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Sample records for gan prime yu

  1. Prime Knowledge about Primes

    ERIC Educational Resources Information Center

    Eisenberg, Theodore

    2007-01-01

    Several proofs demonstrating that there are infinitely many primes, different types of primes, tests of primality, pseudo primes, prime number generators and open questions about primes are discussed in Section 1. Some of these notions are elaborated upon in Section 2, with discussions of the Riemann zeta function and how algorithmic complexity…

  2. Swift Captures Asteroid 2005 YU55 Flyby

    NASA Video Gallery

    Asteroid 2005 YU55 whisks through the field of view of Swift's Ultraviolet/Optical Telescope (UVOT) on Nov. 9, just hours after the space rock made its closest approach to Earth. The video plays on...

  3. GaN HEMTs

    NASA Astrophysics Data System (ADS)

    Anderson, Jonathan W.; Lee, Kyoung-Keun; Piner, Edwin L.

    2012-03-01

    Gallium nitride (GaN) has enormous potential for applications in high electron mobility transistors (HEMTs) used in RF and power devices. Intrinsic device properties such as high electron mobility, high breakdown voltage, very high current density, electron confinement in a narrow channel, and high electron velocity in the 2-dimensional electron gas of the HEMT structure are due in large part to the wide band gap of this novel semiconductor material system. This presentation discusses the properties of GaN that make it superior to other semiconductor materials, and outlines the research that will be undertaken in a new program at Texas State University to advance GaN HEMT technology. This program's aim is to further innovate the exceptional performance of GaN through improved material growth processes and epitaxial structure design.

  4. Immunity of PCB transplacental Yu-Cheng children in Taiwan

    SciTech Connect

    Lan, Shou Jen; Yen, Yea Yin; Chen, Eng Rin; Ko, Ying Chin ); Lan, Joung Liang )

    1990-02-01

    Up to now, there has been no studies about the immune status of PCB transplacental Yu-Cheng babies. In an earlier study, Yu-Cheng babies were reported to have a high infant mortality rate. It was reported that these babies would easily catch cold, experience diarrhea and abdominal pains. Recently, it was found that the bronchitis rate of Yu-Cheng babies is higher than in control babies. Because of high risk of infection, it is presumed that these babies might suffer immunosuppression to a certain extent. According to these findings, investigations into the immune functions of PCB transplacental Yu-Cheng babies are needed.

  5. Growth of GaN- and ZnO-Based Nanorod Compound Structures

    DTIC Science & Technology

    2013-08-16

    growth region. 33 Part III: Related Journal Publication List (acknowledging AOARD) 1. Chih-Yen Chen, Wen-Ming Chang , Wei-Lun Chung, Chieh Hsieh ...Che-Hao Liao, Wen-Ming Chang , Yu-Feng Yao, Hao-Tsung Chen, Chia-Ying Su, Chih-Yen Chen, Chieh Hsieh , Horng-Shyang Chen, Charng-Gan Tu, Yean-Woei...p. 28418~28430, 17 December 2012. (SCI) 10. Chieh Hsieh , Horng-Shyang Chen, Che-Hao Liao, Chih-Yen Chen, Chun-Han Lin, Cheng- Hung Lin, Shao-Ying

  6. The AKAP Yu is required for olfactory long-term memory formation in Drosophila.

    PubMed

    Lu, Yubing; Lu, Yi-Sheng; Shuai, Yichun; Feng, Chunhua; Tully, Tim; Xie, Zuoping; Zhong, Yi; Zhou, Hai-Meng

    2007-08-21

    Extensive neurogenetic analysis has shown that memory formation depends critically on cAMP-protein kinase A (PKA) signaling. Details of how this pathway is involved in memory formation, however, remain to be fully elucidated. From a large-scale behavioral screen in Drosophila, we identified the yu mutant to be defective in one-day memory after spaced training. The yu mutation disrupts a gene encoding an A-kinase anchoring protein (AKAP). AKAPs comprise a family of proteins, which determine the subcellular localization of PKAs and thereby critically restrict cAMP signaling within a cell. Further behavioral characterizations revealed that long-term memory (LTM) was disrupted specifically in the yu mutant, whereas learning, short-term memory and anesthesia-resistant memory all appeared normal. Another independently isolated mutation of the yu gene failed to complement the LTM defect associated with the yu mutation, and this phenotypic defect could be rescued by induced acute expression of a yu(+) transgene, suggesting that yu functions physiologically during memory formation. AKAP Yu is expressed preferentially in the mushroom body (MB) neuroanatomical structure, and expression of a yu(+) transgene to the MB, but not to other brain regions, is sufficient to rescue the LTM defect of the yu mutant. These observations lead us to conclude that proper localization of PKA by Yu AKAP in MB neurons is required for the formation of LTM.

  7. Learning about Primes

    ERIC Educational Resources Information Center

    McEachran, Alec

    2008-01-01

    In this article, the author relates his unhappy experience in learning about prime numbers at secondary school. To introduce primes, a teacher first told students a definition of a prime number, then students were taught how to find prime numbers. Students defined and listed them and at some later point were tested on their memory of both the…

  8. Motor Priming in Neurorehabilitation

    PubMed Central

    Stoykov, Mary Ellen; Madhavan, Sangeetha

    2014-01-01

    Priming is a type of implicit learning wherein a stimulus prompts a change in behavior. Priming has been long studied in the field of psychology. More recently, rehabilitation researchers have studied motor priming as a possible way to facilitate motor learning. For example, priming of the motor cortex is associated with changes in neuroplasticity that are associated with improvements in motor performance. Of the numerous motor priming paradigms under investigation, only a few are practical for the current clinical environment, and the optimal priming modalities for specific clinical presentations are not known. Accordingly, developing an understanding of the various types of motor priming paradigms and their underlying neural mechanisms is an important step for therapists in neurorehabilitation. Most importantly, an understanding of the methods and their underlying mechanisms is essential for optimizing rehabilitation outcomes. The future of neurorehabilitation is likely to include these priming methods, which are delivered prior to or in conjunction with primary neurorehabilitation therapies. In this Special Interest article we discuss those priming paradigms that are supported by the greatest amount of evidence including: (i) stimulation-based priming, (ii) motor imagery and action observation, (iii) sensory priming, (iv) movement-based priming, and (v) pharmacological priming. PMID:25415551

  9. [On the contribution of Prof. Yu. S. Balashov to the fundamental parasitology].

    PubMed

    Ryss, A Iu

    2013-01-01

    Brief review of main conceptions of Yu. S. Balasov in fundamental parasitology: types of host-parasite relations, evolution, transmissive infections, econiches, population structure, parasite communities.

  10. Dynamics analysis of fractional order Yu-Wang system

    NASA Astrophysics Data System (ADS)

    Bhalekar, Sachin

    2013-10-01

    Fractional order version of a dynamical system introduced by Yu and Wang (Engineering, Technology & Applied Science Research, 2, (2012) 209-215) is discussed in this article. The basic dynamical properties of the system are studied. Minimum effective dimension 0.942329 for the existence of chaos in the proposed system is obtained using the analytical result. For chaos detection, we have calculated maximum Lyapunov exponents for various values of fractional order. Feedback control method is then used to control chaos in the system. Further, the system is synchronized with itself and with fractional order financial system using active control technique. Modified Adams-Bashforth-Moulton algorithm is used for numerical simulations.

  11. Orbital Picture of Yu-Shiba-Rusinov Multiplets

    NASA Astrophysics Data System (ADS)

    Ruby, Michael; Peng, Yang; von Oppen, Felix; Heinrich, Benjamin W.; Franke, Katharina J.

    2016-10-01

    We investigate the nature of Yu-Shiba-Rusinov (YSR) subgap states induced by single manganese (Mn) atoms adsorbed on different surface orientations of superconducting lead (Pb). Depending on the adsorption site, we detect a distinct number and characteristic patterns of YSR states around the Mn atoms. We suggest that the YSR states inherit their properties from the Mn d levels, which are split by the surrounding crystal field. The periodicity of the long-range YSR oscillations allows us to identify a dominant coupling of the d states to the outer Fermi sheet of the two-band superconductor Pb.

  12. GaN High Power Devices

    SciTech Connect

    PEARTON,S.J.; REN,F.; ZHANG,A.P.; DANG,G.; CAO,X.A.; LEE,K.P.; CHO,H.; GILA,B.P.; JOHNSON,J.W.; MONIER,C.; ABERNATHY,C.R.; HAN,JUNG; BACA,ALBERT G.; CHYI,J.-I.; LEE,C.-M.; NEE,T.-E.; CHUO,C.-C.; CHI,G.C.; CHU,S.N.G.

    2000-07-17

    A brief review is given of recent progress in fabrication of high voltage GaN and AlGaN rectifiers, GaN/AlGaN heterojunction bipolar transistors, GaN heterostructure and metal-oxide semiconductor field effect transistors. Improvements in epitaxial layer quality and in fabrication techniques have led to significant advances in device performance.

  13. Bulk ammonothermal GaN

    NASA Astrophysics Data System (ADS)

    Dwiliński, R.; Doradziński, R.; Garczyński, J.; Sierzputowski, L. P.; Puchalski, A.; Kanbara, Y.; Yagi, K.; Minakuchi, H.; Hayashi, H.

    2009-05-01

    In this work, results of structural characterization of high-quality ammonothermal GaN are presented. Besides expected low dislocation density (being of the order of 10 3 cm -2) the most interesting feature seems perfect flatness of the crystal lattice of studied crystals. Regardless the size of crystals, lattice curvature radius exceeds 100 m, whereas better crystals reveal radius of several hundred meters and the best above 1000 m. Excellent crystallinity manifests in very narrow X-ray diffraction peaks of full-width at half-maximum (FWHM) values about 16 arcsec.

  14. Yu-Gong Yi Shan: Exploring Some Possibilities of Designing Tomorrow's Foreign Language Textbook.

    ERIC Educational Resources Information Center

    Chan, Chung; Liu, Li-chia

    1992-01-01

    An electronic version of Yu-gong Yi Shan, an ancient Chinese fable, is discussed as a prototype of the use of technology for Chinese teaching and learning. Yu-gong demonstrates how hypermedia can be designed to overcome the linear, static, and silent constraints of book technology. (four references) (Author/LB)

  15. An ERP investigation of orthographic priming with superset primes.

    PubMed

    Ktori, Maria; Midgley, Katherine; Holcomb, Phillip J; Grainger, Jonathan

    2015-01-12

    Prime stimuli formed by inserting unrelated letters in a given target word (called "superset" primes) provide a means to modify the relative positions of the letters shared by prime and target. Here we examined the time-course of superset priming effects in an ERP study using the sandwich-priming paradigm. We compared the effects of superset primes formed by the insertion of unrelated letters (e.g., maurkdet-MARKET), or by the insertion of hyphens (e.g., ma-rk-et-MARKET), with identity priming (e.g., market-MARKET), all measured relative to unrelated control primes. Behavioral data revealed significantly greater priming in the hyphen-insert condition compared with the letter-insert condition. In the ERP signal, letter-insert priming emerged later than hyphen-insert priming and produced a reversed priming effect in the N400 time-window compared with the more typical N400 priming effects seen for both hyphen-insert priming and identity priming. The different pattern of priming effects seen for letter-insert primes and hyphen-insert primes suggests that compared with identity priming, letter superset priming reflects the joint influence of: (1) a disruption in letter position information, and (2) an inhibitory influence of mismatching letters.

  16. Bulk GaN Ion Cleaving

    NASA Astrophysics Data System (ADS)

    Moutanabbir, O.; Gösele, U.

    2010-05-01

    Bulk or freestanding GaN is a key material in various devices other than the blue laser diodes. However, the high cost of bulk GaN wafers severely limits the large scale exploitation of these potential technologies. In this paper, we discuss some engineering issues involved in the application of the ion-cut process to split a thin layer from 2-inch freestanding GaN. This process combines the implantation of light ions and wafer bonding and can possibly be used to reduce the cost of the fabrication of GaN-based devices by allowing the transfer of several bulk quality thin layers from the same donor wafer. To achieve this multi-layer transfer several conditions must be fulfilled. Here issues related to bulk GaN surface irregularities and wafer bowing are discussed. We also describe a method to circumvent most of these problems and achieve high quality bonding.

  17. Optical properties of GaN pyramids

    SciTech Connect

    Zeng, K.C.; Lin, J.Y.; Jiang, H.X.; Yang, W.

    1999-03-01

    Picosecond time-resolved photoluminescence (PL) spectroscopy has been used to investigate the optical properties of GaN pyramids overgrown on hexagonal-patterned GaN(0001) epilayers on sapphire and silicon substrates with AlN buffer layers. We found that: (i) the release of the biaxial compressive strain in GaN pyramids on GaN/AlN/sapphire substrate led to a 7 meV redshift of the spectral peak position with respect to the strained GaN epilayer grown under identical conditions; (ii) in the GaN pyramids on GaN/AlN/sapphire substrate, strong band edge transitions with much narrower linewidths than those in the GaN epilayer have been observed, indicating the improved crystalline quality of the overgrown pyramids; (iii) PL spectra taken from different parts of the pyramids revealed that the top of the pyramid had the highest crystalline quality; and (iv) the presence of strong band-to-impurity transitions in the pyramids were primarily due to the incorporation of the oxygen and silicon impurities from the SiO{sub 2} mask. {copyright} {ital 1999 American Institute of Physics.}

  18. Nanoair-bridged lateral overgrowth of GaN on ordered nanoporous GaN template

    NASA Astrophysics Data System (ADS)

    Wang, Y. D.; Zang, K. Y.; Chua, S. J.; Tripathy, S.; Chen, P.; Fonstad, C. G.

    2005-12-01

    We report the growth of high-quality GaN epilayers on an ordered nanoporous GaN template by metalorganic chemical vapor deposition. The nanopores in GaN template were created by inductively coupled plasma etching using anodic aluminum oxide film as an etch mask. The average pore diameter and interpore distance is about 65 and 110nm, respectively. Subsequent overgrowth of GaN first begins at the GaN crystallite surface between the pores, and then air-bridge-mediated lateral overgrowth leads to the formation of the continuous layer. Microphotoluminescence and micro-Raman measurements show improved optical properties and significant strain relaxation in the overgrown layer when compared to GaN layer of same thickness simultaneously grown on sapphire without any template. Similar to conventional epitaxial lateral overgrown GaN, such overgrown GaN on a nanopatterned surface would also serve as a template for the growth of ultraviolet-visible light-emitting III-nitride devices.

  19. Priming Gestures with Sounds

    PubMed Central

    Lemaitre, Guillaume; Heller, Laurie M.; Navolio, Nicole; Zúñiga-Peñaranda, Nicolas

    2015-01-01

    We report a series of experiments about a little-studied type of compatibility effect between a stimulus and a response: the priming of manual gestures via sounds associated with these gestures. The goal was to investigate the plasticity of the gesture-sound associations mediating this type of priming. Five experiments used a primed choice-reaction task. Participants were cued by a stimulus to perform response gestures that produced response sounds; those sounds were also used as primes before the response cues. We compared arbitrary associations between gestures and sounds (key lifts and pure tones) created during the experiment (i.e. no pre-existing knowledge) with ecological associations corresponding to the structure of the world (tapping gestures and sounds, scraping gestures and sounds) learned through the entire life of the participant (thus existing prior to the experiment). Two results were found. First, the priming effect exists for ecological as well as arbitrary associations between gestures and sounds. Second, the priming effect is greatly reduced for ecologically existing associations and is eliminated for arbitrary associations when the response gesture stops producing the associated sounds. These results provide evidence that auditory-motor priming is mainly created by rapid learning of the association between sounds and the gestures that produce them. Auditory-motor priming is therefore mediated by short-term associations between gestures and sounds that can be readily reconfigured regardless of prior knowledge. PMID:26544884

  20. Recognizing Plant Defense Priming.

    PubMed

    Martinez-Medina, Ainhoa; Flors, Victor; Heil, Martin; Mauch-Mani, Brigitte; Pieterse, Corné M J; Pozo, Maria J; Ton, Jurriaan; van Dam, Nicole M; Conrath, Uwe

    2016-10-01

    Defense priming conditions diverse plant species for the superinduction of defense, often resulting in enhanced pest and disease resistance and abiotic stress tolerance. Here, we propose a guideline that might assist the plant research community in a consistent assessment of defense priming in plants.

  1. Priming Ability Emotional Intelligence

    ERIC Educational Resources Information Center

    Schutte, Nicola S.; Malouff, John M.

    2012-01-01

    Two studies examined whether priming self-schemas relating to successful emotional competency results in better emotional intelligence performance. In the first study participants were randomly assigned to a successful emotional competency self-schema prime condition or a control condition and then completed an ability measure of emotional…

  2. Discovery: Prime Numbers

    ERIC Educational Resources Information Center

    de Mestre, Neville

    2008-01-01

    Prime numbers are important as the building blocks for the set of all natural numbers, because prime factorisation is an important and useful property of all natural numbers. Students can discover them by using the method known as the Sieve of Eratosthenes, named after the Greek geographer and astronomer who lived from c. 276-194 BC. Eratosthenes…

  3. PRIME Lab Radiocarbon Measurements

    NASA Astrophysics Data System (ADS)

    Hillegonds, D. J.; Mueller, K. A.; Ma, X.; Lipschutz, M. E.

    1996-03-01

    The Purdue Rare Isotope Measurement Laboratory (PRIME Lab) is one of three NSF national facilities for accelerator mass spectrometry (AMS), and is the only one capable of determining six cosmogenic radionuclides: 10Be, 14C, 26Al, 36Cl, 41Ca, and 129I. This abstract describes the current status of the radiocarbon analysis program at PRIME Lab.

  4. Building Numbers from Primes

    ERIC Educational Resources Information Center

    Burkhart, Jerry

    2009-01-01

    Prime numbers are often described as the "building blocks" of natural numbers. This article shows how the author and his students took this idea literally by using prime factorizations to build numbers with blocks. In this activity, students explore many concepts of number theory, including the relationship between greatest common factors and…

  5. The Formation and Characterization of GaN Hexagonal Pyramids

    NASA Astrophysics Data System (ADS)

    Zhang, Shi-Ying; Xiu, Xiang-Qian; Lin, Zeng-Qin; Hua, Xue-Mei; Xie, Zi-Li; Zhang, Rong; Zheng, You-Dou

    2013-05-01

    GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method. Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviolet illumination, producing submicron-sized pyramids. Hexagonal pyramids on the etched GaN with well-defined {101¯1¯} facets and very sharp tips are formed. High-resolution x-ray diffraction shows that etched GaN with pyramids has a higher crystal quality, and micro-Raman spectra reveal a tensile stress relaxation in GaN with pyramids compared with normal GaN. The cathodoluminescence intensity of GaN after etching is significantly increased by three times, which is attributed to the reduction in the internal reflection, high-quality GaN with pyramids and the Bragg effect.

  6. Largest known twin primes and Sophie Germain primes

    NASA Astrophysics Data System (ADS)

    Indlekofer, Karl-Heinz; Járai, Antal

    The numbers 242206083* 2^38880+-1 are twin primes. The number p=2375063906985* 2^19380-1 is a Sophie Germain prime, i.e. p and 2p+1 are both primes. For p=4610194180515* 2^ 5056-1, the numbers p, p+2 and 2p+1 are all primes.

  7. Masked priming effect reflects evidence accumulated by the prime.

    PubMed

    Kinoshita, Sachiko; Norris, Dennis

    2010-01-01

    In the same-different match task, masked priming is observed with the same responses but not different responses. Norris and Kinoshita's (2008) Bayesian reader account of masked priming explains this pattern based on the same principle as that explaining the absence of priming for nonwords in the lexical decision task. The pattern of priming follows from the way the model makes optimal decisions in the two tasks; priming does not depend on first activating the prime and then the target. An alternative explanation is in terms of a bias towards responding "same" that exactly counters the facilitatory effect of lexical access. The present study tested these two views by varying both the degree to which the prime predicts the response and the visibility of the prime. Unmasked primes produced effects expected from the view that priming is influenced by the degree to which the prime predicts the response. In contrast, with masked primes, the size of priming for the same response was completely unaffected by predictability. These results rule out response bias as an explanation of the absence of masked priming for different responses and, in turn, indicate that masked priming is not a consequence of automatic lexical access of the prime.

  8. Mushroom structure of GaN template for epitaxial growth of GaN

    NASA Astrophysics Data System (ADS)

    Lee, Sung Bo; Kwon, Tae-Wan; Park, Jungwon; Jin Choi, Won; Sung Park, Hae

    2012-07-01

    In the present study, we show the formation of mushroom morphology produced by a ramp anneal of a low-temperature GaN buffer layer. Structural analysis by transmission electron microscopy indicates that the cap of the mushroom has the stable wurtzitic GaN structure, whereas the stem possesses the metastable zinc-blende structure. With the air gap introduced between the substrate and the cap of the mushroom structure, threading dislocations propagate along its stem. The formation of the mushroom morphology is suggested to result from the nucleation of wurtzitic GaN on the surface of the low-temperature buffer layer during the ramp anneal, followed by mass transport of GaN from the buffer layer, which remains zinc-blende during the anneal, to the surface, because wurtzitic GaN has the lower structure energy than zinc-blende GaN. This study extends limits of the conventional use of the buffer layer, laying the foundation for the development of low-cost recipes for achieving GaN templates with a low density of threading dislocations.

