{sub 3}Nb single crystals  

SciTech Connect

Temperature dependence of yield stress and operative slip system in Ni{sub 3}Nb single crystals with the D0{sub a} structure was investigated in comparison with that in an analogous L1{sub 2} structure. Compression tests were performed at temperatures between 20 C and 1,200 C for specimens with loading axes perpendicular to (110), (331) and (270). (010)[100] slip was operative for three orientations, while (010)[001] slip for (331) and {l{underscore}brace}211{r{underscore}brace}{lt}{bar 1}{bar 0} 7 13{gt} twin for (270) orientations were observed, depending on deformation temperature. The critical resolved shear stress (CRSS) for the (010)[100] slip anomaly increased with increasing temperature showing a maximum peak between 400 C and 800 C depending on crystal orientation. The CRSS showed orientation dependence and no significant strain rate dependence in the temperature range for anomalous strengthening. The [100] dislocations with a screw character were aligned on the straight when the anomalous strengthening occurred. The anomalous strengthening mechanism for (010)[100] slip in Ni{sub 3}Nb single crystals is discussed on the basis of a cross slip model which has been widely accepted for some L1{sub 2}-type compounds.

Hagihara, Kouji; Nakano, Takayoshi; Umakoshi, Yukichi

1999-07-01

335

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

336

Role of grain boundaries in ZnO  

NASA Astrophysics Data System (ADS)

ZnO is used in a wide variety of applications owing to the electrical properties. Polycrystalline ZnO ceramics have long been used such as varistor, and ZnO films are currently intensively studied for transparent conductor applications. Grain boundary (GB) in ZnO varistor is believed to be the origin of nonlinear current-voltage characteristics, and GB in ZnO films possibly affects the electrical conductivity. It is therefore important to understand the role of ZnO GB on the electrical properties, which should be closely related with the structure in atomic scale. With these viewpoints, we have studied the atomistic structure of ZnO GBs, where the orientation relations of adjacent crystals are well defined. Single GBs studied were obtained by fabricating ZnO bicrystals and the GBs were characterized by scanning transmission electron microscopy (STEM) and theoretical calculations. It is found that coordination number of ions change in ZnO GBs; there are underfold or overfold coordinated ions that are unusual in bulk inside. It is calculated that these atomistic structures alters the electronic structure but would not create deep states in the band gap. On the other hand, when praseodymium (Pr), which is known to be a key dopant element to obtain nonlinear (I-V) characteristics, is added to the GBs, Pr strongly localizes to the GBs and occupies specific atomic sites. Pr facilitates the formation of the acceptorlike defects such as zinc vacancies, which we think that is an important role of Pr on generation of nonlinear (I-V) characteristics. Furthermore, atomic arrangement and localization behavior of Pr are studied for several GBs to obtain fundamental understanding about GB structure formation.

Sato, Yukio; Ikuhara, Yuichi

2014-03-01

337

Ohmic-rectifying conversion of Ni contacts on ZnO and the possible determination of ZnO thin film surface polarity.  

PubMed

The current-voltage characteristics of Ni contacts with the surfaces of ZnO thin films as well as single crystal (0001) ZnO substrate are investigated. The ZnO thin film shows a conversion from Ohmic to rectifying behavior when annealed at 800°C. Similar findings are also found on the Zn-polar surface of (0001) ZnO. The O-polar surface, however, only shows Ohmic behavior before and after annealing. The rectifying behavior observed on the Zn-polar and ZnO thin film surfaces is associated with the formation of nickel zinc oxide (Ni1-xZnxO, where x?=?0.1, 0.2). The current-voltage characteristics suggest that a p-n junction is formed by Ni1-xZnxO (which is believed to be p-type) and ZnO (which is intrinsically n-type). The rectifying behavior for the ZnO thin film as a result of annealing suggests that its surface is Zn-terminated. Current-voltage measurements could possibly be used to determine the surface polarity of ZnO thin films. PMID:24466144

Saw, Kim Guan; Tneh, Sau Siong; Tan, Gaik Leng; Yam, Fong Kwong; Ng, Sha Shiong; Hassan, Zainuriah

2014-01-01

338

Ohmic-Rectifying Conversion of Ni Contacts on ZnO and the Possible Determination of ZnO Thin Film Surface Polarity  

PubMed Central

The current-voltage characteristics of Ni contacts with the surfaces of ZnO thin films as well as single crystal (0001) ZnO substrate are investigated. The ZnO thin film shows a conversion from Ohmic to rectifying behavior when annealed at 800°C. Similar findings are also found on the Zn-polar surface of (0001) ZnO. The O-polar surface, however, only shows Ohmic behavior before and after annealing. The rectifying behavior observed on the Zn-polar and ZnO thin film surfaces is associated with the formation of nickel zinc oxide (Ni1-xZnxO, where x?=?0.1, 0.2). The current-voltage characteristics suggest that a p-n junction is formed by Ni1-xZnxO (which is believed to be p-type) and ZnO (which is intrinsically n-type). The rectifying behavior for the ZnO thin film as a result of annealing suggests that its surface is Zn-terminated. Current-voltage measurements could possibly be used to determine the surface polarity of ZnO thin films. PMID:24466144

Saw, Kim Guan; Tneh, Sau Siong; Tan, Gaik Leng; Yam, Fong Kwong; Ng, Sha Shiong; Hassan, Zainuriah

2014-01-01

339

Metastable X centers in cadmium telluride single crystals  

NASA Astrophysics Data System (ADS)

A model is proposed for metastable DX centers formed through Jahn-Teller distortion of the crystal lattice of cadmium telluride, i.e., through the displacement of a D Cd residual donor impurity atom (where D is a Group III element of the periodic table) to the region of a nearest neighbor interstice. The configuration-coor-dinate diagram for a V Cd- D i associated defect is constructed with due regard for the tetrahedral and hexagonal positions of interstitial atoms. The Stokes shift, n-type conductivity, location of the Fermi level, specific features of photoluminescence, and some other effects are explained in terms of the configuration-coordinate diagram. The results of experimental investigations of the energy spectrum of DX centers in cadmium telluride single crystals are in agreement with available theoretical data.

Tkachuk, P. N.; Tkachuk, V. I.; Bukivsky, P. N.; Kurik, M. V.

2004-05-01

340

Display projector technology by way of single crystal faceplate technology  

NASA Astrophysics Data System (ADS)

Three single crystal faceplates were to be integrated into Cathode Ray Tube (CRT) envelopes with the intent of evaluating the light output from Ce:YAG (Green), modified Ce:GD, YAG (Orange), and CE:BEL (Blue). These CRT's were to be mounted in the projection test bed developed under Contract N61339-90-C-0047 and furnished G.F.P. to Trident International, Inc. for use and delivery during this contract. Three 3 inch diameter Ce:YAG faceplates were supplied as G.F.P. from the previous contract N61339-90-C-0047. One of these three was to be used for construction of a CRT, the remaining two were to be used for the coating test. During the processing of the CRT's, one of the crystals was destroyed. The other two single crystal faceplates were incorporated in test CRT's. An additional Ce:Gd, YAG (Red shifted green) faceplate of 1.5 inches diameter and two Ce:BEL (Blue) crystals of 0.75 inch diameter were obtained from Allied Signal, Inc, by Trident. Investigations were made to provide optimum optical coupling of the CRT light output into a projection lens. Index matching heat dissipation fluids were used. A wide angle lens was selected and supplied by the contractor. Filtering of the light output of the Ce:YAG, Ce:Gd, YAG and Ce:BEL faceplates was investigated for use in producing green, red, and blue light outputs suitable for a full color video projector.

Tucker, A.; Kindl, H. J.

1993-09-01

341

Field emission properties of single crystal chromium disilicide nanowires  

SciTech Connect

The composition, crystal structure, and field emission properties of high-crystallinity chromium disilicide (CrSi{sub 2}) 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 CrSi{sub 2} nanowires. Field emission measurements show that an emission current density of 0.1 {mu}A/cm{sup 2} was obtained at a turn-on electric field intensity of 2.80 V/{mu}m. The maximum emission current measured was 1.86 mA/cm{sup 2} at 3.6 V/{mu}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 CrSi{sub 2}. The thermal tolerance of the nanowires was studied up to a temperature of 1100 Degree-Sign C. The stability of the field emission current, the I-E values, their thermal tolerance, and high electrical conductivity make CrSi{sub 2} nanowires a promising material for field emission applications.

Valentin, L. A.; Carpena-Nunez, J.; Yang, D.; Fonseca, L. F. [Department of Physics, University of Puerto Rico, Rio Piedras Campus, P.O. Box 70377, San Juan, 00931 (Puerto Rico)

2013-01-07

342

Thermal neutron dosimeter by synthetic single crystal diamond devices.  

PubMed

We report on a new solid state dosimeter based on chemical vapor deposition (CVD) single crystal diamond fabricated at Roma "Tor Vergata" University laboratories. The dosimeter has been specifically designed for direct neutron dose measurements in boron neutron capture therapy (BNCT). The response to thermal neutrons of the proposed diamond dosimeter is directly due to (10)B and, therefore, the dosimeter response is directly proportional to the boron absorbed doses in BNCT. Two single crystal diamond detectors are fabricated in a p-type/intrinsic/metal configuration and are sandwiched together with a boron containing layer in between the metallic contacts (see Fig.1). Neutron irradiations were performed at the Frascati Neutron Generator (FNG) using the 2.5 MeV neutrons produced through the D(d,n)(3)He fusion reaction. Thermal neutrons were then produced by slowing down the 2.5 MeV neutrons using a cylindrical polymethylmethacrylate (PMMA) moderator. The diamond dosimeter was placed in the center of the moderator. The products of (10)B(n,alpha)Li nuclear reaction were collected simultaneously giving rise to a single peak. Stable performance, high reproducibility, high efficiency and good linearity were observed. PMID:19375336

Almaviva, S; Marinelli, Marco; Milani, E; Prestopino, G; Tucciarone, A; Verona, C; Verona-Rinati, G; Angelone, M; Pillon, M

2009-07-01

343

Isomeric ionic lithium isonicotinate three-dimensional networks and single-crystal-to-single-crystal rearrangements generating microporous materials.  