  9. Theoretical study of gallium nitride molecules, GaN2 and GaN4.

    PubMed

    Tzeli, Demeter; Theodorakopoulos, Giannoula; Petsalakis, Ioannis D

    2008-09-18

    The electronic and geometric structures of gallium dinitride GaN 2, and gallium tetranitride molecules, GaN 4, were systematically studied by employing density functional theory and perturbation theory (MP2, MP4) in conjunction with the aug-cc-pVTZ basis set. In addition, for the ground-state of GaN 4( (2)B 1) a density functional theory study was carried out combining different functionals with different basis sets. A total of 7 minima have been identified for GaN 2, while 37 structures were identified for GaN 4 corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces and bonding mechanisms for some low-lying electronic states of GaN 4. The dissociation energy of the ground-state GaN 2 ( X (2)Pi) is 1.1 kcal/mol with respect to Ga( (2)P) + N 2( X (1)Sigma g (+)). The ground-state and the first two excited minima of GaN 4 are of (2)B 1( C 2 v ), (2)A 1( C 2 v , five member ring), and (4)Sigma g (-)( D infinityh ) symmetry, respectively. The dissociation energy ( D e) of the ground-state of GaN 4, X (2)B 1, with respect to Ga( (2)P) + 2 N 2( X (1)Sigma g (+)), is 2.4 kcal/mol, whereas the D e of (4)Sigma g (-) with respect to Ga( (4)P) + 2 N 2( X (1)Sigma g (+)) is 17.6 kcal/mol.

  10. How important is a prime's gestalt for subliminal priming?

    PubMed

    Jaśkowski, Piotr; Slósarek, Maciej

    2007-06-01

    Masked stimuli (primes) can affect the preparation of a motor response to subsequently presented target stimuli. Under some conditions, reactions to the main stimulus can be facilitated (straight priming) or inhibited (inverse priming) when preceded by a compatible prime (calling for the same response). In the majority of studies in which inverse priming was demonstrated arrows pointing left or right were used as prime and targets. There is, however, evidence that arrows are special overlearned stimuli which are processed in a favorable way. Here we report three experiments designated to test whether the "arrowness" of primes/targets is a sufficient condition for inverse priming. The results clearly show that although inverse priming appeared when non-arrow shapes were used, the magnitude of the priming effect was larger with arrows. The possible reasons for this effect are discussed.

  11. Resonantly enhanced selective photochemical etching of GaN

    NASA Astrophysics Data System (ADS)

    Trichas, E.; Kayambaki, M.; Iliopoulos, E.; Pelekanos, N. T.; Savvidis, P. G.

    2009-04-01

    Wavelength dependent photochemical etching of GaN films reveals a strong resonant enhancement of the photocurrent at the GaN gap, in close agreement with the excitonic absorption profile of GaN. The corresponding etching rate of GaN strongly correlates with the measured photocurrent. No photocurrent, nor etching is observed for AlGaN films under same excitation conditions. The method could pave the way to the development of truly selective etching of GaN on AlGaN for the fabrication of nitride based optoelectronic devices.

  12. Growth of self-standing GaN substrates

    NASA Astrophysics Data System (ADS)

    Lee, Hyun-Jae; Fujii, Katsushi; Goto, Takenari; Kim, Chinkyo; Chang, Jiho; Hong, Soon-Ku; Cho, Meoungwhan; Yao, Takafumi

    2010-03-01

    Large-sized and high-quality free standing GaN are required with the development of GaN-based devices. We have developed new techniques to reduce the price of GaN substrates. In this paper, we introduce a simple fabrication way of freestanding GaN substrate using hydride vapor phase epitaxy (HVPE). An evaporable buffer layer was applied for the fabrication of 2inch freestanding GaN to separate from a sapphire substrate, in other words, a freestanding GaN was fabricated only by HVPE (one-stop process) without any process.

  13. Mechanism of Torrential Rain Associated with the Mei-yu Development during SCSMEX-98

    NASA Technical Reports Server (NTRS)

    Qian, Jian-Hua; Tao, Wei-Kuo; Lau, K.-M.; Starr, David OC. (Technical Monitor)

    2002-01-01

    A case of torrential precipitation process in the Mei-yu front, an Asian monsoon system east to the Tibetan Plateau, is studied with the coupled Penn State University/NCAR MM5 and NASA/GSFC PLACE (Parameterization for Land - Atmosphere - Cloud Exchange) models. Remote and local impacts of water vapor on the location and intensity of Mei-yu precipitation are studied by numerical experiments. Results demonstrate that the water vapor source for this heavy precipitation case in Yangtze river basin is derived mostly from the Bay of Bengal, transported by the southwesterly low-level Jet (LLJ) southeast to the Tibetan Plateau. The moist convection is a critical process in the development and maintenance of the front. The meridional and zonal secondary circulations resulted from Mei-yu condensation heating both act to increase the wind speed in the LLJ. The condensation induced local circulation strengthens the moisture transport in the LLJ, providing a positive feedback to sustain the Mei-yu precipitation system. It is found that local precipitation recycling shifts heavy rain toward the warm side of the Mei-yu front. This shift of rainfall location is due to the pronounced increase of atmospheric moisture and decrease of surface temperature over the warm side of the front.

  14. GaN membrane MSM ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Muller, A.; Konstantinidis, G.; Kostopoulos, A.; Dragoman, M.; Neculoiu, D.; Androulidaki, M.; Kayambaki, M.; Vasilache, D.; Buiculescu, C.; Petrini, I.

    2006-12-01

    GaN exhibits unique physical properties, which make this material very attractive for wide range of applications and among them ultraviolet detection. For the first time a MSM type UV photodetector structure was manufactured on a 2.2 μm. thick GaN membrane obtained using micromachining techniques. The low unintentionally doped GaN layer structure was grown by MOCVD on high resistivity (ρ>10kΩcm) <111> oriented silicon wafers, 500μm thick. The epitaxially grown layers include a thin AlN layer in order to reduce the stress in the GaN layer and avoid cracking. Conventional contact lithography, e-gun Ni/Au (10nm /200nm) evaporation and lift-off techniques were used to define the interdigitated Schottky metalization on the top of the wafer. Ten digits with a width of 1μm and a length of 100μm were defined for each electrode. The distance between the digits was also 1μm. After the backside lapping of the wafer to a thickness of approximately 150μm, a 400nm thick Al layer was patterned and deposited on the backside, to be used as mask for the selective reactive ion etching of silicon. The backside mask, for the membrane formation, was patterned using double side alignment techniques and silicon was etched down to the 2.2μm thin GaN layer using SF 6 plasma. A very low dark current (30ρA at 3V) was obtained. Optical responsivity measurements were performed at 1.5V. A maximum responsivity of 18mA/W was obtained at a wavelength of 370nm. This value is very good and can be further improved using transparent contacts for the interdigitated structure.

  15. Prime Retrieval of Motor Responses in Negative Priming

    ERIC Educational Resources Information Center

    Mayr, Susanne; Buchner, Axel; Dentale, Sandra

    2009-01-01

    Three auditory identification experiments were designed to specify the prime-response retrieval model of negative priming (S. Mayr & A. Buchner, 2006), which assumes that the prime response is retrieved in ignored repetition trials and interferes with probe responding. In Experiment 1, shortly before (in Experiment 1A) or after (in Experiment 1B)…

  16. "Fell" Primes "Fall", but Does "Bell" Prime "Ball"? Masked Priming with Irregularly-Inflected Primes

    ERIC Educational Resources Information Center

    Crepaldi, Davide; Rastle, Kathleen; Coltheart, Max; Nickels, Lyndsey

    2010-01-01

    Recent masked priming experiments have brought to light a morphological level of analysis that is exclusively based on the orthographic appearance of words, so that it breaks down corner into corn- and -er, as well as dealer into deal- and -er (Rastle, Davis, & New, 2004). Being insensitive to semantic factors, this morpho-orthographic…

  17. Prime-Time Nutrition.

    ERIC Educational Resources Information Center

    Kaufman, Lois

    1980-01-01

    Presents a study identifying, analyzing, and describing messages on prime-time network television related to food, eating behavior, and ideal body image. Program content and commercials studied present conflicting messages: (1) that we eat in ways almost guaranteed to make us fat, and (2) that we strive to remain too slim. (JMF)

  18. Gallium Nitride (GaN) High Power Electronics (FY11)

    DTIC Science & Technology

    2012-01-01

    Gallium Nitride (GaN) High Power Electronics (FY11) by Kenneth A. Jones, Randy P. Tompkins, Michael A. Derenge, Kevin W. Kirchner, Iskander...Army Research Laboratory Adelphi, MD 20783-1197 ARL-TR-5903 January 2012 Gallium Nitride (GaN) High Power Electronics (FY11) Kenneth A...DSI 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Gallium Nitride (GaN) High Power Electronics (FY11) 5a. CONTRACT NUMBER 5b. GRANT

  19. Masked Repetition Priming Using Magnetoencephalography

    ERIC Educational Resources Information Center

    Monahan, Philip J.; Fiorentino, Robert; Poeppel, David

    2008-01-01

    Masked priming is used in psycholinguistic studies to assess questions about lexical access and representation. We present two masked priming experiments using MEG. If the MEG signal elicited by words reflects specific aspects of lexical retrieval, then one expects to identify specific neural correlates of retrieval that are sensitive to priming.…

  20. Rhizosphere priming: a nutrient perspective

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rhizosphere priming is the change in decomposition of soil organic matter (SOM) caused by root activity. Rhizosphere priming plays a crucial role in soil carbon (C) dynamics and their response to global climate change. Rhizosphere priming may be affected by soil nutrient availability, but rhizospher...

  1. Priming Ditransitive Structures in Comprehension

    ERIC Educational Resources Information Center

    Arai, Manabu; van Gompel, Roger P. G.; Scheepers, Cristoph

    2007-01-01

    Many studies have shown evidence for syntactic priming during language production (e.g., Bock, 1986). It is often assumed that comprehension and production share similar mechanisms and that priming also occurs during comprehension (e.g., Pickering & Garrod, 2004). Research investigating priming during comprehension (e.g., Branigan et al., 2005 and…

  2. Language Ideology in Taiwan: The KMT's Language Policy, the Tai-yu Language Movement, and Ethnic Politics.

    ERIC Educational Resources Information Center

    Hsiau, A-chin

    1997-01-01

    Analyzes the official (Kuomintang) language policy in Taiwan, which had exalted Mandarin and suppressed other local languages, and the efforts during the last decade to revive Tai-yu, a major language in the post-war period. The dynamics of the Tai-yu language movement reveal a pressing problem facing Taiwan: how to balance national cohesion with…

  3. Dislocation annihilation in regrown GaN on nanoporous GaN template with optimization of buffer layer growth

    NASA Astrophysics Data System (ADS)

    Soh, C. B.; Hartono, H.; Chow, S. Y.; Chua, S. J.; Fitzgerald, E. A.

    2007-01-01

    Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nanoscale pores of size 20-50nm in the underlying grains. The effect of GaN buffer layer grown at various temperatures from 650to1015°C on these as-fabricated nanopores templates is investigated by transmission electron microscopy. The buffer layer grown at the optimized temperature of 850°C partially fill up the pores and voids with annihilation of threading dislocations, serving as an excellent template for high-quality GaN growth. This phenomenon is, however, not observed for the samples grown with other temperature buffer layers. Micro-Raman measurements show significant strain relaxation and improvement in the crystal quality of the overgrown GaN layer on nanoporous GaN template as compared to overgrown on conventional GaN template.

  4. Amphoteric arsenic in GaN

    SciTech Connect

    Wahl, U.; Correia, J. G.; Araujo, J. P.; Rita, E.; Soares, J. C.

    2007-04-30

    The authors have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive {sup 73}As. They give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fact that As{sub Ga} 'antisites' are not minority defects provide additional aspects to be taken into account for an explanantion of the so-called miscibility gap in ternary GaAs{sub 1-x}N{sub x} compounds, which cannot be grown with a single phase for values of x in the range of 0.1

  5. [Exploration of Yu Shen-chu's achievements in pharmacology and his academic idea].

    PubMed

    Hua, Bi-Chun

    2003-01-01

    Prof. Yu not only explored the origin of Chinese materia medica and its development, but also emphasized the education and popularization of Chinese, materia medica. He was arduous in practicing, summarizing, and writing of Chinese material medica and devoted all his life to the development and ducation of TCM. He was conversant with both TCM and Chinese pharmacology.

  6. Semantic priming of familiar songs.

    PubMed

    Johnson, Sarah K; Halpern, Andrea R

    2012-05-01

    We explored the functional organization of semantic memory for music by comparing priming across familiar songs both within modalities (Experiment 1, tune to tune; Experiment 3, category label to lyrics) and across modalities (Experiment 2, category label to tune; Experiment 4, tune to lyrics). Participants judged whether or not the target tune or lyrics were real (akin to lexical decision tasks). We found significant priming, analogous to linguistic associative-priming effects, in reaction times for related primes as compared to unrelated primes, but primarily for within-modality comparisons. Reaction times to tunes (e.g., "Silent Night") were faster following related tunes ("Deck the Hall") than following unrelated tunes ("God Bless America"). However, a category label (e.g., Christmas) did not prime tunes from within that category. Lyrics were primed by a related category label, but not by a related tune. These results support the conceptual organization of music in semantic memory, but with potentially weaker associations across modalities.

  7. TEM characterization of GaN nanowires

    SciTech Connect

    Liliental-Weber, Zuzanna; Gao, Y.H.; Bando, Y.

    2002-02-21

    Transmission electron microscopy was applied to study GaN nanowires grown on carbon nanotube surfaces by chemical reaction between Ga{sub 2}O and NH{sub 3} gas in a conventional furnace. These wires grew in two crystallographic directions, <2{und 11}0> and <01{und 1}0> (fast growth directions of GaN), in the form of whiskers covered by small elongated GaN platelets. The morphology of these platelets is similar to that observed during the growth of single crystals from a Ga melt at high temperatures under high nitrogen pressure. It is thought that growth of nanowires in two different crystallographic directions and the arrangement of the platelets to the central whisker may be influenced by the presence of Ga{sub 2}O{sub 3} (based on the observation of the energy dispersive x-ray spectra), the interplanar spacings in the wire, and the presence of defects on the interface between the central part of the nanowire and the platelets surrounding it.

  8. Two primes priming: does feature integration occur before response activation?

    PubMed

    Grainger, Julianne E; Scharnowski, Frank; Schmidt, Thomas; Herzog, Michael H

    2013-07-17

    Responses to a target can be sped up or slowed down by a congruent or incongruent prime, respectively. Even though presentations are rapid, the prime and the target are thought to activate motor responses in strict sequence, with prime activation preceding target activation. In feature fusion, the opposite seems to be the case. For example, a vernier offset to the left is immediately followed by a vernier offset to the right at the same location. The two verniers are not perceived as two elements in sequence but as a single, aligned vernier. Here, we ask the question as to how features are integrated: before or after motor activation? We presented two vernier primes with opposite offset directions preceding a single vernier target. No priming effect occurred when the vernier primes were presented at the same location, indicating that verniers integrate before motor activation. There was also no priming effect when the primes were presented simultaneously at different locations, indicating that there is an integration stage different from the perceptual fusion stage. When the second prime is delayed, it determines priming, even for very long delays. To explain these long integration times, we argue that there is a buffer preceding motor activation.

  9. P-type doping of GaN

    SciTech Connect

    Wong, Raechelle Kimberly

    2000-04-01

    After implantation of As, As + Be, and As + Ga into GaN and annealing for short durations at temperatures as high as 1500 C, the GaN films remained highly resistive. It was apparent from c-RBS studies that although implantation damage did not create an amorphous layer in the GaN film, annealing at 1500 C did not provide enough energy to completely recover the radiation damage. Disorder recovered significantly after annealing at temperatures up to 1500 C, but not completely. From SIMS analysis, oxygen contamination in the AIN capping layer causes oxygen diffusion into the GaN film above 1400 C. The sapphire substrate (A1203) also decomposed and oxygen penetrated into the backside of the GaN layer above 1400 C. To prevent donor-like oxygen impurities from the capping layer and the substrate from contaminating the GaN film and compensating acceptors, post-implantation annealing should be done at temperatures below 1500 C. Oxygen in the cap could be reduced by growing the AIN cap on the GaN layer after the GaN growth run or by depositing the AIN layer in a ultra high vacuum (UHV) system post-growth to minimize residual oxygen and water contamination. With longer annealing times at 1400 C or at higher temperatures with a higher quality AIN, the implantation drainage may fully recover.

  10. GaN Electronics For High Power, High Temperature Applications

    SciTech Connect

    PEARTON,S.J.; REN,F.; ZHANG,A.P.; DANG,G.; CAO,X.A.; LEE,K.P.; CHO,H.; GILA,B.P.; JOHNSON,J.W.; MONIER,C.; ABERNATHY,C.R.; HAN,JUNG; BACA,ALBERT G.; CHYI,J.-I.; LEE,C.-M.; NEE,T.-E.; CHUO,C.-C.; CHU,S.N.G.

    2000-06-12

    A brief review is given of recent progress in fabrication of high voltage GaN and AlGaN rectifiers. GaN/AlGaN heterojunction bipolar transistors and GaN metal-oxide semiconductor field effect transistors. Improvements in epitaxial layer quality and in fabrication techniques have led to significant advances in device performance.

  11. Apollo 1 Prime Crew

    NASA Technical Reports Server (NTRS)

    1966-01-01

    Portrait of the Apollo 1 prime crew for first manned Apollo space flight. From left to right are: Edward H. White II, Virgil I. 'Gus' Grissom, and Roger B. Chaffee. On January 27, 1967 at 5:31 p.m. CST (6:31 local time) during a routine simulated launch test onboard the Apollo Saturn V Moon rocket, an electrical short circuit inside the Apollo Command Module ignited the pure oxygen environment and within a matter of seconds all three Apollo 1 crewmembers perished.

  12. Transposed-Letter Priming Effects with Masked Subset Primes: A Re-Examination of the "Relative Position Priming Constraint"

    ERIC Educational Resources Information Center

    Stinchcombe, Eric J.; Lupker, Stephen J.; Davis, Colin J.

    2012-01-01

    Three experiments are reported investigating the role of letter order in orthographic subset priming (e.g., "grdn"-GARDEN) using both the conventional masked priming technique as well as the sandwich priming technique in a lexical decision task. In all three experiments, subset primes produced priming with the effect being considerably…

  13. Neuroimaging correlates of negative priming.

    PubMed

    Steel, C; Haworth, E J; Peters, E; Hemsley, D R; Sharma, T; Gray, J A; Pickering, A; Gregory, L; Simmons, A; Bullmore, E T; Williams, S C

    2001-11-16

    Many theoretical accounts of selective attention and memory retrieval include reference to active inhibitory processes, such as those argued to underlie the negative priming effect. fMRI was used in order to investigate the areas of cortical activation associated with Stroop interference, Stroop facilitation and Stroop negative priming tasks. The most significant activation within the negative priming task was within the inferior parietal lobule, left temporal lobe and frontal lobes. Areas of cortical activation are discussed with reference to theoretical accounts of the negative priming effect.

  14. Prime mover progress

    SciTech Connect

    Hennagir, T.

    1995-05-01

    Manufacturers continue to upgrade fluidized bed and steam technologies to meet more stringent emission, efficiency and service challenges from global power market customers. Offshore, suppliers are being pushed to provide quality, low-cost production and significant local competitive presence in nearly all international markets. The ability to meet customer and regulatory demands for emissions across different global market segments remains a priority for prime mover suppliers as they develop environmental technical improvements. Products initially developed for the more stringent European regulations are now finding a market in the US. In developing countries, demand continues for utility-size boiler products, but pollution control equipment costs remain a parallel consideration. Industry improvements to steam cycle equipment, namely turbines, continue to reap benefits in terms of efficiency and operational flexibility. Boiler and steam manufacturers` response to global markets remains right on target as product development strategies are constantly adjusted and analyzed to reach an optimum marketing mix. Innovation and advances in prime mover power equipment technology remain a mainstay of suppliers` ability to meet the needs of a changing, competitive clientele.

  15. GaN: Defect and Device Issues

    SciTech Connect

    Pearton, S.J.; Ren, F.; Shul, R.J.; Zolper, J.C.