PubMed

Reaction between LiOH and isonicotinic acid (inicH) in the appropriate solvent or mixture of solvents affords a family of variously solvated forms of a simple ionic lithium salt, viz., Li(+)inic(-)·S (where S = 0.5 morpholine, 0.5 dioxane, 0.25 n-hexanol, 0.5 N-methylpyrrolidinone, 0.5 N,N-dimethylformamide, 0.5 n-propanol, 0.5 cyclohexanol, 0.5 pyridine, 0.5 t-butanol, 0.5 ethanol, and 0.5 methanol). Three-dimensional Li(+)inic(-) frameworks containing solvent-filled channels are present in all of these except for the MeOH and EtOH solvates. The nondirectional character of the electrostatic interactions between the Li(+) and inic(-) ions bestows an element of "plasticity" upon the framework, manifested in the observation of no less than five different framework structures within the family. Unusual single-crystal-to-single-crystal transformations accompany desolvation of Li(+)inic(-)·S in which the Li(+)inic(-) framework undergoes a major rearrangement (from a structure containing "8484 chains" to one with "6666 chains"). The "before and after" structures are strongly suggestive of the mechanism and the driving force for these solid state framework rearrangements: processes which further demonstrate the "plasticity" of the ionic Li(inic) framework. A solid-state mechanism for these desolvation processes that accounts very satisfactorily for the formation of the channels and for the diverse geometrical/topological aspects of the transformation is proposed. The reverse process allows the regeneration of the solvated 8484 form. When the 6666 Li(+)inic(-) form is immersed in carbon disulfide, a single-crystal-to-single-crystal transformation occurs to generate Li(+)inic(-)·0.25CS2. The hydrate, Li(+)inic(-)·2H2O which consists of discrete Li(inic)·H2O chains obtained by recrystallizing the salt from water, can also be obtained by hydration of the 6666 form. A dense 3D network with the formula, Li(inic) can be obtained in a reversible process by the removal of the water from the hydrated form and also by crystallization from a t-amyl alcohol solution. PMID:24811943

Abrahams, Brendan F; Dharma, A David; Grannas, Martin J; Hudson, Timothy A; Maynard-Casely, Helen E; Oliver, Graham R; Robson, Richard; White, Keith F

2014-05-19

344

Advanced piezoelectric single crystal based transducers for naval sonar applications  

NASA Astrophysics Data System (ADS)

TRS is developing new transducers based on single crystal piezoelectric materials such as Pb(Mg1/3Nb2/3)x-1TixO3 (PMN-PT). Single crystal piezoelectrics such as PMN-PT exhibit very high piezoelectric coefficients (d33 ~ 1800 to >2000 pC/N) and electromechanical coupling factors (k33 > 0.9), respectively, which may be exploited for improving the performance of broad bandwidth and high frequency sonar. Apart from basic performance, much research has been done on reducing the size and increasing the output power of tonpilz transducers for sonar applications. Results are presented from two different studies. "33" mode single crystal tonpilz transducers have reduced stack lengths due to their low elastic stiffness relative to PZTs, however, this produces non-ideal aspect ratios due to large lateral dimensions. Alternative "31" resonance mode tonpilz elements are proposed to improve performance over these "33" designs. d32 values as high as 1600 pC/N have been observed, and since prestress is applied perpendicular to the poling direction, "31" mode Tonpilz elements exhibit lower loss and higher reliability than "33" mode designs. Planar high power tonpilz arrays are the optimum way to obtain the required acoustic pressure and bandwidth for small footprint, high power sensors. An important issue for these sensors is temperature and prestress stability, since fluctuations in tonpilz properties affects power delivery and sensing electronic design. TRS used the approach of modifying the composition of PMN-PT to improve the temperature dependence of properties of the material. Results show up to a 50% decrease in temperature change while losing minimal source level.

Snook, Kevin A.; Rehrig, Paul W.; Hackenberger, Wesley S.; Jiang, Xiaoning; Meyer, Richard J., Jr.; Markley, Douglas

2005-05-01

345

Ion-beam-produced structural defects in ZnO  

Microsoft Academic Search

We study the evolution of lattice defects in single-crystal ZnO bombarded with 60-keV 28Si and 300-keV 197Au ions at 77 and 300 K. To characterize ion-beam-produced structural defects, we use a combination of Rutherford backscattering\\/channeling (RBS\\/C) spectrometry, cross-sectional transmission electron microscopy (XTEM), x-ray photoelectron spectroscopy, and atomic force microscopy. Results show that ZnO exhibits strong dynamic annealing, and even high-dose

S. O. Kucheyev; J. S. Williams; C. Jagadish; J. Zou; Cheryl Evans; A. J. Nelson; A. V. Hamza

2003-01-01

346

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

347

Dielectric response and magnetoelectric coupling in single crystal gallium ferrite  

NASA Astrophysics Data System (ADS)

Here we report the dielectric response and electric conduction behavior of magnetoelectric gallium ferrite single crystals studied using impedance analysis in time and temperature domain. The material exhibits two distinct relaxation processes: a high frequency bulk response and a low frequency interfacial boundary layer response. Calculated bulk capacitance as a function of temperature showed an anomaly at ferri- to paramagnetic transition temperature (˜ 300 K), suggestive of magneto-dielectric coupling in the material. Interestingly, we also witness an abrupt change in the activation energy at ˜ 220 K, in the vicinity of spin-glass transition temperature in GaFeO3.

Mukherjee, Somdutta; Gupta, Rajeev; Garg, Ashish

2013-05-01

348

High temperature hardness of bulk single crystal GaN  

SciTech Connect

The hardness of single crystal GaN (gallium nitride) at elevated temperature is measured for the first time and compared with other materials. A Vickers indentation method was used to determine the hardness of crack-free GaN samples under an applied load of 0.5 N in the temperature range 20--1,200 C. The hardness is 10.8 GPa at room temperature, which is comparable to that of Si. At elevated temperatures GaN shows higher hardness than Si and GaAs. A high mechanical stability for GaN at high temperature is deduced.

Yonenaga, I.; Hoshi, T.; Usui, A.

2000-07-01

349

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

350

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

351

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

Tauber, Daniela; von Borczyskowski, Christian

2013-01-01

352

The sublimation kinetics of GeSe single crystals  

NASA Technical Reports Server (NTRS)

The sublimation kinetics of (001) oriented GeSe single crystal platelets was studied by high-temperature mass spectroscopy, quantitative vacuum microbalance techniques, and hot stage optical microscopy. For a mean experimental temperature of 563 K, the activation enthalpy and entropy are found to equal 32.3 kcal/mole and 19.1 eu, respectively. The vaporization coefficient is less than unity for the range of test temperatures, and decreases with increasing temperature. The combined experimental data are correlated by means of a multistep surface adsorption mechanism.

Irene, E. A.; Wiedemeier, H.

1975-01-01

353

Single-crystal indicators of fatigue and plastic deformation damage  

NASA Astrophysics Data System (ADS)

Specially prepared thin single-crystal plates rigidly fastened to the sample surface area are shown to be effective as sensor elements (indicators and detectors) of the deformation damage of multi-phase commercial alloys under fatigue and static loading. It is proposed to estimate the lifetime and the strain of basic material by monitoring the geometric characteristics of band patterns on the detector surface. It is shown that density, direction of deformation bands and fractal dimension of band patterns on surfaces of indicators correlate with the number of cycles, maximum applied stress (fatigue loading) and plastic strain, temperature (static loading).

Gordienko, Y. G.; Zasimchuk, E. E.

1994-09-01

354

Cryogenic Scanning Tunneling Spectroscopy of Superconducting Iron Chalcogenide Single Crystals  

NASA Astrophysics Data System (ADS)

We report scanning tunneling spectroscopy measurements on the iron-based superconductors of the "11" family including Fe1-yTe1-xSex and Fe1-yTe1-xSx. Conductance spectra and atomically-resolved images are obtained on single crystals down to 300 mK. A gap-like structure is observed, showing an asymmetric spectral background, non-trivial spatial variation and temperature dependence. We discuss our data in terms of possible gap anisotropy and doping inhomogeneities, and in relation to other recent spectroscopic measurements on iron-based superconductors.

Wei, J. Y. T.; Fridman, Igor; Yeh, Kuo-Wei; Wu, Maw-Kuen; Hu, Rongwei; Petrovic, C.

2011-03-01

355

Optical properties of Ce:Mn:KLN single crystals  

NASA Astrophysics Data System (ADS)

CeO2 and MnCO3 codoped Potassium Lithium Niobate single crystals were grown by the Czochralski method. It was shown that Ce ions would be precedently substituted for the site of K by the absorption spectra and X-ray diffraction patterns. Otherwise Mn would be substitute for the site of Nb. The response time, exponential gain coefficient and effective carries density was measured by the two beam coupling. The effect of Oxide and reduced treatment on these parameters was researched.

Yang, Chunhui; Chen, Gang; Wang, Biao

2001-10-01

356

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

357

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

358

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

359

Preparation of Black Phosphorus Single Crystals by a Completely Closed Bismuth-Flux Method and Their Crystal Morphology  

Microsoft Academic Search

Needle-shaped and film- or plate-shaped black phosphorus single crystals were prepared by an improved bismuth-flux method. The conversion of red phosphorus to white phosphorus and the growth of black phosphorus single crystals from the solution of white phosphorus in liquid bismuth were performed in an evacuated quartz-glass apparatus without breaking the vacuum. Needle crystals measured about 5 mm in length

Mamoru Baba; Fukunori Izumida; Yuji Takeda; Akira Morita

1989-01-01

360

Electronic Properties of CuxTiSe2 Single Crystals  

NASA Astrophysics Data System (ADS)

We investigate the normal state and superconducting properties of 1T-TiSe2 family of single crystals intercalated with different level of copper content. Magnetoresistance and Hall effect data indicate that 1T-TiSe2 is a compensated narrow band-gap semiconductor or semimetal with small number of electron and hole carriers. We compare the influence of copper intercalant and titanium interstiatials on the temperature evolution of charge density waves via resistivity and Hall effect measurements. Our findings indicate that the origin of the charge density waves in 1T-TiSe2 is due to the combination of exciton and Jahn-Teller mechanisms. At higher copper concentrations we investigate the superconducting properties of CuxTiSe2 in overdoped regime and find that the system is a single-gap strongly type-II superconductor with in-plane Ginzburg-Landau parameter reaching 50.

Husanikova, Petra; Fedor, Jan; Derer, Jan; Cambel, Vladimir; Karapetrov, Goran

2013-03-01

361

Ferromagnetism in Single Crystal MoS2  

NASA Astrophysics Data System (ADS)

We report on the magnetic properties of MoS2 flakes measured from room temperature down to 10 K and magnetic fields up to 5 Tesla. Molybdenum disulfide (MoS2) is one of the most stable layered transition metal dichalcogenides, which has a finite band gap and is regarded as a complementary (quasi-) 2D material to graphene. We find that single crystals of MoS2 display ferromagnetism superimposed onto a large temperature-dependent diamagnetism and observe that ferromagnetism persists from 10 K up to room temperature. We attribute the existence of ferromagnetism partly to the presence of zigzag edges in the magnetic ground state at the grain boundaries. Since the magnetic measurements are relatively insensitive to the interlayer coupling, these results are expected to be also valid in the single layer limit.

Saeidi Varnoosfaderani, Sima; Tongay, Sefaattin; Appleton, Bill; Wu, Junqiao; Hebard, Arthur

2013-03-01

362

Axially dependent dielectric relaxation response of natural hydroxyapatite single crystals  

NASA Astrophysics Data System (ADS)

A thermally stimulated depolarization current (TSDC) study of single crystals of natural fluorine-rich hydroxyapatite, polarized with the electric field (Ep) applied parallel and perpendicular to the c axis, has revealed relaxation modes with axially dependent dielectric behavior. The (re)orientation of the OH- ions in the columns and the hydroxyls of the structural H2O molecules give rise to two prominent thermocurrent bands in the temperature range of approx200-340 K. Several weak current bands, below approx200 K, are related to the relaxation of impurity-Ca2+ vacancy (I-V) dipoles. The I-V mechanisms are particularly effective in the case where Epperpendicularc axis and are considered to take place via cation jumps on planes perpendicular to the 0001 crystal axis, at regions near "distorted" Ca(II) triangles (i.e., triangles which include impurity ions and Ca2+ vacancies). The band attributed to rotational relaxation of the OH- ions in the columns shows particular strength when Epperpendicularc axis, and an extensive distribution of relaxation times. The distribution is due to the multiplicity of physicochemical interactions between the OH- ions and their ionic and molecular neighbors (hydrogen bonds with adjacent F-, Cl-, and O2- ions, varying steric hindrances, etc.). The changes induced in the TSDC spectra after annealing processes at selected high temperatures are interpreted based on the gradual loss of structural H2O molecules located in oxygen or calcium vacancies and the resulting local changes in the crystal lattice.

Kalogeras, Ioannis M.; Vassilikou-Dova, Aglaia; Katerinopoulou, Anna

2002-07-01

363

Pockels effect in yttrium aluminum borate single crystals  

NASA Astrophysics Data System (ADS)

Experimental measurements of linear electro-optical coefficients are reported for YAl3(BO3)4 (YAB) single crystals for the two principal tensor components xyz and yyy at the wavelength of a CW semiconducting GaAlAs laser emitting at 1040 nm. We have found the values of the Pockels coefficients to be equal to 0.21 ± 0.06 and 0.56 ± 0.08 pm/V for 123 and 222 Pockels components, respectively. Additional measurements performed for the thin-cut samples with the thickness varying within the 100 500 ?m have confirmed the values of the corresponding parameters. We have eliminated a contribution of the piezooptical coefficients as well as for other disturbing factors. We have established that the crystals with a different number of defects do not show any differences, which indicate the principal role of the borate clusters on the observed effects. The temperature changes are very low (due to a low ionic contribution), and do not exceed 5 6%, which indicates the low contribution of the electron-phonon to the Pockels effect. Because the YAB crystals possess a very large photothermal damage (more than 15 GW/cm2) and are only slightly temperature dependent. Hence, they may be proposed as promising materials for high-power laser electro-optic modulators.

Reshak, A. H.; Majchrowski, A.; Imiolek, W.

2008-10-01

364

ZnO nanorods for electronic and photonic device applications  

NASA Astrophysics Data System (ADS)

We report on catalyst-free growth of ZnO nanorods and their nano-scale electrical and optical device applications. Catalyst-free metalorganic vapor-phase epitaxy (MOVPE) enables fabrication of size-controlled high purity ZnO single crystal nanorods. Various high quality nanorod heterostructures and quantum structures based on ZnO nanorods were also prepared using the MOVPE method and characterized using scanning electron microscopy, transmission electron microscopy, and optical spectroscopy. From the photoluminescence spectra of ZnO/Zn 0.8Mg 0.2O nanorod multi-quantum-well structures, in particular, we observed a systematic blue-shift in their PL peak position due to quantum confinement effect of carriers in nanorod quantum structures. For ZnO/ZnMgO coaxial nanorod heterostructures, photoluminescence intensity was significantly increased presumably due to surface passivation and carrier confinement. In addition to the growth and characterizations of ZnO nanorods and their quantum structures, we fabricated nanoscale electronic devices based on ZnO nanorods. We report on fabrication and device characteristics of metal-oxidesemiconductor field effect transistors (MOSFETs), Schottky diodes, and metal-semiconductor field effect transistors (MESFETs) as examples of the nanodevices. In addition, electroluminescent devices were fabricated using vertically aligned ZnO nanorods grown p-type GaN substrates, exhibiting strong visible electroluminescence.

Yi, Gyu-Chul; Yoo, Jinkyoung; Park, Won Il; Jung, Sug Woo; An, Sung Jin; Kim, H. J.; Kim, D. W.

2005-11-01

365

Microstructural modeling of recrystallization in deformed iron single crystals  

NASA Astrophysics Data System (ADS)

Recrystallization kinetics in a (111)[1bar 10] iron single crystal deformed 70 pet by rolling were characterized experimentally at temperatures between 500°C and 600°C by means of quantitative metallography. A Laplace transform method was applied to the time-dependent global microstructural properties, volume fraction, interface area per unit volume, and the largest intercept-free length (recrystallized grain) to separate nucleation and interface migration effects from the overall recrystallization kinetics. A comprehensive nucleation and growth model was derived from analysis of the microstructural data. The model consisted of the following salient features: (a) nucleation was random and approximately site-saturated with zero incubation time at all temperatures; (b) the recrystallized grains grew three-dimensionally in the shape of prolate spheroids; and (c) interface migration rates were highly anisotropic, the grains growing at an approximately constant rate in one dimension and at a strongly decreasing rate in the other two dimensions. The present findings were compared to a similar earlier study of a deformed iron (111)[bar 1 bar 12] single crystal. The time dependencies of the interface migration rates were rationalized in terms of a deformation-induced, nonuniform distribution of stored energy and an orientation-dependent grain boundary mobility.

Vandermeer, R. A.; Rath, B. B.

1989-10-01

366

Single crystal diamond detectors grown by chemical vapor deposition  

NASA Astrophysics Data System (ADS)

The detection properties of heteropitaxial (polycrystalline, pCVD) and homoepitaxial (single crystal, scCVD) diamond films grown by microwave chemical vapor deposition (CVD) in the Laboratories of Roma "Tor Vergata" University are reported. The pCVD diamond detectors were tested with ?-particles from different sources and 12C ions produced by 15 MV Tandem accelerator at Southern National Laboratories (LNS) in Catania (Italy). pCVDs were also used to monitor 14 MeV neutrons produced by the D-T plasma at Joint European Torus (JET), Culham, U.K. The limit of pCVDs is the poor energy resolution. To overcome this problem, we developed scCVD diamonds using the same reactor parameters that optimized pCVD diamonds. scCVD were grown on a low cost (1 0 0) HPHT single crystal substrate. A detector 110 ?m thick was tested under ?-particles and under 14 MeV neutron irradiation. The charge collection efficiency spectrum measured under irradiation with a triple ?-particle source shows three clearly resolved peaks, with an energy resolution of about 1.1%. The measured spectra under neutron irradiation show a well separated C(n,?0)9Be12 reaction peak with an energy spread of 0.5 MeV for 14.8 MeV neutrons and 0.3 MeV for 14.1 MeV neutrons, which are fully compatible with the energy spread of the incident neutron beams.

Tuvè, C.; Angelone, M.; Bellini, V.; Balducci, A.; Donato, M. G.; Faggio, G.; Marinelli, M.; Messina, G.; Milani, E.; Morgada, M. E.; Pillon, M.; Potenza, R.; Pucella, G.; Russo, G.; Santangelo, S.; Scoccia, M.; Sutera, C.; Tucciarone, A.; Verona-Rinati, G.