    1998-11-09

    The role of extended and point defects, and key impurities such as C, O and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

  16. Yellow Luminescence Centers of GaN

    NASA Astrophysics Data System (ADS)

    Zhao, Guangyuan; Hubbard, Seth; Pavlidis, Dimitris

    2004-05-01

    The method for measuring Shockley-Read-Hall (SRH) lifetime of yellow centers of GaN was developed. The capture-section ratio (150) of hole to electron is extracted by comparing the experimental and theoretical results. A marked increase in the SRH lifetime (from 0.75 to 7.0 ns) with the increasing in Si doping density (from 1.5× 1017 to 8.8× 1018 cm-3) was observed, and it is attributed to some Si dopant substituting for the Ga vacancy. In addition, it is also found that the YL centers are an important factor limiting the performance of GaN-based devices.

  17. 5[prime] to 3[prime] nucleic acid synthesis using 3[prime]-photoremovable protecting group

    DOEpatents

    Pirrung, M.C.; Shuey, S.W.; Bradley, J.C.

    1999-06-01

    The present invention relates, in general, to a method of synthesizing a nucleic acid, and, in particular, to a method of effecting 5[prime] to 3[prime] nucleic acid synthesis. The method can be used to prepare arrays of oligomers bound to a support via their 5[prime] end. The invention also relates to a method of effecting mutation analysis using such arrays. The invention further relates to compounds and compositions suitable for use in such methods.

  18. Investigating Home Primes and Their Families

    ERIC Educational Resources Information Center

    Herman, Marlena; Schiffman, Jay

    2014-01-01

    The process of prime factor splicing to generate home primes raises opportunity for conjecture and exploration. The notion of "home primes" is relatively new in the chronicle of mathematics. Heleen (1996-97) first described a procedure called "prime factor splicing" (PFS). The exploration of home primes is interesting and…

  19. Attention to primes modulates affective priming of pronunciation responses.

    PubMed

    De Houwer, Jan; Randell, Tom

    2002-01-01

    In studies on affective priming of pronunciation responses, two words are presented on each trial and participants are asked to read the second word out loud. Whereas some studies revealed shorter reaction times when the two words had the same valence than when they had a different valence, other studies either found no effect of affective congruence or revealed a reversed effect. In the present experiments, a significant effect of affective congruence only emerged when filler trials were presented in which the prime and target were identical and participants were instructed to attend to the primes (Experiment 2). No effects were found when participants were merely instructed to attend to or ignore the primes (Experiment 1), or when affectively incongruent filler trials were presented and participants were instructed to ignore the primes (Experiment 2).

  20. The Near-Earth Encounter of 2005 YU55: Thermal Infrared Observations from Gemini North

    NASA Technical Reports Server (NTRS)

    Lim, Lucy F.; Emery, Joshua P.; Moskovitz, Nicholas A.; Granvik, Mikael

    2012-01-01

    As part of a multi-observatory campaign to observe 2005 YU55 during its November 2011 encounter with the Earth, thermal infrared photometry and spectroscopy (7.9- 14 and 18-22 micron) were conducted using the Michelle instrument at Gemini North. Reduction of the 8.8 flm photometry and the spectroscopy from UT Nov-IO as well as of all the Gemini data from UT Nov-9 is in progress. Results will be discussed.

  1. Call for Lightcurves: Fast Flyby of Near-Earth Asteroid 2005 YU55

    NASA Astrophysics Data System (ADS)

    Moskovitz, Nicholas; Warner, Brian D.

    2011-10-01

    As noted in the Photometry Opportunities article (this issue), on November 8, 2011 at 23:28 UT the approximately 400-meter Ctype asteroid 2005 YU55 will pass inside the Moonís orbit at 0.0022 AU (85% of the Earth-Moon distance) and reach a brightness of V~11. Such an encounter for an asteroid of this size occurs but once every few decades and thus enables a host of exciting and novel scientific investigations.

  2. Cathodoluminescence characterization of suspended GaN nanomembranes

    NASA Astrophysics Data System (ADS)

    Stevens-Kalceff, M. A.; Tiginyanu, I. M.; Popa, V.; Braniste, T.; Brenner, P.

    2013-07-01

    Continuous suspended ˜15 nm thick gallium nitride (GaN) nano-membranes have been investigated using cathodoluminescence microanalysis. The GaN nanomembranes are fabricated by focused ion beam (FIB) pre-treatment of GaN epilayer surfaces followed by photoelectrochemical (PEC) etching. CL microanalysis enables high sensitivity, nanoscale spatial resolution detection of impurities, and defects, and is associated with key features of the suspended GaN nano-membranes. CL spectra and images of the suspended nano-membranes reveal the broad emission band at ˜2.2 eV which is associated with deep acceptor states and the near edge emission at ˜3.4 eV which is associated with free exciton transitions at 295 K. The near edge emission can be resolved into two components, one associated with emission from the nanomembrane and the other associated with CL from underlying GaN transmitted through the nanomembrane. CL spectroscopy gives insight into the physical properties and optical quality of the suspended GaN nano-membranes. Blue shift of the CL near band edge emission indicates that the suspended GaN nanomembranes exhibit the combined effects of quantum confinement and strain.

  3. GaN power devices for automotive applications

    NASA Astrophysics Data System (ADS)

    Uesugi, T.; Kachi, Tetsu

    2013-03-01

    GaN is an attractive material for high performance power devices. Vertical GaN power devices are suitable for high current operation, on the other hand, lateral GaN power devices, namely GaN lateral HEMTs have both low on-resistance and low parasitic capacitance. In addition, the GaN lateral HEMTs can be fabricated on Si substrate. We can get low conduction loss and low switching loss devices with low cost. So the GaN lateral HEMTs are suitable for subsystems like an air conditioner and an electric power steering. Serious technical issues about GaN power devices are a normally-off operation, a current collapse, and a high quality gate insulator. Several normally-off operation techniques have been proposed but there is no decisive method. An NH3 surface treatment and a SiO2 passivation are useful to suppress the current collapse. An Al2O3 deposited by ALD is excellent for gate insulator in breakdown and it has enough TDDB reliability under room temperature and 150°C.

  4. The Near-Earth Encounter of Asteroid 308635 (2005 YU55): Thermal IR Observations

    NASA Technical Reports Server (NTRS)

    Lim, Lucy F.; Emery, J. P.; Moskovitz, N. A.; Busch, N. W.; Yang, B.; Granvik, M.

    2012-01-01

    The near-Earth approach (0.00217 AU, or 0.845 lunar distances) of the C-type asteroid 308635 (2005 YU55) in November 2011 presented a rare opportunity for detailed observations of a low-albedo NEA in this size range. As part of a multi-telescope campaign to measure visible and infrared spectra and photometry, we obtained mid-infrared (approx. 8 to 22 micron) photometry and spectroscopy of 2005 YU55 using Michelle on the Gemini North telescope on UT November 9 and 10,2011. An extensive radar campaign together with optical light-curves established the rotation state of YU55. In addition, the radar imaging resulted in a shape model for the asteroid, detection of numerous boulders on its surface, and a preliminary estimate of its equatorial diameter at 380 +/- 20 m. In a preliminary analysis, applying the radar and lightcurve-derived parameters to a rough-surface thermophysical model fit to the Gemini/Michelle thermal emission photometry results in a thermal inertia range of approximately 500 to 1500 J/sq m/0.5s/K, with the low-thermal-inertia solution corresponding to the small end of the radar size range and vice versa. Updates to these results will be presented and modeling of the thermal contribution to the measured near-infrared spectra from Palomar/Triplespec and IRTF/SpeX will also be discussed.

  5. Representing Numbers: Prime and Irrational

    ERIC Educational Resources Information Center

    Zazkis, Rina

    2005-01-01

    This article draws an analogy between prime and irrational numbers with respect to how these numbers are defined and how they are perceived by learners. Excerpts are presented from two research studies: a study on understanding prime numbers by pre-service elementary school teachers and a study on understanding irrational numbers by pre-service…

  6. Priming Macho Attitudes and Emotions.

    ERIC Educational Resources Information Center

    Beaver, Erik D.; And Others

    1992-01-01

    Investigated the effects of reading one of four priming stimuli stories (control, consenting sex, rape, or family) on males' evaluations of, and emotional reactions to, two videotaped date-rape scenarios. Results supported the concepts of a macho personality and revealed interactive effects for both the rape and family prime. (RJM)

  7. Exodus: Prime Mover

    NASA Technical Reports Server (NTRS)

    Bauer, Nikkol; Conwell, Pete; Johnson, Matt; Shields, Wendy; Thornton, Tim; Tokarz, Rob; Mcmanus, Rich

    1992-01-01

    The Exodus Prime Mover is an overnight package delivery aircraft designed to serve the Northern Hemisphere of Aeroworld. The preliminary design goals originated from the desire to produce a large profit. The two main driving forces throughout the design process were first to reduce the construction man-hours by simplifying the aircraft design, thereby decreasing the total production cost of the aircraft. The second influential factor affecting the design was minimizing the fuel cost during cruise. The lowest fuel consumption occurs at a cruise velocity of 30 ft/s. Overall, it was necessary to balance the economic benefits with the performance characteristics in order to create a profitable product that meets all specified requirements and objectives.

  8. GaN for LED applications

    NASA Technical Reports Server (NTRS)

    Pankove, J. I.

    1973-01-01

    In order to improve the synthesis of GaN the effect of various growth and doping parameters has been studied. Although Be, Li, Mg, and Dy can be used to overcompensate native donors, the most interesting acceptor element is Zn. The emission spectrum and the luminescence efficiency depend on the growth temperature (below 800 C), on the partial pressure of the doping impurity, and on the duration of growth. Blue-green electroluminescence with a power efficiency of 0.1 percent and a brightness of 850 fL (at 0.6 mA and 22.5 V) was obtained. Some diodes allow the color of the emitted light to change by reversing the polarity of the bias. Continuous operation of a diode over a period of 5 months showed no evidence of degradation. The luminescence properties of ion-implanted GaN were studied. Delay effects were found in the electroluminescence of diodes, although, with a dc bias, a 70-MHz modulation was possible.

  9. Development of GaN photocathodes for UV detectors

    NASA Astrophysics Data System (ADS)

    Siegmund, O.; Vallerga, J.; McPhate, J.; Malloy, J.; Tremsin, A.; Martin, A.; Ulmer, M.; Wessels, B.

    2006-11-01

    We have made substantial progress in the development of GaN photocathodes, including crystalline and polycrystalline GaN and InGaN coatings grown by chemical vapor deposition or molecular beam epitaxy on sapphire substrates. GaN and InGaN photocathodes have been developed with efficiencies up to 70% and cutoffs at ˜380 nm with low out of band response, and high stability and longevity. Samples have been processed and tested at ultra high vacuum to establish cathode process parameters, and some have been integrated into sealed tubes for long-term evaluation.

  10. Optical spectroscopy of cubic GaN in nanowires

    NASA Astrophysics Data System (ADS)

    Renard, J.; Tourbot, G.; Sam-Giao, D.; Bougerol, C.; Daudin, B.; Gayral, B.

    2010-08-01

    We show that highly homogeneous cubic GaN can be grown by plasma-assisted molecular beam epitaxy on wurtzite GaN nanowires. The line width of the donor bound exciton is below 3 meV and can reach 1.6 meV in the best parts of the studied sample. This allows to perform a detailed spectroscopy of cubic GaN, and, in particular, to determine the precise spectral positions of the donor bound exciton, the fundamental free exciton and the split-off exciton in a photoluminescence experiment.

  11. Crystallography and elasticity of individual GaN nanotubes

    NASA Astrophysics Data System (ADS)

    Liu, Baodan; Bando, Yoshio; Wang, Mingsheng; Tang, Chengchun; Mitome, Masanori; Golberg, Dmitri

    2009-05-01

    High-purity, crystalline [001]-oriented GaN nanotubes with outer diameters of 200 nm or more, rough surfaces and irregular internal channels were synthesized under epitaxial growth on [001]-oriented sapphire substrates. Elastic property measurements on free-standing individual GaN nanotubes, using the in situ transmission electron microscopy (TEM) electromechanical resonance technique, pointed at an average Young's modulus E of 37 GPa and minimum quality factor of 320. These numbers are notably lower than those for previously reported GaN nanowires. The crystallography and chemistry of the GaN nanotubes were analyzed using TEM and energy dispersion x-ray spectroscopy (EDS). It is suggested that the lowered Young's modulus and quality factor of the nanotubes are mainly due to the surface roughness and defectiveness.

  12. Novel high frequency devices with graphene and GaN

    NASA Astrophysics Data System (ADS)

    Zhao, Pei

    This work focuses on exploring new materials and new device structures to develop novel devices that can operate at very high speed. In chapter 2, the high frequency performance limitations of graphene transistor with channel length less than 100 nm are explored. The simulated results predict that intrinsic cutoff frequency fT of graphene transistor can be close to 2 THz at 15 nm channel length. In chapter 3, we explored the possibility of developing a 2D materials based vertical tunneling device. An analytical model to calculate the channel potentials and current-voltage characteristics in a Symmetric tunneling Field-Effect-Transistor (SymFET) is presented. The symmetric resonant peak in SymFET is a good candidate for high-speed analog applications. Rest of the work focuses on Gallium Nitride (GaN), several novel device concepts based on GaN heterostructure have been proposed for high frequency and high power applications. In chapter 4, we compared the performance of GaN Schottky diodes on bulk GaN substrates and GaN-on-sapphire substrates. In addition, we also discussed the lateral GaN Schottky diode between metal/2DEGs. The advantage of lateral GaN Schottky diodes is the intrinsic cutoff frequency is in the THz range. In chapter 5, a GaN Heterostructure barrier diode (HBD) is designed using the polarization charge and band offset at the AlGaN/GaN heterojunction. The polarization charge at AlGaN/GaN interface behaves as a delta-doping which induces a barrier without any chemical doping. The IV characteristics can be explained by the barrier controlled thermionic emission current. GaN HBDs can be directly integrated with GaN HEMTs, and serve as frequency multipliers or mixers for RF applications. In chapter 6, a GaN based negative effective mass oscillator (NEMO) is proposed. The current in NEMO is estimated under the ballistic limits. Negative differential resistances (NDRs) can be observed with more than 50% of the injected electrons occupied the negative

  13. GaN nanorods coated with pure BN

    NASA Astrophysics Data System (ADS)

    Han, Wei-Qiang; Zettl, A.

    2002-12-01

    We report a method to efficiently synthesize gallium nitride (GaN) nanorods coated with insulating boron nitride (BN) layers. The GaN core is crystalline (with either a cubic zincblende or hexagonal wurtzite structure) and has diameters ranging from 10 to 85 nm and lengths up to 60 μm. The outer encapsulating BN shells with typical thicknesses less than 5 nm extend fully over, and adhere well to, the entire nanorod surface.

  14. Terahertz response of GaN thin films.

    PubMed

    Tsai, Tsong-Ru; Chen, Shi-Jie; Chang, Chih-Fu; Hsu, Sheng-Hsien; Lin, Tai-Yuan; Chi, Cheng-Chung

    2006-05-29

    The indices of refraction, extinction constants and complex conductivities of the GaN film for frequencies ranging from 0.2 to 2.5 THz are obtained using THz time-domain spectroscopy. The results correspond well with the Kohlrausch stretched exponential model. Using the Kohlrausch model fit not only provides the mobility of the free carriers in the GaN film, but also estimates the relaxation time distribution function and average relaxation time.

  15. ARM MJO Investigation Experiment on Gan Island (AMIE-Gan) Science Plan

    SciTech Connect

    Long, CL; Del Genio, A; Deng, M; Fu, X; Gustafson, W; Houze, R; Jakob, C; Jensen, M; Johnson, R; Liu, X; Luke, E; May, P; McFarlane, S; Minnis, P; Schumacher, C; Vogelmann, A; Wang, Y; Webster, P; Xie, S; Zhang, C

    2011-04-11

    The overarching campaign, which includes the ARM Mobile Facility 2 (AMF2) deployment in conjunction with the Dynamics of the Madden-Julian Oscillation (DYNAMO) and the Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011) campaigns, is designed to test several current hypotheses regarding the mechanisms responsible for Madden-Julian Oscillation (MJO) initiation and propagation in the Indian Ocean area. The synergy between the proposed AMF2 deployment with DYNAMO/CINDY2011, and the corresponding funded experiment on Manus, combine for an overarching ARM MJO Investigation Experiment (AMIE) with two components: AMF2 on Gan Island in the Indian Ocean (AMIE-Gan), where the MJO initiates and starts its eastward propagation; and the ARM Manus site (AMIE-Manus), which is in the general area where the MJO usually starts to weaken in climate models. AMIE-Gan will provide measurements of particular interest to Atmospheric System Research (ASR) researchers relevant to improving the representation of MJO initiation in climate models. The framework of DYNAMO/CINDY2011 includes two proposed island-based sites and two ship-based locations forming a square pattern with sonde profiles and scanning precipitation and cloud radars at both island and ship sites. These data will be used to produce a Variational Analysis data set coinciding with the one produced for AMIE-Manus. The synergy between AMIE-Manus and AMIE-Gan will allow studies of the initiation, propagation, and evolution of the convective cloud population within the framework of the MJO. As with AMIE-Manus, AMIE-Gan/DYNAMO also includes a significant modeling component geared toward improving the representation of MJO initiation and propagation in climate and forecast models. This campaign involves the deployment of the second, marine-capable, AMF; all of the included measurement systems; and especially the scanning and vertically pointing radars. The campaign will include sonde

  16. Space Place Prime

    NASA Technical Reports Server (NTRS)

    Fitzpatrick, Austin J.; Novati, Alexander; Fisher, Diane K.; Leon, Nancy J.; Netting, Ruth

    2013-01-01

    Space Place Prime is public engagement and education software for use on iPad. It targets a multi-generational audience with news, images, videos, and educational articles from the Space Place Web site and other NASA sources. New content is downloaded daily (or whenever the user accesses the app) via the wireless connection. In addition to the Space Place Web site, several NASA RSS feeds are tapped to provide new content. Content is retained for the previous several days, or some number of editions of each feed. All content is controlled on the server side, so features about the latest news, or changes to any content, can be made without updating the app in the Apple Store. It gathers many popular NASA features into one app. The interface is a boundless, slidable- in-any-direction grid of images, unique for each feature, and iconized as image, video, or article. A tap opens the feature. An alternate list mode presents menus of images, videos, and articles separately. Favorites can be tagged for permanent archive. Face - book, Twitter, and e-mail connections make any feature shareable.

  17. Fabrication and properties of nanoporous GaN films

    NASA Astrophysics Data System (ADS)

    Wang, Y. D.; Chua, S. J.; Sander, M. S.; Chen, P.; Tripathy, S.; Fonstad, C. G.

    2004-08-01

    Nanopore arrays with pore diameters of approximately 75nm were fabricated in GaN films by inductively coupled plasma etching using anodic aluminum oxide (AAO) films as etch masks. Nanoporous AAO films were formed on the GaN surface by evaporating an Al film onto a GaN epilayer and subsequently anodizing the aluminum. To minimize plasma-induced damage, the template was exposed to CF4-based plasma conditions. Scanning electron microscopy analysis shows that the diameter and the periodicity of the nanopores in the GaN were directly transferred from the original anodic alumina template. The pore diameter in the AAO film can be easily controlled by tuning the anodization conditions. Atomic force microscopy, photoluminescence, and micro-Raman techniques were employed to assess the etched GaN nanopore surface. This cost-effective, nonlithographic method to produce nano-patterned GaN templates is expected to be useful for growth and fabrication of nitride-based nanostructures and photonic band gap materials.

  18. High nitrogen pressure solution growth of GaN

    NASA Astrophysics Data System (ADS)

    Bockowski, Michal

    2014-10-01

    Results of GaN growth from gallium solution under high nitrogen pressure are presented. Basic of the high nitrogen pressure solution (HNPS) growth method is described. A new approach of seeded growth, multi-feed seed (MFS) configuration, is demonstrated. The use of two kinds of seeds: free-standing hydride vapor phase epitaxy GaN (HVPE-GaN) obtained from metal organic chemical vapor deposition (MOCVD)-GaN/sapphire templates and free-standing HVPE-GaN obtained from the ammonothermally grown GaN crystals, is shown. Depending on the seeds’ structural quality, the differences in the structural properties of pressure grown material are demonstrated and analyzed. The role and influence of impurities, like oxygen and magnesium, on GaN crystals grown from gallium solution in the MFS configuration is presented. The properties of differently doped GaN crystals are discussed. An application of the pressure grown GaN crystals as substrates for electronic and optoelectronic devices is reported.

  19. The PRIME Lab biomedical program

    NASA Astrophysics Data System (ADS)

    Jackson, George S.; Elmore, David; Rickey, Frank A.; Musameh, Sharif M.; Sharma, Pankaj; Hillegonds, Darren; Coury, Louis; Kissinger, Peter

    2000-10-01

    The biomedical accelerator mass spectrometry (AMS) initiative at PRIME Lab including the status of equipment and sample preparation is described. Several biomedical projects are underway involving one or more of the nuclides: 14C, 26Al and 41Ca. Routine production of CaF 2 and graphite is taking place. Finally, the future direction and plans for improvement of the biomedical program at PRIME Lab are discussed.