2007-01-01

367

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

368

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

369

The fatigue damage behavior of a single crystal superalloy  

NASA Technical Reports Server (NTRS)

The uniaxial fatigue behavior of a single crystal superalloy, PWA 1480, is described. Both monotonic tensile and constant amplitude fatigue tests were conducted at room temperature, in an effort to assess the applicability of polycrystalline-based fatigue life prediction methods to a single crystal superalloy. The observed constant amplitude behavior correlated best using a stress-based life criterion. Nearly all specimens failed at surface or slightly subsurface microporosity; this is thought to be responsible for the unusually large amount of scatter in the test results. An additional term is developed in the stress-life equation for the purpose of accounting for the effect of microporosity on fatigue life. The form chosen is a function of the effective area of the failure-producing microporosity projected on a plane perpendicular to the loading axis, as well as the applied stress. This additional term correlated the data to within factors of two on life. Although speculative, extrapolation of the microporosity relation to zero micropore area indicates that approximately an order of magnitude improvement in fatigue life should result.

Mcgaw, Michael A.

1988-01-01

370

Photoelectrical properties of TlGaSe2 single crystals  

NASA Astrophysics Data System (ADS)

The spectral distribution of photocurrent (PC) of TlGaSe2 single crystals in the range of wavelengths between 500 nm and 700 nm possesses a single maximum at 2.04 eV corresponds to the direct energy band gap of this crystal. The PC is enhanced dramatically by pre-illuminations at low temperatures with band gap light. The temperature dependence of PC of the sample investigated in the temperature range from 80 K to 300 K at constant heating rate shows that the overlapping peaks in the PC spectrum are direct reflection of the Thermally Stimulated Current (TSC) associated with the several trapping levels. The PC response is strongly dependent on the degree of occupancy of traps. The wavelength at the maximum of the PC spectrum is found to be dependent on the wavelength scan direction being up or down. The ferroelectric phase transitions of TlGaSe2 are detected at ˜108 K and ˜118 K in the PC spectrum.

Ozdemir, Selahattin; Bucurgat, Mahmut

2014-07-01

371

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

372

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

373

Strong luminescence and efficient energy transfer in Eu3+/Tb3+-codoped ZnO nanocrystals  

NASA Astrophysics Data System (ADS)

Single crystalline Eu3+/Tb3+-codoped ZnO nanocrystals have been synthesized by using a simple co-precipitation method. Successful doping is realized so that strong green and red luminescence can be efficiently excited by ultraviolet and near ultraviolet radiation, demonstrating an efficient energy transfer from ZnO host to rare earth ions. The energy transfer from the ZnO host to Tb3+ in ZnO: Tb3+ samples and ZnO host to Eu3+ in the ZnO: Eu3+ samples under UV excitation are investigated. It is found that the red 5D0 ? 7F2 emission of Eu3+ ions decreases with increasing temperature but the green 5D4 ? 7F5 emission of Tb3+ ions increases with increasing temperature, implying a different energy transfer processes in the two samples. Moreover, energy transfer from Tb3+ ions to Eu3+ ions in ZnO nanocrystals is also observed by analyzing luminescence spectra and the decay curves. By adjusting the doping concentration, the Eu3+/Tb3+-codoped ZnO phosphors emit green and red luminescence with chromaticity coordinates near white light region, high color purity and high intensity, indicating that they are promising light-conversion materials and have potential in field emission display devices and liquid crystal display backlights.

Luo, L.; Huang, F. Y.; Dong, G. S.; Fan, H. H.; Li, K. F.; Cheah, K. W.; Chen, J.

2014-11-01

374

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

375

Anisotropy of magnetic susceptibility in natural olivine single crystals  

NASA Astrophysics Data System (ADS)

flow dynamics can cause preferential alignment of olivine crystals that results in anisotropy of physical properties. To interpret anisotropy in mantle rocks, it is necessary to understand the anisotropy of olivine single crystals. We determined anisotropy of magnetic susceptibility (AMS) for natural olivine crystals. High-field AMS allows for the isolation of the anisotropy due to olivine alone. The orientations of the principal susceptibility axes are related to the olivine's crystallographic structure as soon as it contains >3 wt % FeO. The maximum susceptibility is parallel to the c axis both at room temperature (RT) and at 77 K. The orientation of the minimum axis at RT depends on iron content; it is generally parallel to the a axis in crystals with 3-5 wt % FeO, and along b in samples with 6-10 wt % FeO. The AMS ellipsoid is prolate and the standard deviatoric susceptibility, k', is on the order of 8*10-10 m3/kg for the samples with <1wt % FeO, and ranges from 3.1*10-9 m3/kg to 5.7*10-9 m3/kg for samples with 3-10 wt % FeO. At 77 K, the minimum susceptibility is along b, independent of iron content. The shape of the AMS ellipsoid is prolate for samples with <5 wt % FeO, but can be prolate or oblate for higher iron content. The degree of anisotropy increases at 77 K with p'77 = 7.1 ± 0.5. The results from this study will allow AMS fabrics to be used as a proxy for olivine texture in ultramafic rocks with high olivine content.

Biedermann, Andrea R.; Pettke, Thomas; Reusser, Eric; Hirt, Ann M.

2014-07-01

376

Growth of High Quality A N Single Crystals and Their Optical Properties  

E-print Network

Growth of High Quality A N Single Crystals and Their Optical Properties M. strassburgl, J a two-step growth process in a TaN crucible. Crystal defects and the effect of incorporated impurities,2,3]. Hence, the growth and crystal quality opiimhtion of buk AiN crystals is of primary importance

Nabben, Reinhard

377

Growth of Large Single Crystals of Black Phosphorus under High Pressure  

Microsoft Academic Search

A large volume high pressure apparatus has made it possible to grow large single crystals of black phosphorus, P. After converting red P powder into black P under a high pressure of 10 kbar at high temperature, a melt of polycrystalline black P has been gradually solidified to bring about the growth of single crystals. Crystal sizes larger than 5×

Shoichi Endo; Yuichi Akahama; Shin-ichi Terada; Shin-ichiro Narita

1982-01-01

378

Eect of temperature on superdislocation dissociation in CuZnAl 18R single crystals  

E-print Network

Eect of temperature on superdislocation dissociation in Cu±Zn±Al 18R single crystals A. Cunibertia crystals deformed at temperature above room temper- ature is studied by transmission electron microscopy temperature, an eect commonly observed in several LRO intermetallic compounds. 18R single crystals also

Niewczas, Marek

379

250 W single-crystal fiber Yb:YAG laser Xavier Dlen,1,  

E-print Network

-crystal fiber oscillator pumped at 600 W with a fiber coupled laser diode at 940 nm. Furthermore, we discuss250 W single-crystal fiber Yb:YAG laser Xavier Délen,1, * Stefan Piehler,2 Julien Didierjean,3 demonstrate an Yb:YAG single-crystal fiber laser with 251 W output power in continuous-wave and an optical

Paris-Sud XI, Université de

380

Effective symmetry and physical properties of twinned perovskite ferroelectric single crystals  

E-print Network

symmetry is in general different from the microscopic symmetry of the crystal when it is not in a single crystal symmetry belongs to the rhombohedral 3m with dipoles formed in 111 family of the parent cubicEffective symmetry and physical properties of twinned perovskite ferroelectric single crystals Jirí

Cao, Wenwu

381

NMR studies of H 2 single crystals. VI. Line shapes in the orientationally ordered phase  

Microsoft Academic Search

We report the first experimental and theoretical study of the NMR lineshape anisotropy in the orientationally ordered cubic phase of H2 single crystals. After a brief review of the orientational phase diagram for ortho-para mixtures, we describe in detail the various cubic crystal structures that are obtained after a transformation from an initial single hcp crystal. We then calculate the

A. B. Harris; S. Washburn; H. Meyer

1983-01-01

382

Single-crystal II-VI on Si single-junction and tandem solar cells  

Microsoft Academic Search

CdTe is one of the leading materials used in solar photovoltaics. However, the maximum reported CdTe cell efficiencies are considerably lower than the theoretically expected efficiencies for the ~1.48 eV CdTe band gap. We report a class of single crystal CdTe-based solar cells grown epitaxially on crystalline Si that show promise for enhancing the efficiency and greatly lowering the cost

M. Carmody; S. Mallick; J. Margetis; R. Kodama; T. Biegala; D. Xu; P. Bechmann; J. W. Garland; S. Sivananthan

2010-01-01

383

PHYSICAL REVIEW B 84, 035315 (2011) Theoretical analysis of the crystal structure, band-gap energy, polarization, and piezoelectric  

E-print Network

.65.-j I. INTRODUCTION ZnO thin films and one-dimensional nanostructures have gained significant, single crystals, thin films, and nanostructures.1,2,6 Due to these properties, ZnO is a key enabling material in sensors and actuators, transparent thin-film electronics, and optoelectronic and piezoelectric

Alpay, S. Pamir

384

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Structural and Electrical Properties of Single Crystalline Ga-Doped ZnO Thin Films Grown by Molecular Beam Epitaxy  

NASA Astrophysics Data System (ADS)

High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a-plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about one electron per Ga dopant when the Ga concentration is no more than 2%. However, further increasing the Ga doping concentration leads to a decrease of the conductivity due to partial segregation of Ga atoms to the minor phase of the spinel ZnGa2O4 or other intermediate phase. It seems that the maximum solubility of Ga in the ZnO single crystalline film is about 2 at.% and the lowest resistivity can reach 1.92 × 10-4 ?·cm at room temperature, close to the best value reported. In contrast to ZnO:Ga thin film with 1% or 2% Ga doping, the film with 4% Ga doping exhibits a metal semiconductor transition at 80 K. The scattering mechanism of conducting electrons in single crystalline ZnO:Ga thin film is discussed.

Lu, Zhong-Lin; Zou, Wen-Qin; Xu, Ming-Xiang; Zhang, Feng-Ming; Du, You-Wei

2009-11-01

385

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

386

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

387

Single-Crystal Elasticity of Ettringite at ambient conditions  

NASA Astrophysics Data System (ADS)

Ettringite, [Ca6Al2 (SO4)3 (OH)12^{.}26H2O] is a natural trigonal sulfate and one of the most relevant crystalline components of Portland cement. It is both a primary crystalline product during cement paste consolidation and a secondary phase which develops during concrete degradation. Even though the understanding of the mechanical properties of cement paste and of consolidated concrete is a longstanding problem of engineering and materials science, we still have a poor knowledge of the physical properties of ettringite. This makes it difficult to develop quantitative models able to predict the behavior and properties of such a complex multi-component system. We have now determined the single-crystal elastic constants of natural ettringite by Brillouin spectroscopy at ambient conditions. Brillouin scattering was measured along 54 different directions from two 2 mm size platelets of approximate orientation (001) and (100) prepared from a large single crystal of ettringite from South Africa. The six non-zero single-crystal elastic constants of this trigonal mineral are: C11 = 35.1(1) GPa, C12 = 21.9(1) GPa, C13 = 20.0(5) GPa, C14 = 0.6(2) GPa, C_{33 = 55(1) GPa, C44 = 11.0(2) GPa. The Hill average of the aggregate bulk and shear modulus are 27.3(9) GPa and 9.9(1) GPa respectively, more than 35 percent smaller than the moduli of gypsum. Ettringite possesses a large elastic anisotropy, with a difference of 50 percent between the Young's modulus along the stiff c- axis and the a- axis. The rigidity in planes containing the c- axis is 40 percent higher than in the basal plane. The pattern of elastic anisotropy in ettringite is directly connected to its crystallographic structure and to its external morphology. In fact, stiff chains of [Al(OH) 6]^{3-} octahedra alternating with triplets of Ca2+ in eight-fold coordination run parallel to the c- axis. Development of secondary fibrous ettringite elongated parallel to c- axis might play a major role as a mechanism for concrete weakening and deterioration.

Speziale, S.; Jiang, F.; Mao, Z.; Monteiro, P. J.; Wenk, H.; Duffy, T. S.; Schilling, F.

2006-12-01

388

Growth and characterization of organometallic l-alanine cadmium chloride single crystal by slow evaporation technique  

Microsoft Academic Search

Single crystals of l-alanine cadmium chloride (LACC), an organometallic nonlinear optical material, have been grown by the slow evaporation technique. The grown crystals were subjected to various characterization techniques, such as single crystal and powder XRD, FTIR, UV–vis and TGA-DTA. The mechanical properties of the crystals show that this material belongs to the category of hard materials. Second harmonic generation

K. C. Bright; T. H. Freeda

2010-01-01

389

Growth and characterization of organometallic L-alanine cadmium chloride single crystal by slow evaporation technique  

Microsoft Academic Search

Single crystals of L-alanine cadmium chloride (LACC), an organometallic nonlinear optical material, have been grown by the slow evaporation technique. The grown crystals were subjected to various characterization techniques, such as single crystal and powder XRD, FTIR, UV-vis and TGA-DTA. The mechanical properties of the crystals show that this material belongs to the category of hard materials. Second harmonic generation

K. C. Bright; T. H. Freeda

2010-01-01

390

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

391

Solidification microstructures in single-crystal stainless steel melt pools  

SciTech Connect

Development of microstructure of stationary melt pools of oriented stainless steel single crystals (70%Fe-15%Ni-15%Cr was analyzed. Stationary melt pools were formed by electron-beam and gas-tungsten-arc heating on (001), (011), and (111) oriented planes of the austenitic, fcc-alloy crystals. Characterization and analysis of resulting microstructure was carried out for each crystallographic plane and welding method. Results showed that crystallography which favors ``easy growth`` along the <100> family of directions is a controlling factor in the microstructural formation along with the melt-pool shape. The microstructure was found to depend on the melting method, since each method forms a unique melt-pool shape. These results are used in making a three-dimensional reconstruction of the microstructure for each plane and melting method employed. This investigation also suggests avenues for future research into the microstructural properties of electron-beam welds as well as providing an experimental basis for mathematical models for the prediction of solidification microstructures.

Sipf, J.B.; Boatner, L.A.; David, S.A.

1994-03-01

392

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

393

Textures in Single-Crystal Aluminum Friction Stir Spot Welds  

NASA Astrophysics Data System (ADS)

The present article examines the textural features produced during friction stir spot welding of single-crystal aluminum sheet. The crystal has the {111} plane perpendicular to the normal direction (ND) of the sheet, and the left< { 1 10} rightrangle direction parallel to the growth direction (GD). Friction stir spot welding was carried out using a rotation speed of 1500 rpm and a dwell time of 2 seconds, and completed spot welds were characterized using a combination of optical microscopy and electron backscatter diffraction (EBSD). The EBSD measurements indicate there are no significant changes in orientation in locations more than 840 ?m from the stir-zone extremity. The orientation distribution in the thermomechanically-affected zone (TMAZ) region conformed with the {110}?ND orientation within 580 ?m of the stir-zone extremity. In the location immediately adjacent to the stir-zone extremity, there was a deviation from the {110}//ND orientation due to a combination of compressive loading perpendicular to the stir-zone boundary and shear loading in the direction of tool rotation. It is suggested a {111}?ND texture in the stir zone is associated with material flow imposed by the thread on the rotating pin.

Shibayanagi, Toshiya; Gerlich, Adrian P.; Kashihara, Keizo; North, Thomas H.

2009-04-01

394

Redetermination of olivenite from an untwinned single-crystal.  

PubMed

The crystal structure of olivenite, ideally Cu(2)(AsO(4))(OH) [dicopper(II) arsenate(V) hydroxide], was redetermined from an untwinned and phosphate-containing natural sample, composition Cu(2)(As(0.92)P(0.08)O(4)), from Majuba Hill (Nevada, USA). Olivenite is structurally analogous with the important rock-forming mineral andalusite, Al(2)OSiO(4). Its structure consists of chains of edge-sharing, distorted [CuO(4)(OH)(2)] octa-hedra extending parallel to [001]. These chains are cross-linked by isolated AsO(4) tetra-hedra through corner-sharing, forming channels in which dimers of edge-sharing [CuO(4)(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

395

Elastic stability of high coupling ternary single crystals  

NASA Astrophysics Data System (ADS)

A sub-hertz harmonic force was used to investigate the elastic response of ternary (1-y-x)Pb(In1/2Nb1/2)O3-yPb(Mg1/3Nb2/3)O3-xPbTiO3 (PIN-PMN-PT) single crystal with compositions (x = 0.30 and x = 0.33) near the Morphotropic Phase Boundary (MPB) under isothermal and zero-field conditions. The observed instability under mechanical compression is attributable to a ferroelectric rhombohedral FR-ferroelectric orthorhombic FO phase transformation. The associated strain is a function of proximity to MPB and is consistent with the prediction of the classical Devonshire theory. Isothermal resonance-antiresonance frequency sweeps versus temperature revealed a non-vertical MPB with (?TRT/?x)<0, where TRT is the rhombohedral-tetragonal transition temperature. These results provide insights into the role of PT content on the stability of PIN-PMN-PT crystals used for electromechanical devices and sound projectors.

Finkel, Peter; Murphy, Colin J.; Stace, Joseph; Bussmann, Konrad; Heitmann, Adam; Amin, Ahmed

2013-05-01

396

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

397

Electronic properties of ?-FeSi2 -- single crystal study  

NASA Astrophysics Data System (ADS)

The discovery of high temperature superconductivity (HTS) in Fe pnictides has simulated a lot of work in field of Fe-based materials. We focus on the tetragonal (high-temperature) form of the iron disilicide, which crystal structure resembles one of the HTS, LiFeAs (Tsc=18 K). Single crystals of ?-FeSi2 with Fe0.83Si2 composition were grown and magnetic, transport and heat capacity studies were performed in consistent way. Magnetic susceptibility of ?-FeSi2 increases in a linear fashion with increasing temperature, as was commonly observed among Fe HTS. In a contrast to superconducting pnictides, where ?(T) ˜ T is associated to antiferromagnetic fluctuations, in ?-FeSi2 this behavior is rather related to the electronic structure of this metal. In Fe-based HTS proximity of the SDW instability seems to be crucial for the emergence of superconducting state -- in ?-FeSi2 the experimental data do not find evidence for any strong electronic correlations. Our LDA and DMFT calculations results find low density of states, supporting weakness of correlations and suggest electronic configuration of Fe close to d^6.

Miiller, Wojciech; Tomczak, Jan; Simonson, Jack; Smith, Greg; Aronson, Meigan

2013-03-01

398

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

399

Crystal growth, structural, thermal and mechanical behavior of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals.  

PubMed

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. PMID:24967545

Mahadevan, M; Ramachandran, K; Anandan, P; Arivanandhan, M; Bhagavannarayana, G; Hayakawa, Y

2014-12-10

400

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

401

Superconductivity in SrNi2P2 single crystals  

SciTech Connect

Heat capacity, magnetic susceptibility, and resistivity of SrNi{sub 2}P{sub 2} single crystals are presented, illustrating the structural transition at 325 K, and bulk superconductivity at 1.4 K. The magnitude of {Tc}, fits to the heat capacity data, the small upper critical field H{sub c2} = 390 Oe, and {kappa} = 2.1 suggests a conventional fully gapped superconductor. With applied pressure we find that superconductivity persists into the so-called 'collapsed tetragonal' phase, although the transition temperature is monotonically suppressed with increasing pressure. This argues that reduced dimensionality can be a mechanism for increasing the transition temperatures of layered NiP, as well as layered FeAs and NiAs, superconductors.