  20. MIL-PRIME Program System

    NASA Astrophysics Data System (ADS)

    Rall, F. T., Jr.

    1982-11-01

    The MIL-PRIME Program was developed to provide the Aeronautical Systems Division with a specifications and standards program for the development of new weapon systems. This program was started in 1976 and is still in the process of being implemented. This presentation provides the background and insight into the MIL PRIME System, the use of these new documents in the acquisition process, and the current status of the program.

  1. Role of the ganSPQAB Operon in Degradation of Galactan by Bacillus subtilis.

    PubMed

    Watzlawick, Hildegard; Morabbi Heravi, Kambiz; Altenbuchner, Josef

    2016-10-15

    Bacillus subtilis possesses different enzymes for the utilization of plant cell wall polysaccharides. This includes a gene cluster containing galactan degradation genes (ganA and ganB), two transporter component genes (ganQ and ganP), and the sugar-binding lipoprotein-encoding gene ganS (previously known as cycB). These genes form an operon that is regulated by GanR. The degradation of galactan by B. subtilis begins with the activity of extracellular GanB. GanB is an endo-β-1,4-galactanase and is a member of glycoside hydrolase (GH) family 53. This enzyme was active on high-molecular-weight arabinose-free galactan and mainly produced galactotetraose as well as galactotriose and galactobiose. These galacto-oligosaccharides may enter the cell via the GanQP transmembrane proteins of the galactan ABC transporter. The specificity of the galactan ABC transporter depends on the sugar-binding lipoprotein, GanS. Purified GanS was shown to bind galactotetraose and galactotriose using thermal shift assay. The energy for this transport is provided by MsmX, an ATP-binding protein. The transported galacto-oligosaccharides are further degraded by GanA. GanA is a β-galactosidase that belongs to GH family 42. The GanA enzyme was able to hydrolyze short-chain β-1,4-galacto-oligosaccharides as well as synthetic β-galactopyranosides into galactose. Thermal shift assay as well as electrophoretic mobility shift assay demonstrated that galactobiose is the inducer of the galactan operon regulated by GanR. DNase I footprinting revealed that the GanR protein binds to an operator overlapping the -35 box of the σ(A)-type promoter of Pgan, which is located upstream of ganS IMPORTANCE: Bacillus subtilis is a Gram-positive soil bacterium that utilizes different types of carbohydrates, such as pectin, as carbon sources. So far, most of the pectin degradation systems and enzymes have been thoroughly studied in B. subtilis Nevertheless, the B. subtilis utilization system of galactan, which is

  2. The pharmacology of nociceptor priming.

    PubMed

    Kandasamy, Ram; Price, Theodore J

    2015-01-01

    Nociceptors and neurons in the central nervous system (CNS) that receive nociceptive input show remarkable plasticity in response to injury. This plasticity is thought to underlie the development of chronic pain states. Hence, further understanding of the molecular mechanisms driving and maintaining this plasticity has the potential to lead to novel therapeutic approaches for the treatment of chronic pain states. An important concept in pain plasticity is the presence and persistence of "hyperalgesic priming." This priming arises from an initial injury and results in a remarkable susceptibility to normally subthreshold noxious inputs causing a prolonged pain state in primed animals. Here we describe our current understanding of how this priming is manifested through changes in signaling in the primary nociceptor as well as through memory like alterations at CNS synapses. Moreover, we discuss how commonly utilized analgesics, such as opioids, enhance priming therefore potentially contributing to the development of persistent pain states. Finally we highlight where these priming models draw parallels to common human chronic pain conditions. Collectively, these advances in our understanding of pain plasticity reveal a variety of targets for therapeutic intervention with the potential to reverse rather than palliate chronic pain states.

  3. Psychotherapy Augmentation through Preconscious Priming

    PubMed Central

    Borgeat, François; O’Connor, Kieron; Amado, Danielle; St-Pierre-Delorme, Marie-Ève

    2013-01-01

    Objective: To test the hypothesis that repeated preconscious (masked) priming of personalized positive cognitions could augment cognitive change and facilitate achievement of patients’ goals following a therapy. Methods: Twenty social phobic patients (13 women) completed a 36-weeks study beginning by 12 weeks of group behavioral therapy. After the therapy, they received 6 weeks of preconscious priming and 6 weeks of a control procedure in a randomized cross-over design. The Priming condition involved listening twice daily with a passive attitude to a recording of individualized formulations of appropriate cognitions and attitudes masked by music. The Control condition involved listening to an indistinguishable recording where the formulations had been replaced by random numbers. Changes in social cognitions were measured by the Social Interaction Self Statements Test (SISST). Results: Patients improved following therapy. The Priming procedure was associated with increased positive cognitions and decreased negative cognitions on the SISST while the Control procedure was not. The Priming procedure induced more cognitive change when applied immediately after the group therapy. Conclusion: An effect of priming was observed on social phobia related cognitions in the expected direction. This self administered addition to a therapy could be seen as an augmentation strategy. PMID:23508724

  4. The Pharmacology of Nociceptor Priming

    PubMed Central

    Kandasamy, Ram

    2015-01-01

    Nociceptors and neurons in the central nervous system (CNS) that receive nociceptive input show remarkable plasticity in response to injury. This plasticity is thought to underlie the development of chronic pain states. Hence, further understanding of the molecular mechanisms driving and maintaining this plasticity has the potential to lead to novel therapeutic approaches for the treatment of chronic pain states. An important concept in pain plasticity is the presence and persistence of “hyperalgesic priming.” This priming arises from an initial injury and results in a remarkable susceptibility to normally subthreshold noxious inputs causing a prolonged pain state in primed animals. Here we describe our current understanding of how this priming is manifested through changes in signaling in the primary nociceptor as well as through memory like alterations at CNS synapses. Moreover, we discuss how commonly utilized analgesics, such as opioids, enhance priming therefore potentially contributing to the development of persistent pain states. Finally we highlight where these priming models draw parallels to common human chronic pain conditions. Collectively, these advances in our understanding of pain plasticity reveal a variety of targets for therapeutic intervention with the potential to reverse rather than palliate chronic pain states. PMID:25846612

  5. Growth and development of permanent teeth germ of transplacental Yu-Cheng babies in Taiwan

    SciTech Connect

    Lan, Shoujen; Yen, Yeayin; Ko, Yingchin; Chen, Engrin )

    1989-06-01

    This paper is intended to present a study of transplacental Yu-Cheng babies in Taiwan. The focus of the study is to demonstrate how a contaminated food source can affect the growth and development of permanent teeth germ in children. A sporadic outbreak of a peculiar skin disease was reported in Japan in October of 1968. An epidemiological study revealed the outbreak of this disease was caused by contaminated Kanemi rice oil. This episode of rice oil poisoned with polychlorinated biphenyls (PCB) was the first reported outbreak of PCB poisoning in the world. A second episode occurred in central Taiwan eleven years after the Japanese episode. Registered data from the Taiwan Provincial Government Health Department reported 1,843 cases in 1980. Of this group, more than 800 women were child-bearing age and most of these women would or soon would be married and pregnant. The offsprings of these women were in danger, because it has been proven that PCB intoxication could affect the fetus. These babies, only contaminated through the placenta, are called PCB transplacental Yusho babies in Japan and PCB transplacental Yu-Cheng babies in Taiwan. Babies with PCB poisoning could have Fetal PCB syndrome (FPS) and may have retarded eruption of permanent teeth and other anomalies such as reduced numbers of teeth and abnormal shaped roots. The study of transplacental Yu-Cheng babies is an important public health issue for Taiwan. Although there may be other issues, this study focuses only on the growth and development of permanent teeth of those babies affected by PCB transplacental contamination.

  6. Growth of freestanding GaN using pillar-epitaxial lateral overgrowth from GaN nanocolumns

    NASA Astrophysics Data System (ADS)

    Bougrioua, Z.; Gibart, P.; Calleja, E.; Jahn, U.; Trampert, A.; Ristic, J.; Utrera, M.; Nataf, G.

    2007-12-01

    Dislocation-free and strain-free GaN nanopillars, grown on Si by molecular beam epitaxy, were used as nanoseeds for a new form of epitaxial lateral overgrowth (ELO) by metalorganic vapour phase epitaxy (MOVPE) until full coalescence. Such overgrown GaN films are almost relaxed and were used as templates for producing thick GaN layers by halide vapour phase epitaxy (HVPE). The final GaN film is easily separated from the starting Si substrate. This is henceforth a new technology to produce freestanding GaN. The GaN crystal quality was assessed by transmission electron microscopy (TEM), photo- and cathodoluminescence (PL, CL). It was seen that the pillar-ELO is produced from a limited number of nanopillars. Some dislocations and basal stacking faults are formed during the coalescence. However, those that propagate parallel to the substrate do not replicate in the top layer and it is expected that the thickened material present a reduced defect density.

  7. DLTS study of n-type GaN grown by MOCVD on GaN substrates

    NASA Astrophysics Data System (ADS)

    Tokuda, Y.; Matsuoka, Y.; Ueda, H.; Ishiguro, O.; Soejima, N.; Kachi, T.

    2006-10-01

    Electron traps in n-type GaN layers grown homoepitaxially by MOCVD on free-standing GaN substrates have been characterized using DLTS for vertical Schottky diodes. Two free-standing HVPE GaN substrates (A and B), obtained from two different sources, are used. The Si-doped GaN layers with the thickness of 5 μm are grown on an area of 0.9×0.9 cm 2 of substrate A and on an area of 1×1 cm 2 of substrate B. Two traps labeled B1 (Ec-0.23 eV) and B2 (Ec-0.58 eV) are observed with trap B2 dominant in GaN on both substrates. There exist no dislocation-related traps which have been previously observed in MOCVD GaN on sapphire. This might be correlated to the reduction in dislocation density due to the homoepitaxial growth. However, it is found that there is a large variation, more than an order of magnitude, in trap B2 concentration and that the B2 spatial distributions are different between the two substrates used.

  8. Test Sequence Priming in Recognition Memory

    ERIC Educational Resources Information Center

    Johns, Elizabeth E.; Mewhort, D. J. K.

    2009-01-01

    The authors examined priming within the test sequence in 3 recognition memory experiments. A probe primed its successor whenever both probes shared a feature with the same studied item ("interjacent priming"), indicating that the study item like the probe is central to the decision. Interjacent priming occurred even when the 2 probes did…

  9. [Textual research on Guang dong xin yu (New Sayings of Guangdong) quoted in Ben cao gang mu shi yi (Supplements to Compendium of Materia Medica].

    PubMed

    Zhang, Ruixian; Zhang, Wei; Li, Jian; Liang, Fei

    2014-05-01

    Altogether 15 terms for Guang dong xin yu (New Sayings of Guangdong) were used in Ben cao gang mu shi yi (Supplements to Compendium of Materia Medica), including Yue yu (Cantonese sayings), Chong yu (Sayings from Insect Drug), Jie yu (Sayings from Crustacean Drug), Xin yu (New Sayings), Yue hai xiang yu (Fragrant Sayings from Cantonese Region), Yue zhi mu yu (Sayings from Plants in Cantonese Annals), Guang dong suo yu (Trivial Sayings from Guangdong), Yue shan lu (Records of Cantonese Mountains), Yue lu (Cantonese Records), Jiao guang lu (Joint Guangdong Records), Yue cao zhi (Records of Cantonese Grasses), Guang guo lu (Records of Guangdong Fruits), Nan yue suo ji (Trivial Records of Southern Canton), Guang zhi (Guangdong Records), Yue zhi (Cantonese Records) etc. dealing with 57 sorts of drugs (with individual overlapping ones), the author of Xin yu was Qu Dajun, a surviving fogy of the Ming Dynasty actively involved in the activities to restore the old dynasty and resist the Qing Dynasty, and was persecuted in the literary inquisition in which his works were burnt so that Zhao Xuemin, when quoting his texts, had to go in a roundabout way.

  10. Locus of single-prime negative priming: the role of perceptual form.

    PubMed

    Chao, Hsuan-Fu

    2013-07-01

    Single-prime negative priming refers to the phenomenon in which after a single prime word is briefly presented, repeating it as the probe target results in a delay in responding to the target. The present study investigated the locus of this negative priming effect. Experiment 1 showed that repeating the identity of the prime produced a negative priming effect but merely repeating the response of the prime did not. Experiment 2 showed that the negative priming effect transformed into positive priming when the probe distractor was absent. Experiments 3 and 4 further revealed that single-prime negative priming was observed when the perceptual form was repeated. Taken together, these results suggest that single-prime negative priming involves a perceptual locus.

  11. On the Control of Single-Prime Negative Priming: The Effects of Practice and Time Course

    ERIC Educational Resources Information Center

    Chao, Hsuan-Fu

    2009-01-01

    Single-prime negative priming refers to the phenomenon wherein repetition of a prime as the probe target results in delayed response. Sometimes this effect has been found to be contingent on participants' unawareness of the primes, and sometimes it has not. Further, sometimes this effect has been found to be eliminated when the prime could predict…

  12. The Intervenor Effect in Masked Priming: How Does Masked Priming Survive across an Intervening Word?

    ERIC Educational Resources Information Center

    Forster, Kenneth I.

    2009-01-01

    Four masked priming experiments are reported investigating the effect of inserting an unrelated word between the masked prime and the target. When the intervening word is visible, identity priming is reduced to the level of one-letter-different form priming, but form priming is largely unaffected. However, when the intervening word is itself…

  13. Spectroscopic measurements of the surface stoichiometry of chemical vapor deposited GaN

    NASA Astrophysics Data System (ADS)

    Craft, H. S.; Rice, A. L.; Collazo, R.; Sitar, Z.; Maria, J.-P.

    2011-02-01

    We report on the surface stoichiometry of Ga-polar GaN films grown by metalorganic chemical vapor deposition as studied by x-ray photoelectron spectroscopy. GaN film surfaces are found to be Ga-rich, with Ga:N ratios ranging from 1.3:1 to 3.2:1. In vacuo ion-beam sputter/annealing studies show that these treatments drive the apparent Ga:N surface composition farther from unity, either through a decrease in surface contamination, oxidation of the surface, or both. Simple annealing experiments decrease the Ga:N ratio. The measured GaN ratio is correlated with the GaN growth time, suggesting that residual Ga precursor after growth interacts with the GaN surface as it cools.

  14. Mechanisms of secondary convection within a Mei-Yu frontal mesoscale convective system in eastern China

    NASA Astrophysics Data System (ADS)

    Xu, Xin; Xue, Ming; Wang, Yuan; Huang, Hao

    2017-01-01

    The generation of secondary convection, following an earlier episode of convection, within a heavy-rain-producing mesoscale convective system (MCS) along a Mei-Yu front in eastern China on 6-8 July 2013 is studied based on convection-permitting Weather Research and Forecasting simulations. The initiation of the secondary convection is found to be directly linked to the downward development of a mesoscale convective vortex (MCV) spawn by the MCS. In the early and mature stage, the MCV center is located at the middle troposphere; it descends gradually with time as the parent MCS began to decay, with the associated convection transitioning from deep to shallow convection. The descent of the MCV occurs in response to the lowering of the maximum diabatic heating within the convective system, which increases positive potential vorticity down below. When the MCV reaches the lower troposphere, it becomes coupled with the prefrontal southwesterly low-level jet (LLJ). The confluence of the MCV rotational flow with the LLJ notably enhances the convergence on the southern flank of the MCV, where the secondary convection is triggered and swapped through the southeastern flank of the MCV. Unlike that found in the MCV of the U.S. Central Plains, the cold pool produced by the Mei-Yu frontal MCS is rather weak and shallow and appears to play only a minor role in promoting convection. The balanced isentropic lifting by the MCV circulation is also weak, although the MCV circulation does help localize the secondary convection.

  15. Phenolic component profiles of mustard greens, yu choy, and 15 other brassica vegetables.

    PubMed

    Lin, Long-Ze; Harnly, James M

    2010-06-09

    A liquid chromatography-mass spectrometry (LC-MS) profiling method was used to characterize the phenolic components of 17 leafy vegetables from Brassica species other than Brassica oleracea. The vegetables studied were mustard green, baby mustard green, gai choy, baby gai choy, yu choy, yu choy tip, bok choy, bok choy tip, baby bok choy, bok choy sum, Taiwan bok choy, Shanghai bok choy, baby Shanghai bok choy, rapini broccoli, turnip green, napa, and baby napa. This work led to the tentative identification of 71 phenolic compounds consisting of kaempferol 3-O-diglucoside-7-O-glucoside derivatives, isorhamnetin 3-O-glucoside-7-O-glucoside hydroxycinnamoyl gentiobioses, hydroxycinnamoylmalic acids, and hydroxycinnamoylquinic acids. Ten of the compounds, 3-O-diacyltriglucoside-7-O-glucosides of kaempferol and quercetin, had not been previously reported. The phenolic component profiles of these vegetables were significantly different than those of the leafy vegetables from B. oleracea. This is the first comparative study of these leafy vegetables. Ten of the vegetables had never been previously studied by LC-MS.

  16. Phenolic Component Profiles of Mustard Greens, Yu Choy, and 15 Other Brassica Vegetables

    PubMed Central

    Lin, Long-Ze; Harnly, James M

    2013-01-01

    A liquid chromatography–mass spectrometry (LC-MS) profiling method was used to characterize the phenolic components of 17 leafy vegetables from Brassica species other than Brassica oleracea. The vegetables studied were mustard green, baby mustard green, gai choy, baby gai choy, yu choy, yu choy tip, bok choy, bok choy tip, baby bok choy, bok choy sum, Taiwan bok choy, Shanghai bok choy, baby Shanghai bok choy, rapini broccoli, turnip green, napa, and baby napa. This work led to the tentative identification of 71 phenolic compounds consisting of kaempferol 3-O-diglucoside-7-O-glucoside derivatives, isorhamnetin 3-O-glucoside-7-O-glucoside hydroxycinnamoyl gentiobioses, hydroxycinnamoylmalic acids, and hydroxycinnamoylquinic acids. Ten of the compounds, 3-O-diacyltriglucoside-7-O-glucosides of kaempferol and quercetin, had not been previously reported. The phenolic component profiles of these vegetables were significantly different than those of the leafy vegetables from B. oleracea. This is the first comparative study of these leafy vegetables. Ten of the vegetables had never been previously studied by LC-MS. PMID:20465307

  17. Tailoring GaN semiconductor surfaces with biomolecules.

    PubMed

    Estephan, Elias; Larroque, Christian; Cuisinier, Frédéric J G; Bálint, Zoltán; Gergely, Csilla

    2008-07-24

    Functionalization of semiconductors constitutes a crucial step in using these materials for various electronic, photonic, biomedical, and sensing applications. Within the various possible approaches, selection of material-binding biomolecules from a random biological library, based on the natural recognition of proteins or peptides toward specific material, offers many advantages, most notably biocompatibility. Here we report on the selective functionalization of GaN, an important semiconductor that has found broad uses in the past decade due to its efficient electroluminescence and pronounced chemical stability. A 12-mer peptide ("GaN_probe") with specific recognition for GaN has evolved. The subtle interplay of mostly nonpolar hydrophobic and some polar amino acidic residues defines the high affinity adhesion properties of the peptide. The interaction forces between the peptide and GaN are quantified, and the hydrophobic domain of the GaN_probe is identified as primordial for the binding specificity. These nanosized binding blocks are further used for controlled placement of biotin-streptavidin complexes on the GaN surface. Thus, the controlled grow of a new, patterned inorganic-organic hybrid material is achieved. Tailoring of GaN by biological molecules can lead to a new class of nanostructured semiconductor-based devices.

  18. Native defects in GaN: a hybrid functional study

    NASA Astrophysics Data System (ADS)

    Diallo, Ibrahima Castillo; Demchenko, Denis

    Intrinsic defects play an important role in the performance of GaN-based devices. We present hybrid density functional calculations of the electronic and possible optical properties of interstitial N (Ni-Ni) , N antisite (NGa) , interstitial Ga (Gai) , Ga antisite (GaN) , Ga vacancy (VGa) , N vacancy (VN) and Ga-N divacancies (VGaVN) in GaN. Our results show that the vacancies display relatively low formation energies in certain samples, whereas antisites and interstitials are energetically less favorable. However, interstitials can be created by electron irradiation. For instance, in 2.5 MeV electron-irradiated GaN samples, a strong correlation between the frequently observed photoluminescence (PL) band centered around 0.85 eV accompanied with a rich phonon sideband of ~0.88 eV and the theoretical optical behavior of interstitial Ga is discussed. N vacancies are found to likely contribute to the experimentally obtained green luminescence band (GL2) peaking at 2.24 eV in high-resistivity undoped and Mg-doped GaN. National Science Foundation (DMR-1410125) and the Thomas F. and Kate Miller Jeffress Memorial Trust.