Ronning, Filip [Los Alamos National Laboratory; Bauer, Eric D [Los Alamos National Laboratory; Park, Tuscon [Los Alamos National Laboratory; Thompson, Joe D [Los Alamos National Laboratory

2009-01-01

402

InPBi Single Crystals Grown by Molecular Beam Epitaxy  

NASA Astrophysics Data System (ADS)

InPBi was predicted to be the most robust infrared optoelectronic material but also the most difficult to synthesize within In-VBi (V = P, As and Sb) 25 years ago. We report the first successful growth of InPBi single crystals with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InPBi thin films reveal excellent surface, structural and optical qualities making it a promising new III-V compound family member for heterostructures. The Bi concentration is found to be 2.4 +/- 0.4% with 94 +/- 5% Bi atoms at substitutional sites. Optical absorption indicates a band gap of 1.23 eV at room temperature while photoluminescence shows unexpectedly strong and broad light emission at 1.4-2.7 ?m which can't be explained by the existing theory.

Wang, K.; Gu, Y.; Zhou, H. F.; Zhang, L. Y.; Kang, C. Z.; Wu, M. J.; Pan, W. W.; Lu, P. F.; Gong, Q.; Wang, S. M.

2014-06-01

403

Analysis of ripple formation in single crystal spot welds  

NASA Technical Reports Server (NTRS)

Stationary spot welds have been made at the (001) surface of Fe-l5%Ni-15%Cr single crystals using a Gas Tungsten Arc (GTA). On the top surface of the spot welds, very regular and concentric ripples were observed after solidification by differential interference color microscopy. Their height (typically 1--5 micrometers and spacing, typically approximately 60 micrometers) decreased with the radius of the pool. These ripples were successfully accounted for in terms of capillary-wave theory using the fundamental mode frequency f(sub 0) given by the first zero of the zero-order Bessel function. The spacing d between the ripples was then equated to v(sub s)/f(sub 0), where v(sub s) is the solidification rate. From the measured ripple spacing, the velocity of the pool was deduced as a function of the radius, and this velocity was in good agreement with the results of a heat-flow simulation.

Rappaz, M.; Corrigan, D.; Boatner, L. A.

1997-01-01

404

Ambient Compression-Compression Fatigue Behavior of Magnesium Single Crystal  

NASA Astrophysics Data System (ADS)

A magnesium single crystal sample with a near orientation was tested at room temperature under compression-compression cyclic loading, and the microstructure was characterized to disclose the involved deformation mechanisms. No plastic deformation region appeared on the stress-strain curve during the cyclic loading. The stress-strain curve stabilized at the first cycle, the strain range for each cycle fluctuated slightly around a constant value, and the mean strain for each cycle was in a narrow range from 0.0846 to 0.0863 during the whole test. The ratcheting strain rate decreased exponentially from ~0.0003, and reached a relatively small and stable value of about zero. The observed deformation mechanisms were prismatic slip, compression twinning, and tension twinning. The prismatic dislocation slip roughened the cylindrical sample surface by forming extrusions and intrusions, and small cracks were also observed on the surface.

Li, Qizhen

2014-01-01

405

InPBi Single Crystals Grown by Molecular Beam Epitaxy  

PubMed Central

InPBi was predicted to be the most robust infrared optoelectronic material but also the most difficult to synthesize within In-VBi (V = P, As and Sb) 25 years ago. We report the first successful growth of InPBi single crystals with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InPBi thin films reveal excellent surface, structural and optical qualities making it a promising new III–V compound family member for heterostructures. The Bi concentration is found to be 2.4 ± 0.4% with 94 ± 5% Bi atoms at substitutional sites. Optical absorption indicates a band gap of 1.23?eV at room temperature while photoluminescence shows unexpectedly strong and broad light emission at 1.4–2.7??m which can't be explained by the existing theory. PMID:24965260

Wang, K.; Gu, Y.; Zhou, H. F.; Zhang, L. Y.; Kang, C. Z.; Wu, M. J.; Pan, W. W.; Lu, P. F.; Gong, Q.; Wang, S. M.

2014-01-01

406

Ultrathin aluminum sample cans for single crystal inelastic neutron scattering  

SciTech Connect

Single crystal inelastic neutron scattering measurements are often performed using a sample environment for controlling sample temperature. One difficulty associated with this is establishing appropriate thermal coupling from the sample to the temperature controlled portion of the sample environment. This is usually accomplished via a sample can which thermally couples the sample environment to the sample can and the sample can to the sample via an exchange gas. Unfortunately, this can will contribute additional background signal to ones measurement. We present here the design of an ultrathin aluminum sample can based upon established technology for producing aluminum beverage cans. This design minimizes parasitic sample can scattering. Neutron scattering measurements comparing a machined sample can to our beverage can design clearly indicate a large reduction in scattering intensity and texture when using the ultrathin sample can design. We also examine the possibility of using standard commercial beverage cans as sample cans.

Stone, Matthew B [ORNL; Loguillo, Mark [ORNL; Abernathy, Douglas L [ORNL

2011-01-01

407

Radionuclide annular single crystal scintillator camera with rotating collimator  

SciTech Connect

A radionuclide emission tomography camera is described for sensing gamma ray emissions from a source within the field of view consisting of: a fixed, position-sensitive detector means, responsive to the gamma ray emissions and surrounding the field of view for detecting the contact position and the trajectory from which a gamma ray emission originates, the fixed, position-sensitive detector including a single continuous stationary scintillation crystal; rotatable collimator means, disposed between the fixed, position-sensitive detecto means and the field of view, and including at least one array of collimator elements, for restricting and collimating the gamma ray emissions; and means for rotating the collimator means relative to the fixed, position-sensitive detector, for exposing different sections of the position-sensitive detector to the gamma ray emissions in order to view the source from different angles.

Genna, S.; Pang, S.-C.

1986-04-22

408

Ferroelectricity in single crystal InMnO3  

NASA Astrophysics Data System (ADS)

Single crystal synthesis, structure, electric polarization, and heat capacity measurements on hexagonal InMnO3 show that this small R ion in the RMnO3 series is ferroelectric (space group P63cm). Structural analysis of this system reveals a high degree of order within the MnO5 polyhedra but significant distortions in the R-O bond distributions compared to the previously studied materials. Point-charge estimates of the electric polarization yield an electrical polarization of ˜7.8 ?C/cm2, 26% larger than the well-studied YMnO3 system. This system with enhanced room temperature polarization values may serve as a possible replacement for YMnO3 in device applications.

Yu, T.; Gao, P.; Wu, T.; Tyson, T. A.; Lalancette, R.

2013-04-01

409

Electrical conduction in nanodomains in congruent lithium tantalate single crystal  

NASA Astrophysics Data System (ADS)

The electrical current flow behavior was investigated for nanodomains formed in a thin congruent lithium tantalate (LiTaO3) single-crystal plate. When the nanodomains were relatively large, with diameters of about 100 nm, current flow was detected along the domain wall. However, when they were about 40 nm or smaller, the current flowed through the entire nanodomain. Schottky-like rectifying behavior was observed. Unlike the case of LiNbO3, optical illumination was not required for current conduction in LiTaO3. A clear temperature dependence of the current was found indicating that the conduction mechanism for nanodomains in LiTaO3 may involve thermally activated carrier hopping.

Cho, Yasuo

2014-01-01

410

Protective CVD Mullite Coatings on Single-Crystal Silicon Substrates  

NASA Astrophysics Data System (ADS)

Silicon has long been the primary material of choice for microelectromechanical systems (MEMS) and integrated circuit (IC) applications. However, it is prone to degradation under severe conditions such as high humidity, high temperature, and corrosive environments. To overcome such extreme conditions and help silicon perform with stability and extended lifetimes, a protection layer is proposed. Mullite (3Al2O3·2SiO2) is a known environmental barrier coating (EBC) material and has been shown to be effective on other Si-based ceramic materials. In this work, dense, high-purity crystalline mullite coatings were deposited onto single-crystal silicon substrates via chemical vapor deposition (CVD). The microstructure, orientation preference, and adhesion of these coatings were investigated. Substrate integrity in relation to the substrate/coating interface by chemical etching and coating stability in a simulated severe environment under corrosive alkali salts were investigated.

Xu, Jiapeng; Erickson, Daniel; Roy, Sudesna; Sarin, Vinod

2013-04-01

411

Toward Optimum Scale and TBC Adhesion on Single Crystal Superalloys  

NASA Technical Reports Server (NTRS)

Single crystal superalloys exhibit excellent cyclic oxidation resistance if their sulfur content is reduced from typical impurity levels of approximately 5 ppmw to below 0.5 ppmw. Excellent alumina scale adhesion was documented for PWA 1480 and PWA 1484 without yttrium additions. Hydrogen annealing produced effective desulfurization of PWA 1480 to less than 0.2 ppmw and was also used to achieve controlled intermediate levels. The direct relationship between cyclic oxidation behavior and sulfur content was shown. An adhesion criterion was proposed based on the total amount of sulfur available for interfacial segregation, e.g., less than or equal to 0.2 ppmw S will maximize adhesion for a 1 mm thick sample. PWA 1484, melt desulfurized to 0.3 ppmw S, also exhibited excellent cyclic oxidation resistance and encouraging TBC lives (10 mils of 8YSZ, plasma sprayed without a bond coat) in 1100 C cyclic oxidation tests.

Smialek, James L.

1998-01-01

412

Growth and characterization of L-serine formate nonlinear optical single crystal  

NASA Astrophysics Data System (ADS)

A novel organic nonlinear optical single crystal L-Serine Formate (LSF) was successfully grown by solution growth using the slow evaporation technique. The structure of the grown crystal has been determined by single crystal X-ray diffraction analysis. The presence of functional groups in LSF crystal has been identified by FTIR spectrum. The crystal is transparent over entire visible region. The second harmonic generation efficiency of the grown LSF crystal has been obtained by the Kurtz-Perry powder technique. The laser induced surface damage threshold value 6.836 GW/cm2 indicates that this material can be used for high-power laser applications.