  19. Pulsed laser annealing of Be-implanted GaN

    NASA Astrophysics Data System (ADS)

    Wang, H. T.; Tan, L. S.; Chor, E. F.

    2005-11-01

    Postimplantation thermal processing of Be in molecular-beam-epitaxy-grown GaN by rapid thermal annealing (RTA) and pulsed laser annealing (PLA) was investigated. It has been found that the activation of Be dopants and the repair of implantation-induced defects in GaN films cannot be achieved efficiently by conventional RTA alone. On the other hand, good dopant activation and surface morphology and quality were obtained when the Be-implanted GaN film was annealed by PLA with a 248 nm KrF excimer laser. However, observations of off-resonant micro-Raman and high-resolution x-ray-diffraction spectra indicated that crystal defects and strain resulting from Be implantation were still existent after PLA, which probably degraded the carrier mobility and limited the activation efficiency to some extent. This can be attributed to the shallow penetration depth of the 248 nm laser in GaN, which only repaired the crystal defects in a thin near-surface layer, while the deeper defects were not annealed out well. This situation was significantly improved when the Be-implanted GaN was subjected to a combined process of PLA followed by RTA, which produced good activation of the dopants, good surface morphology, and repaired bulk and surface defects well.

  20. Chemical composition, isotopic U-Pb age, and source of zircon from polymineralic ichet'yu occurrence, Mobile Timan

    NASA Astrophysics Data System (ADS)

    Makeev, A. B.; Bayanova, T. B.; Borisovsky, S. E.; Zhilicheva, O. M.

    2016-12-01

    This study focuses on the morphological features, color cathodoluminescence, chemical composition, age, and source of zircons from the Ichet'yu occurrence. The isotopic U-Pb age of Paleo-Mezoproterozoic zircon grains varies within an interval of 700 Ma from 2247 to 1478 Ma. The average roundness and well-preserved integrity of zircon grains allow us to suggest their proximal source. The available data show that the basement of the Middle Timan, composed of continental Paleo-Mezoproterozoic igneous rocks, is the most probable source of zircon in the Ichet'yu occurrence. These rocks are apparently a continuation of the Archean-Proterozoic Arkhangel'sk Mobile Belt.

  1. The Affective Regulation of Cognitive Priming

    PubMed Central

    Storbeck, Justin; Clore, Gerald L.

    2008-01-01

    Semantic and affective priming are classic effects observed in cognitive and social psychology, respectively. We discovered that affect regulates such priming effects. In Experiment 1, positive and negative moods were induced prior to one of three priming tasks; evaluation, categorization, or lexical decision. As predicted, positive affect led to both affective priming (evaluation task) and semantic priming (category and lexical decision tasks). However, negative affect inhibited such effects. In Experiment 2, participants in their natural affective state completed the same priming tasks as in Experiment 1. As expected, affective priming (evaluation task) and category priming (categorization and lexical decision tasks) were observed in such resting affective states. Hence, we conclude that negative affect inhibits semantic and affective priming. These results support recent theoretical models, which suggest that positive affect promotes associations among strong and weak concepts, and that negative affect impairs such associations (Kuhl, 2000; Clore & Storbeck, 2006). PMID:18410195

  2. Priming and Habituation for Faces: Individual Differences and Inversion Effects

    ERIC Educational Resources Information Center

    Rieth, Cory A.; Huber, David E.

    2010-01-01

    Immediate repetition priming for faces was examined across a range of prime durations in a threshold identification task. Similar to word repetition priming results, short duration face primes produced positive priming whereas long duration face primes eliminated or reversed this effect. A habituation model of such priming effects predicted that…

  3. Oligomerizations of deoxyadenosine bis-phosphates and of their 3-prime-5-prime, 3-prime-3-prime, and 5-prime-5-prime dimers - Effects of a pyrophosphate-linked, poly(T) analog

    NASA Technical Reports Server (NTRS)

    Visscher, J.; Bakker, C. G.; Schwartz, Alan W.

    1990-01-01

    The effect of a 3-prime-5-prime pyrophosphate-linked oligomer of pTp on oligomerizations of pdAp and of its 3-prime-5-prime, 3-prime-3-prime, and 5-prime-5-prime dimers was investigated, using HPLC to separate the reaction mixtures; peak detection was by absorbance monitoring at 254 nm. It was expected that the dimers would form stable complexes with the template, with the degree of stability depending upon the internal linkage of each dimer. It was found that, although the isomers differ substantially in their oligomerization behavior in the absence of template, the analog-template catalyzes the oligomerization to about the same extent in all three cases.

  4. Structural Priming: A Critical Review

    PubMed Central

    Pickering, Martin J.; Ferreira, Victor S.

    2009-01-01

    Repetition is a central phenomenon of behavior, and researchers make extensive use of it to illuminate psychological functioning. In the language sciences, a ubiquitous form of such repetition is structural priming, a tendency to repeat or better process a current sentence because of its structural similarity to a previously experienced (“prime”) sentence (Bock, 1986). The recent explosion of research in structural priming has made it the dominant means of investigating the processes involved in the production (and increasingly, comprehension) of complex expressions such as sentences. This review considers its implications for the representation of syntax and the mechanisms of production, comprehension, and their relationship. It then addresses the potential functions of structural priming, before turning to its implications for first language acquisition, bilingualism, and aphasia We close with theoretical and empirical recommendations for future investigations. PMID:18444704

  5. Priming in Systemic Plant Immunity

    SciTech Connect

    Jung, Ho Won; Tschaplinski, Timothy J; Wang, Lin; Glazebrook, Jane; Greenberg, Jean T.

    2009-01-01

    Upon local infection, plants possess inducible systemic defense responses against their natural enemies. Bacterial infection results in the accumulation to high levels of the mobile metabolite C9-dicarboxylic acid azelaic acid in the vascular sap of Arabidopsis. Azelaic acid confers local and systemic resistance against Pseudomonas syringae. The compound primes plants to strongly accumulate salicylic acid (SA), a known defense signal, upon infection. Mutation of a gene induced by azelaic acid (AZI1) results in the specific loss in plants of systemic immunity triggered by pathogen or azelaic acid and of the priming of SA induction. AZI1, a predicted secreted protein, is also important for generating vascular sap that confers disease resistance. Thus, azelaic acid and AZI1 comprise novel components of plant systemic immunity involved in priming defenses.

  6. Structural defects in bulk GaN

    NASA Astrophysics Data System (ADS)

    Liliental-Weber, Z.; dos Reis, R.; Mancuso, M.; Song, C. Y.; Grzegory, I.; Porowski, S.; Bockowski, M.

    2014-10-01

    Transmission Electron Microscopy (TEM) studies of undoped and Mg doped GaN layers grown on the HVPE substrates by High Nitrogen Pressure Solution (HNPS) with the multi-feed-seed (MFS) configuration are shown. The propagation of dislocations from the HVPE substrate to the layer is observed. Due to the interaction between these dislocations in the thick layers much lower density of these defects is observed in the upper part of the HNPS layers. Amorphous Ga precipitates with attached voids pointing toward the growth direction are observed in the undoped layer. This is similar to the presence of Ga precipitates in high-pressure platelets, however the shape of these precipitates is different. The Mg doped layers do not show Ga precipitates, but MgO rectangular precipitates are formed, decorating the dislocations. Results of TEM studies of HVPE layers grown on Ammonothermal substrates are also presented. These layers have superior crystal quality in comparison to the HNPS layers, as far as density of dislocation is concern. Occasionally some small inclusions can be found, but their chemical composition was not yet determined. It is expected that growth of the HNPS layers on these substrate will lead to large layer thickness obtained in a short time and with high crystal perfection needed in devices.

  7. Characterization of electrospun GaN nanofibers

    NASA Astrophysics Data System (ADS)

    Ramos, Idalia; Melendez, Anamaris; Morales, Kristle; Campo, Eva M.; Santiago-Aviles, Jorge J.

    2010-03-01

    Gallium Nitride shows characteristics pertinent to optoelectronics and gas sensing applications. Nanofibers have been produced using electrospinning and a precursor composed of Gallium (III) Nitrate Hydrate dissolved in Dimethyl-Acetamide and Cellulose Acetate in Acetone and DMA. The resulting nanofibers were sintered at 400C in nitrogen for one hour to decompose the polymer, the furnace atmosphere switched to ammonia and the fibers sintered for periods of 3, 5 and 7 hrs at 900C. They showed morphologies with unclear dependence on processing parameters. X-ray Diffraction revealed the evolution towards wurtzite phase through annealing. From line broadening we estimate a crystalline domain size of about 12 nm. Transmission Electron Microscopy suggests nucleation and growth of X-tallites while Fourier-Transform Infrared Spectroscopy and Ultraviolet-Visible Spectroscopy confirm the material evolution towards crystallinity and the production of wurtzite GaN nanofibers. I-V characteristics of single nanofibers show linearity with increments in conductivity for those fibers ammoniated during longer periods of time. Ongoing efforts aim at improving fabrication, sensing and photoluminescence characterization.

  8. Desorption Induced Formation of Negative Nanowires in GaN

    SciTech Connect

    Stach, E.A.; Kim, B.-J.

    2011-06-01

    We report in-situ transmission electron microscopy studies of the formation of negative nanowires created by thermal decomposition of single crystal GaN. During annealing, vertical negative nanowires are formed in [0 0 0 1] by preferential dissociation of GaN along the 1 0 {bar 1} 0 prism planes, while lateral negative nanowires grow in close-packed 1 0 {bar 1} 0 by the self-catalytic solid-liquid-vapor (SLV) mechanism. Our quantitative measurements show that the growth rates of the laterally grown negative nanowires are independent of the wire diameter, indicating that the rate-limiting step is the decomposition of GaN on the surface of the Ga droplets that catalyze their creation. These nanoscale features offer controllable templates for the creation and integration of a broad range of nanoscale materials systems, with potential applications in nanoscale fluidics.

  9. Application of GaN for photoelectrolysis of water

    NASA Astrophysics Data System (ADS)

    Puzyk, M. V.; Usikov, A. S.; Kurin, S. Yu; Puzyk, A. M.; Fomichev, A. D.; Ermakov, I. A.; Kovalev, D. S.; Papchenko, B. P.; Helava, H.; Makarov, Yu N.

    2015-11-01

    GaN layers of n-type and p-type conductivity grown by HVPE on sapphire substrates were used as working electrodes for water electrolysis, photoelectrolysis and hydrogen gas generation. Specifically the water splitting process is discussed. Corrosion of the GaN materials is also considered. The hydrogen production rate under 365-nm UV LED irradiation of the GaN and external bias was 0.3 ml/(cm2*h) for an n-GaN photoanode (n∼8×1016 cm-3) in 1M Na2SO4 electrolyte and 1.2 ml/(cm2*h) for an n-GaN photoanode (n∼1×1017 cm-3) in 1M KOH electrolyte.

  10. Gate stack engineering for GaN lateral power transistors

    NASA Astrophysics Data System (ADS)

    Yang, Shu; Liu, Shenghou; Liu, Cheng; Hua, Mengyuan; Chen, Kevin J.

    2016-02-01

    Developing optimal gate-stack technology is a key to enhancing the reliability and performance of GaN insulated-gate devices for high-voltage power switching applications. In this paper, we discuss current challenges and review our recent progresses in gate-stack technology development toward high-performance and high-reliability GaN power devices, including (1) interface engineering that creates a high-quality dielectric/III-nitride interface with low trap density; (2) barrier-layer engineering that enables optimal trade-off between performance and stability; (3) bulk quality and reliability enhancement of the gate dielectric. These gate-stack techniques in terms of new process development and device structure design are valuable to realize highly reliable and competitive GaN power devices.

  11. Stability of Carbon Incorpoated Semipolar GaN(1101) Surface

    NASA Astrophysics Data System (ADS)

    Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori

    2011-08-01

    The structural stability of carbon incorporated GaN(1101) surfaces is theoretically investigated by performing first-principles pseudopotential calculations. The calculated surface formation energies taking account of the metal organic vapor phase epitaxy conditions demonstrate that several carbon incorporated surfaces are stabilized depending on the growth conditions. Using surface phase diagrams, which are obtained by comparing the calculated adsorption energy with vapor-phase chemical potentials, we find that the semipolar surface forms NH2 and CH2 below ˜1660 K while the polar GaN(0001) surface with CH3 is stabilized below ˜1550 K. This difference could be one of possible explanations for p-type doping on the semipolar GaN(1101) surface.

  12. Biosensors based on GaN nanoring optical cavities

    NASA Astrophysics Data System (ADS)

    Kouno, Tetsuya; Takeshima, Hoshi; Kishino, Katsumi; Sakai, Masaru; Hara, Kazuhiko

    2016-05-01

    Biosensors based on GaN nanoring optical cavities were demonstrated using room-temperature photoluminescence measurements. The outer diameter, height, and thickness of the GaN nanorings were approximately 750-800, 900, and 130-180 nm, respectively. The nanorings functioned as whispering-gallery-mode (WGM)-type optical cavities and exhibited sharp resonant peaks like lasing actions. The evanescent component of the WGM was strongly affected by the refractive index of the ambient environment, the type of liquid, and the sucrose concentration of the analyzed solution, resulting in shifts of the resonant wavelengths. The results indicate that the GaN nanorings can potentially be used in sugar sensors of the biosensors.

  13. Desorption induced formation of negative nanowires in GaN

    NASA Astrophysics Data System (ADS)

    Kim, Bong-Joong; Stach, Eric A.

    2011-06-01

    We report in-situ transmission electron microscopy studies of the formation of negative nanowires created by thermal decomposition of single crystal GaN. During annealing, vertical negative nanowires are formed in [0 0 0 1] by preferential dissociation of GaN along the {1 0 1¯ 0} prism planes, while lateral negative nanowires grow in close-packed <1 0 1¯ 0> by the self-catalytic solid-liquid-vapor (SLV) mechanism. Our quantitative measurements show that the growth rates of the laterally grown negative nanowires are independent of the wire diameter, indicating that the rate-limiting step is the decomposition of GaN on the surface of the Ga droplets that catalyze their creation. These nanoscale features offer controllable templates for the creation and integration of a broad range of nanoscale materials systems, with potential applications in nanoscale fluidics.

  14. GaN nanowire tips for nanoscale atomic force microscopy.

    PubMed

    Behzadirad, Mahmoud; Nami, Mohsen; Rishinaramagalam, Ashwin; Feezell, Daniel; Busani, Tito

    2017-04-07

    Imaging of high-aspect-ratio nanostructures with sharp edges and straight walls in nanoscale metrology by Atomic Force Microscopy (AFM) has been challenging due to the mechanical properties and conical geometry of the majority of available commercial tips. Here we report on the fabrication of GaN probes for nanoscale metrology of high-aspect-ratio structures to enhance the resolution of AFM imaging and improve the durability of AFM tips. GaN nanowires (NWs) were fabricated using bottom-up and top-down techniques and bonded to Si cantilevers to scan vertical trenches on Si substrates. Over several scans, the GaN probes demonstrated excellent durability while scanning uneven structures and showed resolution enhancements in topography images, independent of scan direction, compared to commercial Si tips.

  15. Mg doping and its effect on the semipolar GaN(1122) growth kinetics

    SciTech Connect

    Lahourcade, L.; Wirthmueller, A.; Monroy, E.; Chauvat, M. P.; Ruterana, P.; Laufer, A.; Eickhoff, M.

    2009-10-26

    We report the effect of Mg doping on the growth kinetics of semipolar GaN(1122) synthesized by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN(1122). We observe an enhancement of Mg incorporation in GaN(1122) compared to GaN(0001). Typical structural defects or polarity inversion domains found in Mg-doped GaN(0001) were not observed for the semipolar films investigated in the present study.

  16. Conductivity based on selective etch for GaN devices and applications thereof

    DOEpatents

    Zhang, Yu; Sun, Qian; Han, Jung

    2015-12-08

    This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm.sup.2) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

  17. A DFT study on NEA GaN photocathode with an ultrathin n-type Si-doped GaN cap layer

    NASA Astrophysics Data System (ADS)

    Xia, Sihao; Liu, Lei; Kong, Yike; Diao, Yu

    2016-10-01

    Due to the drawbacks of conventional negative electron affinity (NEA) GaN photocathodes activated by Cs or Cs/O, a new-type NEA GaN photocathodes with heterojunction surface dispense with Cs activation are proposed. This structure can be obtained through the coverage of an ultrathin n-type Si-doped GaN cap layer on the p-type Mg-doped GaN emission layer. The influences of the cap layer on the photocathode are calculated using DFT. This study indicates that the n-type cap layer can promote the photoemission characteristics of GaN photocathode and demonstrates the probability of the preparation of a NEA GaN photocathode with an n-type cap layer.

  18. On the control of single-prime negative priming: the effects of practice and time course.

    PubMed

    Chao, Hsuan-Fu

    2009-09-01

    Single-prime negative priming refers to the phenomenon wherein repetition of a prime as the probe target results in delayed response. Sometimes this effect has been found to be contingent on participants' unawareness of the primes, and sometimes it has not. Further, sometimes this effect has been found to be eliminated when the prime could predict the following probe target, and sometimes it has not. An integrative account is postulated to account for these findings. Three experiments supported this account by demonstrating that (a) regardless of the proportion of prime repetition, negative priming was the default effect; (b) the control mechanism was triggered to activate the prime after there was enough practice for the detection of the contingency between the prime and probe; and (c) it took time for the control mechanism to overcome the negative-priming effect and produce a positive-priming effect.

  19. PREFACE: SANS-YuMO User Meeting at the Start-up of Scientific Experiments on the IBR-2M Reactor: Devoted to the 75th anniversary of Yu M Ostanevich's birth

    NASA Astrophysics Data System (ADS)

    Gordely, Valentin; Kuklin, Alexander; Balasoiu, Maria

    2012-03-01

    The Second International Workshop 'SANS-YuMO User Meeting at the Start-up of Scientific Experiments on the IBR-2M Reactor', devoted to the 75th anniversary of the birth of Professor Yu M Ostanevich (1936-1992), an outstanding neutron physicist and the founder of small-angle neutron scattering (field, group, and instrument) at JINR FLNPh, was held on 27-30 May at the Frank Laboratory of Neutron Physics. The first Workshop was held in October 2006. Research groups from different neutron centers, universities and research institutes across Europe presented more than 35 oral and poster presentations describing scientific and methodological results. Most of them were obtained with the help of the YuMO instrument before the IBR-2 shutdown in 2006. For the last four years the IBR-2 reactor has been shut down for refurbishment. At the end of 2010 the physical launch of the IBR-2M reactor was finally realized. Nowadays the small-angle neutron scattering (SANS) technique is applied to a wide range of scientific problems in condensed matter, soft condensed matter, biology and nanotechnology, and despite the fact that there are currently over 30 SANS instruments in operation worldwide at both reactor and spallation sources, the demand for beam-time is considerably higher than the time available. It must be remembered, however, that as the first SANS machine on a steady-state reactor was constructed at the Institute Laue Langevin, Grenoble, the first SANS instrument on a 'white' neutron pulsed beam was accomplished at the Joint Institute for Nuclear Research at the IBR-30 reactor, beamline N5. During the meeting Yu M Ostanevich's determinative and crucial contribution to the construction of spectrometers at the IBR-2 high-pulsed reactor was presented, as well as his contribution to the development of the time-of-flight (TOF) small-angle scattering technique, and a selection of other scientific areas. His leadership and outstanding scientific achievements in applications of the

  20. Critical issues for homoepitaxial GaN growth by molecular beam epitaxy on hydride vapor-phase epitaxy-grown GaN substrates

    NASA Astrophysics Data System (ADS)

    Storm, D. F.; Hardy, M. T.; Katzer, D. S.; Nepal, N.; Downey, B. P.; Meyer, D. J.; McConkie, Thomas O.; Zhou, Lin; Smith, David J.

    2016-12-01

    While the heteroepitaxial growth of gallium nitride-based materials and devices on substrates such as SiC, sapphire, and Si has been well-documented, the lack of a cost-effective source of bulk GaN crystals has hindered similar progress on homoepitaxy. Nevertheless, freestanding GaN wafers are becoming more widely available, and there is great interest in growing GaN films and devices on bulk GaN substrates, in order to take advantage of the greatly reduced density of threading dislocations, particularly for vertical devices. However, homoepitaxial GaN growth is far from a trivial task due to the reactivity and different chemical sensitivities of N-polar (000_1) and Ga-polar (0001) GaN surfaces, which can affect the microstructure and concentrations of impurities in homoepitaxial GaN layers. In order to achieve high quality, high purity homoepitaxial GaN, it is necessary to investigate the effect of the ex situ wet chemical clean, the use of in situ cleaning procedures, the sensitivity of the GaN surface to thermal decomposition, and the effect of growth temperature. We review the current understanding of these issues with a focus on homoepitaxial growth of GaN by molecular beam epitaxy (MBE) on c-plane surfaces of freestanding GaN substrates grown by hydride vapor phase epitaxy (HVPE), as HVPE-grown substrates are most widely available. We demonstrate methods for obtaining homoepitaxial GaN layers by plasma-assisted MBE in which no additional threading dislocations are generated from the regrowth interface and impurity concentrations are greatly reduced.