Krishnan, P.; Gayathri, K.; Anbalagan, G.

2013-02-01

413

Electrical Conductivity of Hydrous Single Crystal San Carlos Olivine  

NASA Astrophysics Data System (ADS)

The electrical conductivity of anhydrous San Carlos olivine is too low to explain the observed electrical conductivity of Earth's upper mantle. Although the solubility of hydrogen in olivine is relatively low at mantle P and T conditions, it has been estimated that even at concentrations of less than 1000 ppm, electrical conductivity is enhanced by as much as a factor of one hundred, based on a conduction mechanism involving hydrogen diffusion (Karato, Nature 347, 272-273, 1990). In this study we have measured the electrical conductivity of hydrated San Carlos olivine single crystals, oriented along (100), (010) and (001). SCO single crystals were first oriented, machined into 2 mm diameter cylinders, and then sandwiched between layers of a talc+brucite mix in sealed Pt capsules for hydration runs at pressures up to 8 GPa and 1200°C in a multianvil apparatus. Recovered samples were then cut into wafers ranging from 0.2 to 0.6 mm in thickness for subsequent complex impedance measurements to determine electrical conductivity, also carried out at high pressure. For the electrical measurements, temperatures were limited to about 700°C in order to minimize loss of water from the sample. FTIR spectroscopy was used to determine water content of samples both before and after the electrical measurements. Preliminary results indicate that at concentrations of a few hundred ppm water, conductivities are several orders of magnitude higher than for dry olivine. Activation energies decrease with increasing water content, indicating that extrapolation of conductivities to higher temperatures leads to a smaller overall effect. However, based on these results, at upper mantle conditions, the presence of minor amounts of hydrogen in olivine is sufficient to bridge the gap between the conductivity of dry olivine and that of the mantle.

Poe, B.; Romano, C.; Nestola, F.; Rubie, D.

2005-12-01

414

Comparative study of intrinsic luminescence in undoped transparent ceramic and single crystal garnet scintillators  

NASA Astrophysics Data System (ADS)

Scintillation properties associated with intrinsic lattice defects of undoped Y3A5O12 (YAG) and Lu3A5O12 (LuAG) transparent ceramics and single crystals are compared. The ceramics excited with X-ray demonstrated relatively low emission intensity when compared with that of the single crystals. Decay times of the ceramics and the single crystals were similar. These parameters were approximately 430 ns (YAG ceramic), 460 ns (YAG single crystal), 30 ns and 1090 ns (LuAG ceramic), and 25 ns and 970 ns (LuAG single crystal). According to the pulse height spectra recorded under 137Cs gamma-ray irradiation, the scintillation light yield of the both ceramics were about 2950 ± 290 ph/MeV. However, the single crystals had greater kight yield of about about 14,300 ± 1430 ph/MeV for YAG and 8350 ± 830 ph/MeV for LuAG.

Fujimoto, Yutaka; Yanagida, Takayuki; Yagi, Hideki; Yanagidani, Takagimi; Chani, Valery

2014-10-01

415

Method for the preparation of inorganic single crystal and polycrystalline electronic materials  

NASA Technical Reports Server (NTRS)

Large area, semiconductor crystals selected from group 3-5 compounds and alloys are provided for semiconductor device fabrication by the use of a selective etching operation which completely removes the substrate on which the desired crystal was deposited. The substrate, selected from the same group as the single crystal, has a higher solution rate than the epitaxial single crystal which is essentially unaffected by the etching solution. The preparation of gallium phosphide single crystals using a gallium arsenide substrate and a concentrated nitric acid etching solution is described.

Groves, W. O. (inventor)

1969-01-01

416

Fabrication of ZnO photonic crystals by nanosphere lithography using inductively coupled-plasma reactive ion etching with CH{sub 4}/H{sub 2}/Ar plasma on the ZnO/GaN heterojunction light emitting diodes  

SciTech Connect

This article reports fabrication of n-ZnO photonic crystal/p-GaN light emitting diode (LED) by nanosphere lithography to further booster the light efficiency. In this article, the fabrication of ZnO photonic crystals is carried out by nanosphere lithography using inductively coupled plasma reactive ion etching with CH{sub 4}/H{sub 2}/Ar plasma on the n-ZnO/p-GaN heterojunction LEDs. The CH{sub 4}/H{sub 2}/Ar mixed gas gives high etching rate of n-ZnO film, which yields a better surface morphology and results less plasma-induced damages of the n-ZnO film. Optimal ZnO lattice parameters of 200 nm and air fill factor from 0.35 to 0.65 were obtained from fitting the spectrum of n-ZnO/p-GaN LED using a MATLAB code. In this article, we will show our recent result that a ZnO photonic crystal cylinder has been fabricated using polystyrene nanosphere mask with lattice parameter of 200 nm and radius of hole around 70 nm. Surface morphology of ZnO photonic crystal was examined by scanning electron microscope.

Chen, Shr-Jia; Chang, Chun-Ming; Kao, Jiann-Shiun; Chen, Fu-Rong; Tsai, Chuen-Horng [Engineering and System Science, National Tsing Hua University, Hsinchu, 30013 Taiwan (China); Instrument Technology Research Center, National Applied Research Laboratories, Hsinchu, 300 Taiwan (China); Engineering and System Science, National Tsing Hua University, Hsinchu, 30013 Taiwan (China)

2010-07-15

417

Melting of polymer single crystals studied by dynamic Monte Carlo simulations  

Microsoft Academic Search

We report dynamic Monte Carlo simulations of lattice polymers melting from a metastable chain-folded lamellar single crystal.\\u000a The single crystal was raised and then melted in an ultrathin film of polymers wetting on a solid substrate, mimicking the\\u000a melting observations made by using Atomic Force Microscopy. We observed that the thickness distribution of the single crystal\\u000a appears quite inhomogeneous and

Y. Ren; A. Ma; J. Li; X. Jiang; Y. Ma; A. Toda; W. Hu

2010-01-01

418

Dielectric response of PMN–0.32PT single crystal and ceramics under dc electric field  

Microsoft Academic Search

The temperature dependences of dielectric properties for [001] PMN–0.32PT single crystal and PMN–0.32PT ceramics under different dc electric field (E) have been investigated. A new monoclinic phase can be induced by electric field with E=1.5–4.0kV\\/cm, while heating, in [001] PMN–0.32PT single crystal. The phase transition process of single crystal is from rhombohedral to monoclinic, then from monoclinic to tetragonal, finally

Zhenrong Li; Zhuo Xu; Zengzhe Xi; Xi Yao

2004-01-01

419

Single-crystal organic field effect transistors with the hole mobility ?8cm2\\/V s  

Microsoft Academic Search

We report on the fabrication and characterization of single-crystal organic p-type field-effect transistors (OFETs) with the field-effect mobility ??8cm2\\/V s, substantially higher than that observed in thin-film OFETs. The single-crystal devices compare favorably with thin-film OFETs not only in this respect: the mobility for the single-crystal devices is nearly independent of the gate voltage and the field effect onset is

V. Podzorov; S. E. Sysoev; E. Loginova; V. M. Pudalov; M. E. Gershenson

2003-01-01

420

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

421

Centers of photosensitivity in ZnO  

NASA Astrophysics Data System (ADS)

To reveal recombination centers responsible for ZnO UV photosensitivity, combined investigations of photoconductivity (PC) and photoluminescence (PL) spectra were performed in nominally undoped ZnO single crystals. In PL spectra, green (500 nm), orange (620 nm) and red (720 nm) bands related to deep levels were present, the greater the relative intensity of orange band the higher the photosensitivity. After removal of exciting light, PL afterglow as well as PC "tail" took place at 77 K. It was found that decay time of PC "tail" coincided with that of orange band afterglow and was essentially longer than the afterglow decay times of green and red bands. The conclusion was made that recombination centers responsible for the orange band were the centers of photosensitivity. In addition, a strong influence of electron traps on steady-state PC was shown.

Markevich, I. V.; Kushnirenko, V. I.; Borkovska, L. V.; Bulakh, B. M.; Sheinkman, M. K.; Prokopenko, I. V.

2007-11-01

422

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

423

Growth and characterization of isotopically enriched {sup 70}Ge and {sup 74}Ge single crystals  

SciTech Connect

Isotopically enriched {sup 70}Ge and {sup 74}Ge single crystals were successfully gown by a newly developed vertical Bridgman method. The system allows us to reliably grow high purity Ge single crystals of approximately 1 cm{sup 3} volume. To our knowledge, we have grown the first {sup 70}Ge single crystal. The electrically active chemical impurity concentration for both crystals was found to be {approximately}2 {times} cm{sup {minus}3} which is two order of magnitude better that of {sup 74}Ge crystals previously grown by two different groups. Isotopic enrichment of the {sup 70}Ge and the {sup 74}Ge crystals is 96.3% and 96.8%, respectively. The residual chemical impurities present in both crystals were identified as phosphorus, copper, aluminum, and indium. A wide variety of experiments which take advantage of the isotopic purity of our crystals are discussed.

Itoh, K.

1992-10-01

424

Growth behavior of L-pyrrolidone-2-carboxylic acid (L-PCA) single crystals  

NASA Astrophysics Data System (ADS)

Growth conditions to prepare large single crystals of L-pyrrolidone-2-carboxylic acid (L-PCA), a novel nonlinear optical organic material, have been intensively studied with an attempt for fabrication in optical devices. L-PCA single crystals of good optical quality having dimensions of typically ~ 2.5 × 1.5 ×1.5 cm 3 were grown from aqueous solutions with seed crystals by a slow cooling method. They are chemically stable because molecules are hydrogen bonded to form three-dimensional networks in the crystal state. Further growth conditions to obtain large single crystals in a shorter time have been investigated by considering both mass balance equations and the kinetics for crystal growth. It was found that increasing the cooling rate in the later periods of crystal growth is advantageous for the purpose. The largest crystal was 17.5 g in weight, which was prepared in 6 days.

Kitazawa, Manabu; Takahashi, Mitsuo; Matsuoka, Masakuni

1994-08-01

425

Growth and characterization of isotopically enriched [sup 70]Ge and [sup 74]Ge single crystals  

SciTech Connect

Isotopically enriched [sup 70]Ge and [sup 74]Ge single crystals were successfully gown by a newly developed vertical Bridgman method. The system allows us to reliably grow high purity Ge single crystals of approximately 1 cm[sup 3] volume. To our knowledge, we have grown the first [sup 70]Ge single crystal. The electrically active chemical impurity concentration for both crystals was found to be [approximately]2 [times] cm[sup [minus]3] which is two order of magnitude better that of [sup 74]Ge crystals previously grown by two different groups. Isotopic enrichment of the [sup 70]Ge and the [sup 74]Ge crystals is 96.3% and 96.8%, respectively. The residual chemical impurities present in both crystals were identified as phosphorus, copper, aluminum, and indium. A wide variety of experiments which take advantage of the isotopic purity of our crystals are discussed.

Itoh, K.

1992-10-01

426

CCMR: Growth of Olivine Single Crystals for Point Defect and Transport Investigations  

NSDL National Science Digital Library

Using the float-zone technique and an image furnace, single crystals of the olivine compound Mn2SiO4 were grown to be used for defect-related properties analysis. The crystals grown so far are not of high enough quality to perform this analysis on; however, the crystals are well suited for producing oriented seed crystals for later high quality crystal growth. The crystals were grown with the aid of a ceramic afterheater. This type of afterheater proved effective at growing crack-free single crystals, and the use of an afterheater is planned to be implemented for all further growth of high-quality single crystals of Mn2SiO4.

Maier, Mitchell

2010-08-15

427

Electron paramagnetic resonance study of radiation damage in isonipecotic acid single crystal  

NASA Astrophysics Data System (ADS)

The electron spin resonance spectra of the radical produced by gamma-irradiation of a single crystal of isonipecotic acid (piperidine-4-carboxylic acid) were reported, and the structure of the radical was discussed. Isonipecotic acid single crystals were exposed to 60Co-gamma irradiation at room temperature. The irradiated single crystals were investigated by Electron Paramagnetic Resonance (EPR) Spectroscopy between 115 K and 300 K. The spectra were found to be temperature independent. The g values of the radiation damage center observed in isonipecotic acid single crystal and the hyperfine structure constants of the free electron with nearby protons were obtained.

Caliskan, Betul; Caliskan, Ali Cengiz; Yerli, Rabia

2014-10-01

428

Piezoelectric properties of domain engineered barium titanate single crystals with different volume fractions of domain walls  

PubMed Central

A piezoelectric domain wall model has been developed to analyze the effective piezoelectric properties of domain engineered BaTiO3 (BT) single crystals with different volume fractions of 90° domain walls. The model takes into account the nonuniform deformation in the domain wall region, which can create additional anisotropy to enhanced functional properties of multidomain single crystals. Our theoretical results indicate that a larger volume fraction of domain walls will produce larger effective piezoelectric coefficients. In addition, with the increase in domain wall volume fraction, [011]c poled BT single crystals will have a much larger piezoelectric property enhancement than [111]c poled BT single crystals. PMID:19865498

Xiang, Yang; Zhang, Rui; Cao, Wenwu

2009-01-01

429

From single crystal surfaces to single atoms: investigating active sites in electrocatalysis  

NASA Astrophysics Data System (ADS)

Electrocatalytic processes will undoubtedly be at the heart of energising future transportation and technology with the added importance of being able to create the necessary fuels required to do so in an environmentally friendly and cost effective manner. For this to be successful two almost mutually exclusive surface properties need to be reconciled, namely producing highly active/reactive surface sites that exhibit long term stability. This article reviews the various approaches which have been undertaken to study the elusive nature of these active sites on metal surfaces which are considered as adatoms or clusters of adatoms with low coordination number. This includes the pioneering studies at extended well defined stepped single crystal surfaces using cyclic voltammetry up to the highly sophisticated in situ electrochemical imaging techniques used to study chemically synthesised nanomaterials. By combining the information attained from single crystal surfaces, individual nanoparticles of defined size and shape, density functional theory calculations and new concepts such as mesoporous multimetallic thin films and single atom electrocatalysts new insights into the design and fabrication of materials with highly active but stable active sites can be achieved. The area of electrocatalysis is therefore not only a fascinating and exciting field in terms of realistic technological and economical benefits but also from the fundamental understanding that can be acquired by studying such an array of interesting materials.

O'Mullane, Anthony P.

2014-03-01

430

Investigation on crystalline perfection, mechanical, piezoelectric and ferroelectric properties of L-tartaric acid single crystal  

NASA Astrophysics Data System (ADS)

Polar organic nonlinear optical material, L-tartaric acid single crystals have been grown from slow evaporation solution growth technique. Single crystal X-ray diffraction study indicates that the grown crystal crystallized in monoclinic system with space group P21. Crystalline perfection of the crystal has been evaluated by high resolution X-ray diffraction technique and it reveals that the crystal quality is good and free from structural grain boundaries. Mechanical stability of the crystal has been analyzed by Vickers microhardness measurement and it exhibits reverse indentation size effect. Piezoelectric d33 co-efficient for the crystal has been examined and its value is 47 pC/N. The ferroelectric behaviour of the crystal was analyzed by polarization-electric field hysteresis loop measurement.

Murugan, G. Senthil; Ramasamy, P.

2014-04-01

431

Studies on the Growth, Spectral, Optical and Thermal Properties of 4-NITROANILINE Picrate Single Crystals  

NASA Astrophysics Data System (ADS)

In this paper, an organic 4-nitroaniline picrate (4NP) single crystal was grown by solution growth method. Single crystal X-ray diffraction study revealed that grown crystal belongs to orthorhombic system with Pbcn space group. The solid state constants such as plasma energy, Penn gap, Fermi energy and polarizability of 4NP crystal were determined theoretically. The functional groups of the grown crystals were confirmed qualitatively from FTIR spectral analysis. The thermal decomposition and melting point of the crystal were determined from thermogravimetric analysis. The optical absorption and cut-off wavelength of the crystal were determined from UV-visible study. The second harmonic generation (SHG) efficiency of the grown crystal was measured by Kurtz-Perry SHG test using Nd:YAG laser. The laser damage threshold value of the grown crystal was estimated by multi-shot method using 1064 nm laser.

Sivakumar, P. K.; Kumar, M. Krishna; Kumar, R. Mohan; Kanagadurai, R.

2013-12-01

432

Polymorphic single crystal {r_reversible} single crystal transition in K{sub 0.975}Rb{sub 0.025}NO{sub 3}  

SciTech Connect

Polymorphic transformations in K{sub 0.975}Rb{sub 0.025}NO{sub 3} single crystals have been investigated by optical microscopy and X-ray diffraction. The equilibrium temperature between modifications II and III has been determined. It is established that the crystal growth at II {r_reversible} III polymorphic transitions is accompanied by the formation and growth of daughter-modification nuclei in the matrix crystal.

Asadov, Yu. G., E-mail: yusifasadov@rambler.ru; Nasirov, E. V. [Azerbaijan National Academy of Sciences, Institute of Physics (Azerbaijan)

2010-09-15

433

Broadband ZnO Single-Nanowire Light-Emitting Diode  

Microsoft Academic Search

We present a novel technique for reliable electrical injection into single semiconductor nanowires for light-emitting diodes and lasers. The method makes use of a high-resolution negative electron-beam resist and direct electron-beam patterning for the precise fabrication of a metallic top contact along the length of the nanowire, while a planar substrate is used as a bottom contact. It can be

Jiming Bao; Mariano A. Zimmler; Federico Capasso; Xiaowei Wang; Z. F. Ren

2006-01-01

434

Magnetism in Ar-implanted ZnO  

NASA Astrophysics Data System (ADS)

ZnO single crystals were implanted with Ar ions with an energy of 100 keV and different fluences. Ferromagnetic behaviour is observed at room temperature after implantation. This behaviour is suppressed after consecutive annealings at 400 and 500 °C. Although trace transition metal impurities have been identified in the virgin samples, it is shown that they cannot account for the observed magnetic behaviour that is assigned to the presence of implantation-induced lattice defects.

Borges, R. P.; da Silva, R. C.; Magalhães, S.; Cruz, M. M.; Godinho, M.

2007-11-01

435

Barrier inhomogeneity in Ag Schottky contacts to bulk ZnO grown by different methods  

NASA Astrophysics Data System (ADS)

The electrical properties of Ag Schottky contacts to differently grown bulk ZnO single crystals were comparatively investigated. Schottky contacts to O-polar ZnO revealed higher barrier heights and lower ideality factors than those to Zn-polar ZnO. A higher degree of oxidation at the Ag-ZnO interface might occur for the O-polar ZnO, increasing the barrier heights. Compared to the current values measured under vacuum, those measured in an air ambient were decreased, suggesting that compensation of the surface conductive layer by acceptor-like adsorbates such as O2 and H2O plays an important role in the current transport of Ag/ZnO contacts.

Kim, Hogyoung; Sohn, Ah-Rum; Kim, Dong-Wook

2012-02-01

436

High spatial resolution ZnO scintillator for an in situ imaging device in EUV region  

NASA Astrophysics Data System (ADS)

A single shot image of a ZnO crystal excited by the EUV laser of Kansai Photon Science Institute was captured. The evaluated EUV beam waist radii from the ZnO emission pattern along the horizontal and vertical axes are 5.0 and 4.7 ?m, respectively. The expected focal spot si