  1. Development of Partial-Charge Potential for GaN

    SciTech Connect

    Gao, Fei; Devanathan, Ram; Oda, Takuji; Weber, William J.

    2006-09-01

    Partial-charged potentials for GaN are systematically developed that describes a wide range of structural properties, where the reference data for fitting the potential parameters are taken from ab initial calculations or experiments. The present potential model provides a good fit to different structural geometries and high pressure phases of GaN. The high-pressure transition from wurtzite to rock-salt structure is correctly described yielding the phase transition pressure of about 55 GPa, and the calculated volume change at the transition is in good agreement with experimental data. The results are compared with those obtained by ab initio simulations.

  2. Transmission electron microscopy of electrospun GaN nanofibers

    NASA Astrophysics Data System (ADS)

    Robles-García, Joshua L.; Meléndez, Anamaris; Yates, Douglas; Santiago-Avilés, Jorge J.; Ramos, Idalia; Campo, Eva M.

    2011-06-01

    We have reported earlier progress in producing polycrystalline wurtzite-polymorph and photo-conductive GaN nanofibers by electrospinning. This paper shows grain stacking during heat treatment and suggests the need to understand nucleation and grain growth following electrospinning. Transmission Electron Microscopy (TEM) analysis of GaN shows brittle fibers, grain stacking, and unfinished grain nucleation. X-Ray Diffraction analysis confirmed dominant hexagonal 101-wurtzite preferential overall orientation and the incipient grains are of high crystalline quality as seen by high resolution TEM.

  3. Dislocation luminescence in GaN single crystals under nanoindentation

    PubMed Central

    2014-01-01

    This work presents an experimental study on the dislocation luminescence in GaN by nanoindentation, cathodoluminescence, and Raman. The dislocation luminescence peaking at 3.12 eV exhibits a series of special properties in the cathodoluminescence measurements, and it completely disappears after annealing at 500°C. Raman spectroscopy shows evidence for existence of vacancies in the indented region. A comprehensive investigation encompassing cathodoluminescence, Raman, and annealing experiments allow the assignment of dislocation luminescence to conduction-band-acceptor transition involving Ga vacancies. The nanoscale plasticity of GaN can be better understood by considering the dislocation luminescence mechanism. PMID:25593548

  4. Redistribution of Implanted Dopants in GaN

    SciTech Connect

    Fu, M.; Gao, X.A.; Han, J.; Pearton, S.J.; Rieger, D.J.; Scarvepalli, V. Sekhar, J.A.; Shul, R.J.; Singh, R.K.; Wilson, R.G.; Zavada, J.M.; Zolper, J.C.

    1998-11-20

    Donor (S, Se and Te) and acceptor (Mg, Be and C) dopants have been implanted into GaN at doses of 3-5x1014 cm-2 and annealed at temperatures up to 1450 *C. No redistribution of any of the elements is detectable by Secondary Ion Mass Spectrometry, except for Be, which displays an apparent damage-assisted diffusion at 900 "C. At higher temperatures there is no further movement of the Be, suggesting that the point defect flux that assists motion at lower temperatures has been annealed. Effective diffusivities are <2X 1013 cm2.sec-1 at 1450 `C for each of the dopants in GaN.

  5. Ferromagnetism in undoped One-dimensional GaN Nanowires

    SciTech Connect

    Jeganathan, K. E-mail: jagan@physics.bdu.ac.in; Purushothaman, V.; Debnath, R.; Arumugam, S.

    2014-05-15

    We report an intrinsic ferromagnetism in vertical aligned GaN nanowires (NW) fabricated by molecular beam epitaxy without any external catalyst. The magnetization saturates at ∼0.75 × emu/gm with the applied field of 3000 Oe for the NWs grown under the low-Gallium flux of 2.4 × 10{sup −8} mbar. Despite a drop in saturation magnetization, narrow hysteresis loop remains intact regardless of Gallium flux. Magnetization in vertical standing GaN NWs is consistent with the spectral analysis of low-temperature photoluminescence pertaining to Ga-vacancies associated structural defects at the nanoscale.

  6. GaN surface states investigated by electrochemical studies

    NASA Astrophysics Data System (ADS)

    Winnerl, Andrea; Garrido, Jose A.; Stutzmann, Martin

    2017-03-01

    We present a systematic study of electrochemically active surface states on MOCVD-grown n-type GaN in aqueous electrolytes using cyclic voltammetry and impedance spectroscopy over a wide range of potentials and frequencies. In order to alter the surface states, the GaN samples are either etched or oxidized, and the influence of the surface treatment on the defect-mediated charge transfer to the electrolyte is investigated. Etching in HCl removes substoichiometric GaO x , and leads to a pronounced density of electrochemically active surface states. Oxidation effectively removes these surface states.

  7. Chemical mechanical polishing of freestanding GaN substrates

    NASA Astrophysics Data System (ADS)

    Huaiyue, Yan; Xiangqian, Xiu; Zhanhui, Liu; Rong, Zhang; Xuemei, Hua; Zili, Xie; Ping, Han; Yi, Shi; Youdou, Zheng

    2009-02-01

    Chemical mechanical polishing (CMP) has been used to produce smooth and scratch-free surfaces for GaN. In the aqueous solution of KOH, GaN is subjected to etching. At the same time, all surface irregularities, including etch pyramids, roughness after mechanical polishing and so on will be removed by a polishing pad. The experiments had been performed under the condition of different abrasive particle sizes of the polishing pad. Also the polishing results for different polishing times are analyzed, and chemical mechanical polishing resulted in an average root mean square (RMS) surface roughness of 0.565 nm, as measured by atomic force microscopy.

  8. Self-assembled GaN hexagonal micropyramid and microdisk

    SciTech Connect

    Lo Ikai; Hsieh, C.-H.; Hsu, Y.-C.; Pang, W.-Y.; Chou, M.-C.

    2009-02-09

    The self-assembled GaN hexagonal micropyramid and microdisk were grown on LiAlO{sub 2} by plasma-assisted molecular-beam epitaxy. It was found that the (0001) disk was established with the capture of N atoms by most-outside Ga atoms as the (1x1) surface was constructing, while the pyramid was obtained due to the missing of most-outside N atoms. The intensity of cathode luminescence excited from the microdisk was one order of amplitude greater than that from M-plane GaN.

  9. Highly transparent ammonothermal bulk GaN substrates

    SciTech Connect

    Jiang, WK; Ehrentraut, D; Downey, BC; Kamber, DS; Pakalapati, RT; Do Yoo, H; D'Evelyn, MP

    2014-10-01

    A novel apparatus has been employed to grow ammonothermal (0001) gallium nitride (GaN) with diameters up to 2 in The crystals have been characterized by x-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), and optical spectroscopy. High crystallinity GaN with FWHM values about 20-50 arcsec and dislocation densities below 1 x 10(5) cm(-2) have been obtained. High optical transmission was achieved with an optical absorption coefficient below 1 cm(-1) at a wavelength of 450 nm. (C) 2014 Elsevier B.V. All rights reserved.

  10. GaN nanowire arrays by a patterned metal-assisted chemical etching

    NASA Astrophysics Data System (ADS)

    Wang, K. C.; Yuan, G. D.; Wu, R. W.; Lu, H. X.; Liu, Z. Q.; Wei, T. B.; Wang, J. X.; Li, J. M.; Zhang, W. J.

    2016-04-01

    We developed an one-step and two-step metal-assisted chemical etching method to produce self-organized GaN nanowire arrays. In one-step approach, GaN nanowire arrays are synthesized uniformly on GaN thin film surface. However, in a two-step etching processes, GaN nanowires are formed only in metal uncovered regions, and GaN regions with metal-covering show nano-porous sidewalls. We propose that nanowires and porous nanostructures are tuned by sufficient and limited etch rate, respectively. PL spectra shows a red-shift of band edge emission in GaN nanostructures. The formation mechanism of nanowires was illustrated by two separated electrochemical reactions occur simultaneously. The function of metals and UV light was illustrated by the scheme of potential relationship between energy bands in Si, GaN and standard hydrogen electrode potential of solution and metals.

  11. Prime Suspect, Second Row Center

    ERIC Educational Resources Information Center

    Laird, Ellen A.

    2011-01-01

    His father had been hacked to death in his own bed with an ax the previous November. His mother was similarly brutalized and left for dead with her husband but survived. On the last Monday of that August, after several months and many investigative twists, turns, and fumbles, there sat the son--the prime suspect--in Ellen Laird's literature class,…

  12. The Search for Prime Numbers.

    ERIC Educational Resources Information Center

    Pomerance, Carl

    1982-01-01

    Until recently the testing of a 100-digit number to determine whether it is prime or composite could have taken a century. However, in the past two years a method has been developed enabling a computer to determine the primality of an arbitrary number in about 40 seconds of running time. (Author/JN)

  13. Evaluative Priming in the Pronunciation Task.

    PubMed

    Klauer, Karl Christoph; Becker, Manuel; Spruyt, Adriaan

    2016-01-01

    We replicated and extended a study by Spruyt and Hermans (2008) in which picture primes engendered an evaluative-priming effect on the pronunciation of target words. As preliminary steps, we assessed data reproducibility of the original study, conducted Pilot Study I to identify highly semantically related prime-target pairs, reanalyzed the original data excluding such pairs, conducted Pilot Study II to demonstrate that we can replicate traditional associative priming effects in the pronunciation task, and conducted Pilot Study III to generate relatively unrelated sets of prime pictures and target words. The main study comprised three between-participants conditions: (1) a close replication of the original study, (2) the same condition excluding highly related prime-target pairs, and (3) a condition based on the relatively unrelated sets of prime pictures and target words developed in Pilot Study III. There was little evidence for an evaluative priming effect independent of semantic relatedness.

  14. Teachers' Use of a Pedagogical Framework for Improvement in Mathematics Teaching: Case Studies from YuMi Deadly Maths

    ERIC Educational Resources Information Center

    Carter, Merilyn; Cooper, Tom; Anderson, Robyn

    2016-01-01

    This paper describes the pedagogical framework used by YuMi Deadly Maths, a school change process used to improve mathematics teaching and thus enhance employment and life chances for socially disadvantaged students. The framework, called the RAMR cycle, is capable of being used by mathematics teachers for planning and delivering lessons and units…

  15. Main features of the new software control system for the YuMO instrument

    NASA Astrophysics Data System (ADS)

    Kirilov, A. S.

    2012-03-01

    During the last years the new software instrumental complex Sonix+ has been developed at FLNP JINR to replace the former Sonix control system [1]. This complex has been tested at a number of IBR-2 instruments (REMUR, NERA-PR) and on instruments at other centers - KIA, Moscow (MOND), etc. We plan to install the new complex at the YuMO instrument as well. The Sonix+ is implemented on the PC/Windows XP platform, whereas the Sonix is based on the VME/Os-9 obsolete platform. The Sonix+ [1] has been designed considering the experience of long-term operation of the predecessor and recent trends. The paper is devoted to the main features of the new software and the comparison with the former one.

  16. Yu-Shiba-Rusinov states and topological superconductivity in Ising paired superconductors

    NASA Astrophysics Data System (ADS)

    Sharma, Girish; Tewari, Sumanta

    2016-09-01

    An unusual form of superconductivity, called Ising superconductivity, has recently been uncovered in mono- and few-layered transition metal dichalcogenides. This 2D superconducting state is characterized by the so-called Ising spin-orbit coupling (SOC), which produces strong oppositely oriented effective Zeeman fields perpendicular to the 2D layer in opposite momentum space valleys. We examine the Yu-Shiba-Rusinov (YSR) bound states localized at magnetic impurities in Ising superconductors and show that the unusual SOC manifests itself in unusually strong anisotropy in magnetic field response observable in STM experiments. For a chain of magnetic impurities with moments parallel to the plane of Ising superconductors we show that the low energy YSR band hosts topological superconductivity and Majorana excitations as a direct manifestation of topological effects induced by Ising spin-orbit coupling.

  17. Scale interactions in sustaining persistent torrential rainfall events during the Mei-yu season

    NASA Astrophysics Data System (ADS)

    Fu, Shen-Ming; Sun, Jian-Hua; Ling, Jian; Wang, Hui-Jie; Zhang, Yuan-Chun

    2016-11-01

    Energy budgets based on the temporal scale separation were used to investigate two persistent torrential rainfall events over the Yangtze River Basin during the 2010 Mei-yu season. Interactions between the precipitation-related eddy flows and their background circulations were analyzed quantitatively to show the corresponding physical scenario. During the persistent precipitation, the precipitation-related eddy flows and their background circulations sustained their respective energy through different mechanisms. For background circulations, the baroclinic energy conversion and the energy transport dominated their maintenance. In contrast, for precipitation-related eddy flows, the upper, middle, and lower troposphere showed significantly different energy paths: in the upper troposphere, a remarkable downscaled energy cascade process (ECP) of available potential energy occurred, which favored the maintenance of upper level wind perturbations through the baroclinic energy conversion; in the middle troposphere, the energy transport controlled the evolution of eddy flows; in the lower troposphere, a significant downscaled ECP of kinetic energy maintained its intensity, which directly favored the sustainment of the Mei-yu front and the lower level jet. These downscaled ECPs, which reflected the direct effects of background circulations on the eddy flows, dominated the evolution of precipitation-related eddy flows. In contrast, although upscaled ECPs that indicated the feedback effects of eddy flows on their background circulations were also obvious, they were negligible in the variation of background circulations. The further analysis indicates that whether the background circulations could transfer their energy to the precipitation-related eddy flows was determined by their configurations relative to the eddy flows.

  18. Competition Effects in Phonological Priming: The Role of Mismatch Position between Primes and Targets

    ERIC Educational Resources Information Center

    Dufour, Sophie; Peereman, Ronald

    2009-01-01

    In three experiments, we examined lexical competition effects using the phonological priming paradigm in a shadowing task. Experiments 1A and 1B showed that an inhibitory priming effect occurred when the primes mismatched the targets on the last phoneme (/bagar/-/bagaj/). In contrast, a facilitatory priming effect was observed when the primes…

  19. Evidence for Episodic Retrieval of Inadequate Prime Responses in Auditory Negative Priming

    ERIC Educational Resources Information Center

    Mayr, Susanne; Buchner, Axel

    2006-01-01

    Four experiments are reported in which the mechanisms underlying auditory negative priming were investigated. In Experiments 1A and 1B, preprime-prime intervals and prime-probe intervals were manipulated.The ratio between the 2 intervals determined the size of the negative priming effect. Results are compatible with the episodic retrieval account,…

  20. Affective Priming with Associatively Acquired Valence

    ERIC Educational Resources Information Center

    Aguado, Luis; Pierna, Manuel; Saugar, Cristina

    2005-01-01

    Three experiments explored the effect of affectively congruent or incongruent primes on evaluation responses to positive or negative valenced targets (the "affective priming" effect). Experiment 1 replicated the basic affective priming effect with Spanish nouns: reaction time for evaluative responses (pleasant/unpleasant) were slower on…

  1. Priming Lexical Stress in Reading Italian Aloud

    ERIC Educational Resources Information Center

    Sulpizio, Simone; Job, Remo; Burani, Cristina

    2012-01-01

    Two experiments using a lexical priming paradigm investigated how stress information is processed in reading Italian words. In both experiments, prime and target words either shared the stress pattern or they had different stress patterns. We expected that lexical activation of the prime would favour the assignment of congruent stress to the…

  2. Structural Priming and Second Language Learning

    ERIC Educational Resources Information Center

    Shin, Jeong-Ah; Christianson, Kiel

    2012-01-01

    Structural priming (or syntactic priming) is a speaker's tendency to reuse the same structural pattern as one that was previously encountered (Bock, 1986). This study investigated (a) whether the implicit learning processes involved in long-lag structural priming lead to differential second language (L2) improvement in producing two structural…

  3. Spatial priming in ecologically relevant reference frames.

    PubMed

    Tower-Richardi, Sarah M; Leber, Andrew B; Golomb, Julie D

    2016-01-01

    In recent years, researchers have observed many phenomena demonstrating how the visual system exploits spatial regularities in the environment in order to benefit behavior. In this paper, we question whether spatial priming can be considered one such phenomenon. Spatial priming is defined as a response time facilitation to a visual search target when its spatial position has been repeated in recent trials (Maljkovic & Nakayama, 1996, Perception & Psychophysics, 58, 977-991). Does this priming serve a behaviorally adaptive role or is it merely a byproduct of ongoing visual processing? Critically, an adaptive priming mechanism must actively transform visual inputs from native retinotopic (eye-centered) coordinates into ecologically relevant coordinates, e.g., spatiotopic (world-centered) and/or object-centered. In Experiment 1, we tested this hypothesis by having participants move their eyes between trials, which dissociated retinotopic and spatiotopic frames of reference. Results showed only weak retinotopic priming, but robust spatiotopic priming. The second experiment again had participants move their eyes between trials but also manipulated the placement of a grouped array of display objects from trial to trial. This allowed us to measure not just retinotopic and spatiotopic priming, but object-centered priming as well. Results from this experiment did not yield retinotopic priming but showed robust spatiotopic and object-centered priming. These findings demonstrate that spatial priming operates within ecologically relevant coordinate systems, and the findings support the notion that spatial priming serves an adaptive role in human behavior.

  4. Affective Priming with Auditory Speech Stimuli

    ERIC Educational Resources Information Center

    Degner, Juliane

    2011-01-01

    Four experiments explored the applicability of auditory stimulus presentation in affective priming tasks. In Experiment 1, it was found that standard affective priming effects occur when prime and target words are presented simultaneously via headphones similar to a dichotic listening procedure. In Experiment 2, stimulus onset asynchrony (SOA) was…

  5. Automatic non-associative semantic priming: episodic affective priming of naming responses.

    PubMed

    Spruyt, Adriaan; Hermans, Dirk; De Houwer, Jan; Eelen, Paul

    2004-05-01

    Affective priming for associatively unrelated prime-target pairs was investigated using (a) the naming task, (b) a short stimulus onset asynchrony (250 ms), and (c) primes that had acquired their affective connotation during a differential evaluative conditioning procedure. Despite the fact that the primes and the targets were related on the affective dimension only, significant priming emerged. This finding indicates that mere affective overlap is sufficient to produce automatic priming. As such, our results are in line with theoretical accounts of automatic priming that are based on semantic relatedness.

  6. Semantic priming in the prime task effect: evidence of automatic semantic processing of distractors.

    PubMed

    Marí-Beffa, P; Fuentes, L J; Catena, A; Houghton, G

    2000-06-01

    The automaticity of the semantic processing of words has been questioned because of the reduction of semantic priming when the prime word is processed nonsemantically--for example, in letter search (the prime task effect). In two experiments, prime distractor words produced semantic priming in a subsequent lexical decision task, but with the direction of priming (positive or negative) depending on the prime task. Lexico-semantic tasks produced negative semantic priming, whereas letter search produced positive semantic priming. These results are discussed in terms of task-based inhibition. We argue that, given the results from the distractors, the absence of semantic priming does not indicate an absence of semantic activation but reflects the action of control processes on prepotent responses when less practiced responses are needed.

  7. Basic ammonothermal GaN growth in molybdenum capsules

    NASA Astrophysics Data System (ADS)

    Pimputkar, S.; Speck, J. S.; Nakamura, S.

    2016-12-01

    Single crystal, bulk gallium nitride (GaN) crystals were grown using the basic ammonothermal method in a high purity growth environment created using a non-hermetically sealed molybdenum (Mo) capsule and compared to growths performed in a similarly designed silver (Ag) capsule and capsule-free René 41 autoclave. Secondary ion mass spectrometry (SIMS) analysis revealed transition metal free (<1×1017 cm-3) GaN crystals. Anomalously low oxygen concentrations ((2-6)×1018 cm-3) were measured in a {0001} seeded crystal boule grown using a Mo capsule, despite higher source material oxygen concentrations ((1-5)×1019 cm-3) suggesting that molybdenum (or molybdenum nitrides) may act to getter oxygen under certain conditions. Total system pressure profiles from growth runs in a Mo capsule system were comparable to those without a capsule, with pressures peaking within 2 days and slowly decaying due to hydrogen diffusional losses. Measured Mo capsule GaN growth rates were comparable to un-optimized growth rates in capsule-free systems and appreciably slower than in Ag-capsule systems. Crystal quality replicated that of the GaN seed crystals for all capsule conditions, with high quality growth occurring on the (0001) Ga-face. Optical absorption and impurity concentration characterization suggests reduced concentrations of hydrogenated gallium vacancies (VGa-Hx).

  8. Refractive index of erbium doped GaN thin films

    SciTech Connect

    Alajlouni, S.; Sun, Z. Y.; Li, J.; Lin, J. Y.; Jiang, H. X.; Zavada, J. M.

    2014-08-25

    GaN is an excellent host for erbium (Er) to provide optical emission in the technologically important as well as eye-safe 1540 nm wavelength window. Er doped GaN (GaN:Er) epilayers were synthesized on c-plane sapphire substrates using metal organic chemical vapor deposition. By employing a pulsed growth scheme, the crystalline quality of GaN:Er epilayers was significantly improved over those obtained by conventional growth method of continuous flow of reaction precursors. X-ray diffraction rocking curve linewidths of less than 300 arc sec were achieved for the GaN (0002) diffraction peak, which is comparable to the typical results of undoped high quality GaN epilayers and represents a major improvement over previously reported results for GaN:Er. Spectroscopic ellipsometry was used to determine the refractive index of the GaN:Er epilayers in the 1540 nm wavelength window and a linear dependence on Er concentration was found. The observed refractive index increase with Er incorporation and the improved crystalline quality of the GaN:Er epilayers indicate that low loss GaN:Er optical waveguiding structures are feasible.

  9. Photoluminescence of Zn-implanted GaN

    NASA Technical Reports Server (NTRS)

    Pankove, J. I.; Hutchby, J. A.

    1974-01-01

    The photoluminescence spectrum of Zn-implanted GaN peaks at 2.87 eV at room temperature. The emission efficiency decreases linearly with the logarithm of the Zn concentration in the range from 1 x 10 to the 18th to 20 x 10 to the 18th Zn/cu cm.

  10. Luminescence properties of defects in GaN

    NASA Astrophysics Data System (ADS)

    Reshchikov, Michael A.; Morkoç, Hadis

    2005-03-01

    Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The point defects include native isolated defects (vacancies, interstitial, and antisites), intentional or unintentional impurities, as well as complexes involving different combinations of the isolated defects. Further improvements in device performance and longevity hinge on an in-depth understanding of point defects and their reduction. In this review a comprehensive and critical analysis of point defects in GaN, particularly their manifestation in luminescence, is presented. In addition to a comprehensive analysis of native point defects, the signatures of intentionally and unintentionally introduced impurities are addressed. The review discusses in detail the characteristics and the origin of the major luminescence bands including the ultraviolet, blue, green, yellow, and red bands in undoped GaN. The effects of important group-II impurities, such as Zn and Mg on the photoluminescence of GaN, are treated in detail. Similarly, but to a lesser extent, the effects of

  11. Mechanism of stress control for GaN growth on Si using AlN interlayers

    NASA Astrophysics Data System (ADS)

    Suzuki, Michihiro; Nakamura, Akihiro; Nakano, Yoshiaki; Sugiyama, Masakazu

    2017-04-01

    For the purpose of controlling the wafer bow of GaN-on-Si structure, in situ curvature transient during the growth of a GaN layer on an AlN interlayer was investigated systematically by estimating the compressive strain applied to the GaN layer with the progress of the layer growth. The compressive strain was dependent on the morphology of the GaN surface prior to the growth of the AlN interlayer. It was found that the transition sequence from GaN growth to AlN growth induces roughening of the GaN surface and both high NH3 partial pressure and the short transition time were effective for reducing the roughness of the GaN surface beneath the AlN interlayer. The improved transition sequence increased the compressive strain in GaN by a factor of 2.5. The AlN grown at the same temperature as that of GaN was beneficial in both better surface morphology and the reduction of the transition time between GaN growth and AlN growth. With this high-temperature AlN interlayer, its thickness is another important factor governing the compressive strain in GaN. To get AlN relaxed for applying the compressive strain to GaN, the AlN layer should be thicker but too thick layer after relaxation results in surface roughening, which in turn introduces defects to the overlying GaN layer and reduces the compressive strain by partial lattice relaxation of GaN.

  12. Alignment control and atomically-scaled heteroepitaxial interface study of GaN nanowires.

    PubMed

    Liu, Qingyun; Liu, Baodan; Yang, Wenjin; Yang, Bing; Zhang, Xinglai; Labbé, Christophe; Portier, Xavier; An, Vladimir; Jiang, Xin

    2017-04-11

    Well-aligned GaN nanowires are promising candidates for building high-performance optoelectronic nanodevices. In this work, we demonstrate the epitaxial growth of well-aligned GaN nanowires on a [0001]-oriented sapphire substrate in a simple catalyst-assisted chemical vapor deposition process and their alignment control. It is found that the ammonia flux plays a key role in dominating the initial nucleation of GaN nanocrystals and their orientation. Typically, significant improvement of the GaN nanowire alignment can be realized at a low NH3 flow rate. X-ray diffraction and cross-sectional scanning electron microscopy studies further verified the preferential orientation of GaN nanowires along the [0001] direction. The growth mechanism of GaN nanowire arrays is also well studied based on cross-sectional high-resolution transmission electron microscopy (HRTEM) characterization and it is observed that GaN nanowires have good epitaxial growth on the sapphire substrate following the crystallographic relationship between (0001)GaN∥(0001)sapphire and (101[combining macron]0)GaN∥(112[combining macron]0)sapphire. Most importantly, periodic misfit dislocations are also experimentally observed in the interface region due to the large lattice mismatch between the GaN nanowire and the sapphire substrate, and the formation of such dislocations will favor the release of structural strain in GaN nanowires. HRTEM analysis also finds the existence of "type I" stacking faults and voids inside the GaN nanowires. Optical investigation suggests that the GaN nanowire arrays have strong emission in the UV range, suggesting their crystalline nature and chemical purity. The achievement of aligned GaN nanowires will further promote the wide applications of GaN nanostructures toward diverse high-performance optoelectronic nanodevices including nano-LEDs, photovoltaic cells, photodetectors etc.

  13. Substitutional and interstitial oxygen in wurtzite GaN

    NASA Astrophysics Data System (ADS)

    Wright, A. F.

    2005-11-01

    Density-functional theory was used to compute energy-minimum configurations and formation energies of substitutional and interstitial oxygen (O) in wurtzite GaN. The results indicate that O substituted at a N site (ON) acts as a single donor with the ionized state (ON+1) being the most stable O state in p-type GaN. In n-type GaN, interstitial O (OI) is predicted to be a double acceptor and O substituted at a Ga site (OGa) is predicted to be a triple acceptor. The formation energies of these two species are comparable to that of ON in n-type GaN and, as such, they should form and compensate the ON donors. The extent of compensation was estimated for both Ga-rich and N-rich conditions with a total O concentration of 1017cm-3. Ga-rich conditions yielded negligible compensation and an ON concentration in excess of 9.9×1016cm-3. N-rich conditions yielded a 25% lower ON concentration, due to the increased stability of OI and OGa relative to ON, and moderate compensation. These findings are consistent with experimental results indicating that O acts as a donor in GaN(O). Complexes of ON with the Mg acceptor and OI with the Si donor were examined. Binding energies for charge-conserving reactions were ⩾0.5eV, indicating that these complexes can exist in equilibrium at room temperature. Complexes of ON with the Ga vacancy in n-type GaN were also examined and their binding energies were 1.2 and 1.4eV, indicating that appreciable concentrations can exist in equilibrium even at elevated temperatures.

  14. Specific peptide for functionalization of GaN

    NASA Astrophysics Data System (ADS)

    Estephan, E.; Larroque, C.; Cloitre, T.; Cuisinier, F. J. G.; Gergely, C.

    2008-04-01

    Nanobiotechnology aims to exploit biomolecular recognition and self-assembly capabilities for integrating advanced materials into medicine and biology. However frequent problems are encountered at the interface of substrate-biological molecule, as the direct physical adsorption of biological molecules is dependent of unpredictable non-specific interactions with the surface, often causing their denaturation. Therefore, a proper functionalization of the substrate should avoid a loss of biological activity. In this work we address the functionalization of the semiconductor GaN (0001) for biosensing applications. The basic interest of using III-V class semiconductors is their good light emitting properties and a fair chemical stability that allows various applications of these materials. The technology chosen to elaborate GaN-specific peptides is the combinatorial phage-display method, a biological screening procedure based on affinity selection. An M13 bacteriophage library has been used to screen 10 10 different peptides against the GaN (0001) surface to finally isolate one specific peptide. The preferential attachment of the biotinylated selected peptide onto the GaN (0001), in close proximity to a surface of different chemical and structural composition has been demonstrated by fluorescence microscopy. Further physicochemical studies have been initiated to evaluate the semiconductor-peptide interface and understand the details in the specific recognition of peptides for semiconductor substrates. Fourier Transform Infrared spectroscopy in Attenuated Total Reflection mode (FTIR-ATR) has been employed to prove the presence of peptides on the surface. Our Atomic Force Microscopy (AFM) studies on the morphology of the GaN surface after functionalization revealed a total surface coverage by a very thin, homogeneous peptide layer. Due to its good biocompatibility, functionalized GaN devices might evolve in a new class of implantable biosensors for medical applications.

  15. Polyurethane Self-Priming Topcoats

    DTIC Science & Technology

    1992-06-23

    Approved for public release; distribution is unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT A corrosion -resistant coating which can be applied directly...57] ABSTRACT A corrosion -resistant coating which can be applied directly to a surface as a self-priming topcoat compris- ing from about 10 to 90... corrosion -inhibiting pigments consisting The invention described herein mav be manufactured 5 «»eniially of ar alkaline earth metal or zinc phosphate

  16. Maglev ready for prime time.

    SciTech Connect

    Rote, D. M.; Johnson, L. R.; Energy Systems

    2003-01-01

    Putting Maglev on Track' (Issues, Spring 1990) observed that growing airline traffic and associated delays were already significant and predicted that they would worsen. The article argued that a 300-mile-per-hour (mph) magnetic levitation (maglev) system integrated into airport and airline operations could be a part of the solution. Maglev was not ready for prime time in 1990, but it is now.

  17. KAPAO Prime: Design and Simulation

    NASA Astrophysics Data System (ADS)

    McGonigle, Lorcan; Choi, P. I.; Severson, S. A.; Spjut, E.

    2013-01-01

    KAPAO (KAPAO A Pomona Adaptive Optics instrument) is a dual-band natural guide star adaptive optics system designed to measure and remove atmospheric aberration over UV-NIR wavelengths from Pomona College’s telescope atop Table Mountain. We present here, the final optical system, KAPAO Prime, designed in Zemax Optical Design Software that uses custom off-axis paraboloid mirrors (OAPs) to manipulate light appropriately for a Shack-Hartman wavefront sensor, deformable mirror, and science cameras. KAPAO Prime is characterized by diffraction limited imaging over the full 81” field of view of our optical camera at f/33 as well as over the smaller field of view of our NIR camera at f/50. In Zemax, tolerances of 1% on OAP focal length and off-axis distance were shown to contribute an additional 4 nm of wavefront error (98% confidence) over the field of view of our optical camera; the contribution from surface irregularity was determined analytically to be 40nm for OAPs specified to λ/10 surface irregularity (632.8nm). Modeling of the temperature deformation of the breadboard in SolidWorks revealed 70 micron contractions along the edges of the board for a decrease of 75°F when applied to OAP positions such displacements from the optimal layout are predicted to contribute an additional 20 nanometers of wavefront error. Flexure modeling of the breadboard due to gravity is on-going. We hope to begin alignment and testing of KAPAO Prime in Q1 2013.

  18. KAPAO Prime: Design and Simulation

    NASA Astrophysics Data System (ADS)

    McGonigle, Lorcan

    2012-11-01

    KAPAO (KAPAO A Pomona Adaptive Optics instrument) is a dual-band natural guide star adaptive optics system designed to measure and remove atmospheric aberration from Pomona College's telescope atop Table Mountain. We present here, the final optical system, referred to as Prime, designed in Zemax Optical Design Software. Prime is characterized by diffraction limited imaging over the full 73'' field of view of our Andor Camera at f/33 as well as for our NIR Xenics camera at f/50. In Zemax, tolerances of 1% on OAP focal length and off-axis distance were shown to contribute an additional 4 nm of wavefront error (98% confidence) over the field of view of the Andor camera; the contribution from surface irregularity was determined analytically to be 40nm for OAPs specified to l/10 surface irregularity. Modeling of the temperature deformation of the breadboard in SolidWorks revealed 70 micron contractions along the edges of the board for a decrease of 75 F; when applied to OAP positions such displacements from the optimal layout are predicted to contribute an additional 20 nanometers of wavefront error. Flexure modeling of the breadboard due to gravity is on-going. We hope to begin alignment and testing of ``Prime'' in Q1 2013.

  19. What determines the direction of subliminal priming

    PubMed Central

    Jaśkowski, Piotr; Verleger, Rolf

    2008-01-01

    Masked stimuli (primes) can affect the preparation of a motor response to subsequently presented target stimuli. Reactions to the target can be facilitated (straight priming) or inhibited (inverse priming) when preceded by a compatible prime (calling for the same response) and also when preceded by an incompatible prime. Several hypotheses are currently under debate. These are the self-inhibition (SI) hypothesis, the object-updating (OU) hypothesis, and mask-triggered inhibition (MTI) hypothesis. All assume that the initial activation of the motor response is elicited by the prime according to its identity. This activation inevitably leads to straight priming in some cases and the mechanisms involved are undisputed. The hypotheses differ, however, as to why inverse priming occurs. The self-inhibition (SI) hypothesis assumes that the motor activation elicited by a prime is automatically followed by an inhibition phase, leading to inverse priming if three conditions are fulfilled: perceptual evidence for the prime has to be sufficiently strong, it has to be immediately removed by the mask, and the delay between the prime and target has to be long enough for inhibition to become effective. The object-updating (OU) hypothesis assumes that inverse priming is triggered by the mask, provided that it contains features calling for the alternative response (i.e. the one contrasting with the response induced by the prime). The MTI hypothesis assumes that the inhibitory phase is triggered by each successive stimulus which does not support the perceptual hypothesis provided by the prime. Based mostly on our own experiments, we argue that (1) attempts to manipulate the three factors required by the SI hypothesis imply changes of other variables and that (2) indeed, other variables seem to affect priming: prime-mask perceptual interaction and temporal position of the mask. These observations are in favor of the MTI hypothesis. A limiting factor for all three hypotheses is that

  20. Wafer-scale epitaxial lift-off of optoelectronic grade GaN from a GaN substrate using a sacrificial ZnO interlayer

    NASA Astrophysics Data System (ADS)

    Rajan, Akhil; Rogers, David J.; Ton-That, Cuong; Zhu, Liangchen; Phillips, Matthew R.; Sundaram, Suresh; Gautier, Simon; Moudakir, Tarik; El-Gmili, Youssef; Ougazzaden, Abdallah; Sandana, Vinod E.; Teherani, Ferechteh H.; Bove, Philippe; Prior, Kevin A.; Djebbour, Zakaria; McClintock, Ryan; Razeghi, Manijeh

    2016-08-01

    Full 2 inch GaN epilayers were lifted off GaN and c-sapphire substrates by preferential chemical dissolution of sacrificial ZnO underlayers. Modification of the standard epitaxial lift-off (ELO) process by supporting the wax host with a glass substrate proved key in enabling full wafer scale-up. Scanning electron microscopy and x-ray diffraction confirmed that intact epitaxial GaN had been transferred to the glass host. Depth-resolved cathodoluminescence (CL) analysis of the bottom surface of the lifted-off GaN layer revealed strong near-band-edge (3.33 eV) emission indicating a superior optical quality for the GaN which was lifted off the GaN substrate. This modified ELO approach demonstrates that previous theories proposing that wax host curling was necessary to keep the ELO etch channel open do not apply to the GaN/ZnO system. The unprecedented full wafer transfer of epitaxial GaN to an alternative support by ELO offers the perspective of accelerating industrial adoption of the expensive GaN substrate through cost-reducing recycling.

  1. Relational integrativity of prime-target pairs moderates congruity effects in evaluative priming.

    PubMed

    Ihmels, Max; Freytag, Peter; Fiedler, Klaus; Alexopoulos, Theodore

    2016-05-01

    In evaluative priming, positive or negative primes facilitate reactions to targets that share the same valence. While this effect is commonly explained as reflecting invariant structures in semantic long-term memory or in the sensorimotor system, the present research highlights the role of integrativity in evaluative priming. Integrativity refers to the ease of integrating two concepts into a new meaningful compound representation. In extended material tests using paired comparisons from two pools of positive and negative words, we show that evaluative congruity is highly correlated with integrativity. Therefore, in most priming studies, congruity and integrativity are strongly confounded. When both aspects are disentangled by manipulating congruity and integrativity orthogonally, three priming experiments show that evaluative-priming effects were confined to integrative prime-target pairs. No facilitation of prime-congruent targets was obtained for non-integrative stimuli. These findings are discussed from a broader perspective on priming conceived as flexible, context-dependent, and serving a generative adaptation function.

  2. Atomic-Level Study of Melting Behavior of GaN Nanotubes

    SciTech Connect

    Wang, Zhiguo; Zu, Xiaotao; Gao, Fei; Weber, William J.

    2006-09-20

    Molecular dynamics simulations with a Stillinger-Weber potential have been used to investigate the melting behavior of wurtzite-type single crystalline GaN nanotubes. The simulations show that the melting temperature of GaN nanotubes is much lower than that of bulk GaN, which may be associated with the large surface-to-volume ratio of the nanotubes. The melting temperature of the GaN nanotubes increases with the thickness of the nanotubes to a saturation value, which is close to the melting temperature of a GaN slab. The results reveal that the nanotubes begin to melt at the surface, and then the melting rapidly extends to the interior of the nanotubes as the temperature increases. The melting temperature of a single-crystalline GaN nanotube with [100]-oriented lateral facets is higher than that with [110]-oriented lateral facets for the same thickness.

  3. Photo-induced Doping in GaN Epilayers with Graphene Quantum Dots

    PubMed Central

    Lin, T. N.; Inciong, M. R.; Santiago, S. R. M. S.; Yeh, T. W.; Yang, W. Y.; Yuan, C. T.; Shen, J. L.; Kuo, H. C.; Chiu, C. H.

    2016-01-01

    We demonstrate a new doping scheme where photo-induced carriers from graphene quantum dots (GQDs) can be injected into GaN and greatly enhance photoluminescence (PL) in GaN epilayers. An 8.3-fold enhancement of PL in GaN is observed after the doping. On the basis of time-resolved PL studies, the PL enhancement is attributed to the carrier transfer from GQDs to GaN. Such a carrier transfer process is caused by the work function difference between GQDs and GaN, which is verified by Kelvin probe measurements. We have also observed that photocurrent in GaN can be enhanced by 23-fold due to photo-induced doping with GQDs. The improved optical and transport properties from photo-induced doping are promising for applications in GaN-based optoelectronic devices. PMID:26987403

  4. Fabrication and characterization of GaN nanowire doubly clamped resonators

    SciTech Connect

    Maliakkal, Carina B. Mathew, John P.; Hatui, Nirupam; Rahman, A. Azizur; Deshmukh, Mandar M.; Bhattacharya, Arnab

    2015-09-21

    Gallium nitride (GaN) nanowires (NWs) have been intensely researched as building blocks for nanoscale electronic and photonic device applications; however, the mechanical properties of GaN nanostructures have not been explored in detail. The rigidity, thermal stability, and piezoelectric properties of GaN make it an interesting candidate for nano-electromechanical systems. We have fabricated doubly clamped GaN NW electromechanical resonators on sapphire using electron beam lithography and estimated the Young's modulus of GaN from resonance frequency measurements. For wires of triangular cross section with side ∼90 nm, we obtained values for the Young's modulus to be about 218 and 691 GPa, which are of the same order of magnitude as the values reported for bulk GaN. We also discuss the role of residual strain in the nanowire on the resonant frequency and the orientation dependence of the Young's modulus in wurtzite crystals.

  5. Graphene oxide assisted synthesis of GaN nanostructures for reducing cell adhesion.

    PubMed

    Yang, Rong; Zhang, Ying; Li, Jingying; Han, Qiusen; Zhang, Wei; Lu, Chao; Yang, Yanlian; Dong, Hongwei; Wang, Chen

    2013-11-21

    We report a general approach for the synthesis of large-scale gallium nitride (GaN) nanostructures by the graphene oxide (GO) assisted chemical vapor deposition (CVD) method. A modulation effect of GaN nanostructures on cell adhesion has been observed. The morphology of the GaN surface can be controlled by GO concentrations. This approach, which is based on the predictable choice of the ratio of GO to catalysts, can be readily extended to the synthesis of other materials with controllable nanostructures. Cell studies show that GaN nanostructures reduced cell adhesion significantly compared to GaN flat surfaces. The cell-repelling property is related to the nanostructure and surface wettability. These observations of the modulation effect on cell behaviors suggest new opportunities for novel GaN nanomaterial-based biomedical devices. We believe that potential applications will emerge in the biomedical and biotechnological fields.

  6. Microbial stress priming: a meta-analysis.

    PubMed

    Andrade-Linares, Diana R; Lehmann, Anika; Rillig, Matthias C

    2016-04-01

    Microbes have to cope with complex and dynamic environments, making it likely that anticipatory responses provide fitness benefits. Mild, previous stressors can prepare microbes (stress priming) to further and potentially damaging stressors (triggering). We here quantitatively summarize the findings from over 250 trials of 34 studies including bacteria and fungi, demonstrating that priming to stress has a beneficial impact on microbial survival. In fact, survival of primed microbes was about 10-fold higher compared with that in non-primed microbes. Categorical moderators related to microbial taxonomy and the kind of stress applied as priming or as triggering revealed significant differences of priming effect size among 14 different microbial species, 6 stress categories and stressor combination. We found that priming by osmotic, physiological and temperature stress had the highest positive effect sizes on microbial response. Cross-protection was evident for physiological, temperature and pH stresses. Microbes are better prepared against triggering by oxidative, temperature and osmotic stress. Our finding of an overall positive mean effect of priming regardless of the microbial system and particular stressor provides unprecedentedly strong evidence of the broad ecological significance of microbial stress priming. These results further suggest that stress priming may be an important factor in shaping microbial communities.

  7. Wrath of God: religious primes and punishment.

    PubMed

    McKay, Ryan; Efferson, Charles; Whitehouse, Harvey; Fehr, Ernst

    2011-06-22

    Recent evidence indicates that priming participants with religious concepts promotes prosocial sharing behaviour. In the present study, we investigated whether religious priming also promotes the costly punishment of unfair behaviour. A total of 304 participants played a punishment game. Before the punishment stage began, participants were subliminally primed with religion primes, secular punishment primes or control primes. We found that religious primes strongly increased the costly punishment of unfair behaviours for a subset of our participants--those who had previously donated to a religious organization. We discuss two proximate mechanisms potentially underpinning this effect. The first is a 'supernatural watcher' mechanism, whereby religious participants punish unfair behaviours when primed because they sense that not doing so will enrage or disappoint an observing supernatural agent. The second is a 'behavioural priming' mechanism, whereby religious primes activate cultural norms pertaining to fairness and its enforcement and occasion behaviour consistent with those norms. We conclude that our results are consistent with dual inheritance proposals about religion and cooperation, whereby religions harness the byproducts of genetically inherited cognitive mechanisms in ways that enhance the survival prospects of their adherents.

  8. The temporal dynamics of visual object priming.

    PubMed

    Ko, Philip C; Duda, Bryant; Hussey, Erin P; Mason, Emily J; Ally, Brandon A

    2014-11-01

    Priming reflects an important means of learning that is mediated by implicit memory. Importantly, priming occurs for previously viewed objects (item-specific priming) and their category relatives (category-wide priming). Two distinct neural mechanisms are known to mediate priming, including the sharpening of a neural object representation and the retrieval of stimulus-response mappings. Here, we investigated whether the relationship between these neural mechanisms could help explain why item-specific priming generates faster responses than category-wide priming. Participants studied pictures of everyday objects, and then performed a difficult picture identification task while we recorded event-related potentials (ERP). The identification task gradually revealed random line segments of previously viewed items (Studied), category exemplars of previously viewed items (Exemplar), and items that were not previously viewed (Unstudied). Studied items were identified sooner than Unstudied items, showing evidence of item-specific priming, and importantly Exemplar items were also identified sooner than Unstudied items, showing evidence of category-wide priming. Early activity showed sustained neural suppression of parietal activity for both types of priming. However, these neural suppression effects may have stemmed from distinct processes because while category-wide neural suppression was correlated with priming behavior, item-specific neural suppression was not. Late activity, examined with response-locked ERPs, showed additional processes related to item-specific priming including neural suppression in occipital areas and parietal activity that was correlated with behavior. Together, we conclude that item-specific and category-wide priming are mediated by separate, parallel neural mechanisms in the context of the current paradigm. Temporal differences in behavior are determined by the timecourses of these distinct processes.

  9. Radiation effects in GaN devices and materials (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Sun, Ke-Xun; Nelson, Ron; Yeamans, Charles

    2016-10-01

    Gallium Nitride (GaN) is a wide-bandgap semiconductor having excellent radiation properties. GaN crystal is ionic-covalent with significant iconicity resulting in stronger molecular bond strength, which in in turn leads to excellent radiation hardness. Further, GaN has ultrafast carrier relaxation time. GaN transistors are promising for high-frequency applications due to their large bandgap (3.9eV) and higher breakdown field (<5MV/cm). These exceptional characteristics make GaN suitable to operate in high radiation flux environment such as fusion plasma facilities, for ultrafast detection. The expected detector temporal response is faster than 0.01-1 ns. We have been systematically testing neutron radiation effects in GaN devices and materials at Los Alamos Neutron Science Center (LANSCE) with ever increased neutron fluence levels, and at National Ignition Facility (NIF) high foot, high yield shots. In 2013 LANSCE run cycle, we tested GaN UV LED devices at 3.1E11 neutrons/cm^2. In 2015-2016 LANSCE run cycles, we have been operating three neutron beam lines with fluence level 1.2E11, 1.5E13, and 1E15 neutrons/cm^2. The irradiated samples include GaN UV LEDs, GaN HEMTs, and GaN substrates. In the experiments up to 2015 run cycle, we have characterized electrical and optical performances of GaN device before and after neutron irradiation, including the device IV curve measurements monitored at over the three months neutron irradiation time, and device IV curve measurements before and after NIF high yield shot irradiation. We observed no substantial degradation. These experiments firmly established GaN devices as the radiation hard platform of the next generation fusion plasma diagnostic instruments.

  10. DDT_thmuelle_5: Herschel's first observation of a potentially hazardous object: 2005 YU55

    NASA Astrophysics Data System (ADS)

    Müeller, T.

    2011-10-01

    We propose to observe the Apollo- and C-type asteroid 2005 YU55, which is on a Mars-Earth-Venus crossing orbit, during its upcoming exceptional Earth approach. In November 2011 it will pass within 0.85 lunar distances (0.85 LD) of the Earth, during which it will have a brief (less than one OD) observing window for Herschel. No asteroid of that size has ever been observed to pass inside 1 LD (and it will not happen again before 2028) although, according to recent orbit simulations, it does not pose any risk of an impact with Earth for the next 100 years. The proposed 0.3 hours of Herschel-PACS observations will allow us to characterize the object's size and its albedo. In combination with the foreseen radar measurements we will also be able to derive thermal surface properties which are strongly influencing non-gravitational forces, considered as one of the reasons for the large uncertainties in long-term orbit studies.

  11. Barotropic processes associated with the development of the Mei-yu precipitation system

    NASA Astrophysics Data System (ADS)

    Li, Tingting; Li, Xiaofan

    2016-05-01

    The barotropic processes associated with the development of a precipitation system are investigated through analysis of cloud-resolving model simulations of Mei-yu torrential rainfall events over eastern China in mid-June 2011. During the model integration period, there were three major heavy rainfall events: 9-12, 13-16 and 16-20 June. The kinetic energy is converted from perturbation to mean circulations in the first and second period, whereas it is converted from mean to perturbation circulations in the third period. Further analysis shows that kinetic energy conversion is determined by vertical transport of zonal momentum. Thus, the prognostic equation of vertical transport of zonal momentum is derived, in which its tendency is associated with dynamic, pressure gradient and buoyancy processes. The kinetic energy conversion from perturbation to mean circulations in the first period is mainly associated with the dynamic processes. The kinetic energy conversion from mean to perturbation circulations in the third period is generally related to the pressure gradient processes.

  12. Spontaneous nucleation and growth of GaN nanowires: the fundamental role of crystal polarity.

    PubMed

    Fernández-Garrido, Sergio; Kong, Xiang; Gotschke, Tobias; Calarco, Raffaella; Geelhaar, Lutz; Trampert, Achim; Brandt, Oliver

    2012-12-12

    We experimentally investigate whether crystal polarity affects the growth of GaN nanowires in plasma-assisted molecular beam epitaxy and whether their formation has to be induced by defects. For this purpose, we prepare smooth and coherently strained AlN layers on 6H-SiC(0001) and SiC(0001̅) substrates to ensure a well-defined polarity and an absence of structural and morphological defects. On N-polar AlN, a homogeneous and dense N-polar GaN nanowire array forms, evidencing that GaN nanowires form spontaneously in the absence of defects. On Al-polar AlN, we do not observe the formation of Ga-polar GaN NWs. Instead, sparse N-polar GaN nanowires grow embedded in a Ga-polar GaN layer. These N-polar GaN nanowires are shown to be accidental in that the necessary polarity inversion is induced by the formation of Si(x)N. The present findings thus demonstrate that spontaneously formed GaN nanowires are irrevocably N-polar. Due to the strong impact of the polarity on the properties of GaN-based devices, these results are not only essential to understand the spontaneous formation of GaN nanowires but also of high technological relevance.

  13. Si in GaN -- On the nature of the background donor

    SciTech Connect

    Wetzel, C.; Chen, A.L.; Suski, T.; Ager, J.W. III; Walukiewicz, W.

    1996-08-01

    A characterization of the Si impurity in GaN is performed by Raman spectroscopy. Applying hydrostatic pressure up to 25 GPa the authors study the behavior of the LO phonon-plasmon mode in a series of high mobility Si doped GaN films. In contrast to earlier results on unintentionally doped bulk GaN crystals no freeze out of the free carriers could be observed in Si doped samples. The authors find that Si is a shallow hydrogenic donor throughout the pressure range studied. This result positively excludes Si incorporation as a dominant source of free electrons in previously studied bulk GaN samples.

  14. Growth and properties of bulk single crystals of GaN

    SciTech Connect

    Suski, T.; Perlin, P.; Leszczynski, M.

    1996-11-01

    In this paper the authors review recent developments in the growth of bulk GaN crystals by a high-pressure, high-temperature method. They also provide information on various physical properties of bulk GaN material. Then, some preliminary results on the homoepitaxial growth of GaN are given. In the second part of this paper the authors discuss the following problems: the possible origin of the large free electron concentration in undoped GaN material, the parasitic effect of yellow luminescence and the nature of Zn- and Mg-acceptors.

  15. Fabrication of a Lateral Polarity GaN MESFET: An Exploratory Study

    DTIC Science & Technology

    2007-06-27

    the sheet resistance between Ga- polar and mixed-polar GaN films. Highly resistive Ga-polar GaN is advantageous in optoelectronic and electronic device...re si st an ce [ M Ω /s q. ] 108642 2nd nitridation time [min] (b) Figure 5. Sheet resistance of GaN grown on AlN region for the first set of LT...AlN layers deposited for 4, 6, and 8 min. 2nd nitridation time after ex-situ process was kept at 950°C for 1 min. (b) Sheet resistance of GaN grown on

  16. Homoepitaxial growth of catalyst-free GaN wires on N-polar substrates

    NASA Astrophysics Data System (ADS)

    Chen, X. J.; Perillat-Merceroz, G.; Sam-Giao, D.; Durand, C.; Eymery, J.

    2010-10-01

    The shape of c-oriented GaN nanostructures is found to be directly related to the crystal polarity. As evidenced by convergent beam electron diffraction applied to GaN nanostructures grown by metal-organic vapor phase epitaxy on c-sapphire substrates: wires grown on nitridated sapphire have the N-polarity ([0001¯]) whereas pyramidal crystals have Ga-polarity ([0001]). In the case of homoepitaxy, the GaN wires can be directly selected using N-polar GaN freestanding substrates and exhibit good optical properties. A schematic representation of the kinetic Wulff's plot points out the effect of surface polarity.

  17. Structural defects in GaN revealed by Transmission Electron Microscopy

    DOE PAGES

    Liliental-Weber, Zuzanna

    2014-09-08

    This paper reviews the various types of structural defects observed by Transmission Electron Microscopy in GaN heteroepitaxial layers grown on foreign substrates and homoepitaxial layers grown on bulk GaN substrates. The structural perfection of these layers is compared to the platelet self-standing crystals grown by High Nitrogen Pressure Solution. Defects in undoped and Mg doped GaN are discussed. Lastly, some models explaining the formation of inversion domains in heavily Mg doped layers that are possible defects responsible for the difficulties of p-doping in GaN are also reviewed.

  18. Characterizations of GaN film growth by ECR plasma chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Fu, Silie; Chen, Junfang; Zhang, Hongbin; Guo, Chaofen; Li, Wei; Zhao, Wenfen

    2009-06-01

    The electron cyclotron resonance plasma-enhanced metalorganic chemical vapor deposition technology (ECR-MOPECVD) is adopted to grow GaN films on (0 0 0 1) α-Al2O3 substrate. The gas sources are pure N2 and trimethylgallium (TMG). Optical emission spectroscopy (OES) and thermodynamic analysis of GaN growth are applied to understand the GaN growth process. The OES of ECR plasma shows that TMG is significantly dissociated in ECR plasma. Reactants N and Ga in the plasma, obtained easily under the self-heating condition, are essential for the GaN growth. They contribute to the realization of GaN film growth at a relatively low temperature. The thermodynamic study shows that the driving force for the GaN growth is high when N2:TMG>1. Furthermore, higher N2:TMG flow ratio makes the GaN growth easier. Finally, X-ray diffraction, photoluminescence, and atomic force microscope are applied to investigate crystal quality, morphology, and roughness of the GaN films. The results demonstrate that the ECR-MOPECVD technology is favorable for depositing GaN films at low temperatures.

  19. Optical and field emission properties of layer-structure GaN nanowires

    SciTech Connect

    Cui, Zhen; Li, Enling; Shi, Wei; Ma, Deming

    2014-08-15

    Highlights: • The layer-structure GaN nanowires with hexagonal-shaped cross-sections are produced via a process based on the CVD method. • The diameter of the layer-structure GaN nanowire gradually decreases from ∼500 nm to ∼200 nm along the wire axis. • The layer-structure GaN nanowire film possesses good field emission property. - Abstract: A layer-structure gallium nitride (GaN) nanowires, grown on Pt-coated n-type Si (1 1 1) substrate, have been synthesized using chemical vapor deposition (CVD). The results show: (1) SEM indicates that the geometry structure is layer-structure. HRTEM indicates that GaN nanowire’s preferential growth direction is along [0 0 1] direction. (2) The room temperature PL emission spectrum of the layer-structure GaN nanowires has a peak at 375 nm, which proves that GaN nanowires have potential application in light-emitting nano-devices. (3) Field-emission measurements show that the layer-structure GaN nanowires film has a low turn-on field of 4.39 V/μm (at room temperature), which is sufficient for electron emission devices, field emission displays and vacuum nano-electronic devices. The growth mechanism for GaN nanowires has also been discussed briefly.

  20. Demonstration of flexible thin film transistors with GaN channels

    NASA Astrophysics Data System (ADS)

    Bolat, S.; Sisman, Z.; Okyay, A. K.

    2016-12-01

    We report on the thin film transistors (TFTs) with Gallium Nitride (GaN) channels directly fabricated on flexible substrates. GaN thin films are grown by hollow cathode plasma assisted atomic layer deposition (HCPA-ALD) at 200 °C. TFTs exhibit 103 on-to-off current ratios and are shown to exhibit proper transistor saturation behavior in their output characteristics. Gate bias stress tests reveal that flexible GaN TFTs have extremely stable electrical characteristics. Overall fabrication thermal budget is below 200 °C, the lowest reported for the GaN based transistors so far.

  1. On Anti-Elite Prime Numbers

    NASA Astrophysics Data System (ADS)

    M"Uller, Tom

    2007-09-01

    An odd prime number p is called anti-elite if only finitely many Fermat numbers are quadratic non-residues to p. This concept is the exact opposite to that of elite prime numbers. We study some fundamental properties of anti-elites and show that there are infinitely many of them. A computational search among all the numbers up to 100 billion yielded 84 anti-elite primes.

  2. All Elite Primes Up to 250 Billion

    NASA Astrophysics Data System (ADS)

    Chaumont, Alain; Müller, Tom

    2006-08-01

    A prime number p is called elite if only finitely many Fermat numbers 2^(2^n)+1 are quadratic residues of p. Previously only the interval up to 10^9 was systematically searched for elite primes and 16 such primes were found. We extended this research up to 2.5*10^11 and found five further elites, among which 1,151,139,841 is the smallest and 171,727,482,881 the largest.

  3. Improved photoelectrochemical performance of GaN nanopillar photoanodes.

    PubMed

    Narangari, Parvathala Reddy; Karuturi, Siva Krishna; Lysevych, Mykhaylo; Hoe Tan, Hark; Jagadish, Chennupati

    2017-04-18

    In this work, we report on the photoelectrochemical (PEC) investigation of n-GaN nanopillar (NP) photoanodes fabricated using metal organic chemical vapour deposition and the top-down approach. Substantial improvement in photocurrents is observed for GaN NP photoanodes compared to their planar counterparts. The role of carrier concentration and NP dimensions on the PEC performance of NP photoanodes is further elucidated. Photocurrent density is almost doubled for doped NP photoanodes whereas no improvement is noticed for undoped NP photoanodes. While the diameter of GaN NP is found to influence the onset potential, carrier concentration is found to affect both the onset and overpotential of the electrodes. Optical and electrochemical impedance spectroscopy characterisations are utilised to further explain the PEC results of NP photoanodes. Finally, improvement in the photostability of NP photoanodes with the addition of NiO as a co-catalyst is investigated.

  4. Size dictated thermal conductivity of GaN

    SciTech Connect

    Thomas Edwin Beechem; McDonald, Anthony E.; Fuller, Elliot James; Talin, Albert Alec; Rost, Christina M.; Maria, Jon -Paul; Gaskins, John T.; Hopkins, Patrick E.; Allerman, Andrew A.

    2016-04-01

    The thermal conductivity on n- and p-type doped gallium nitride (GaN) epilayers having thickness of 3-4 μm was investigated using time domain thermoreflectance (TDTR). Despite possessing carrier concentrations ranging across 3 decades (1015 – 1018 cm–3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends–and their overall reduction relative to bulk–are explained leveraging established scattering models where it is shown that size effects play a primary role in limiting thermal conductivity for layers even tens of microns thick. GaN device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness.

  5. Selective excitation of the yellow luminescence of GaN

    SciTech Connect

    Colton, J.S.; Yu, P.Y.; Teo, K.L.; Weber, E.R.; Grzegory, I.; Uchida, K.

    1999-07-01

    The yellow luminescence of n-type GaN has been studied with selective excitation using a combination of Ar ion and dye lasers. Narrower structures whose peak energies follow the excitation photon energy over the width of the yellow luminescence have been observed. Unlike the yellow luminescence excited by above band gap excitations, these fine structures exhibits thermal activated quenching behavior. We propose that these fine structures are due to emission occurring at complexes of shallow donors and deep acceptors which can be resonantly excited by photons with energies below the band gap. The activation energy deduced from their intensity is that for delocalization of electrons out of the complexes. Our results therefore suggest that there is more than one recombination channel (usually assumed to be due to distant donor-acceptor pairs) to the yellow luminescence in GaN.

  6. Improved photoelectrochemical performance of GaN nanopillar photoanodes

    NASA Astrophysics Data System (ADS)

    Reddy Narangari, Parvathala; Krishna Karuturi, Siva; Lysevych, Mykhaylo; Tan, Hark Hoe; Jagadish, Chennupati

    2017-04-01

    In this work, we report on the photoelectrochemical (PEC) investigation of n-GaN nanopillar (NP) photoanodes fabricated using metal organic chemical vapour deposition and the top-down approach. Substantial improvement in photocurrents is observed for GaN NP photoanodes compared to their planar counterparts. The role of carrier concentration and NP dimensions on the PEC performance of NP photoanodes is further elucidated. Photocurrent density is almost doubled for doped NP photoanodes whereas no improvement is noticed for undoped NP photoanodes. While the diameter of GaN NP is found to influence the onset potential, carrier concentration is found to affect both the onset and overpotential of the electrodes. Optical and electrochemical impedance spectroscopy characterisations are utilised to further explain the PEC results of NP photoanodes. Finally, improvement in the photostability of NP photoanodes with the addition of NiO as a co-catalyst is investigated.

  7. Prime Graph Components of Finite Simple Groups

    NASA Astrophysics Data System (ADS)

    Kondrat'ev, A. S.

    1990-02-01

    Let G be a finite group and π(G) the set of prime factors of its order. The prime graph of G is the graph with vertex-set π(G), two vertices p and q being joined by an edge whenever G contains an element of order pq. This article contains an explicit description of the primes in each of the connected components of the prime graphs of the finite simple groups of Lie type of even characteristic. This solves question 9.16 of the Kourovka Notebook. Bibliography: 15 titles.

  8. Erbium Doped GaN Lasers by Optical Pumping

    DTIC Science & Technology

    2016-07-13

    P.O. Box 12211 Research Triangle Park, NC 27709-2211 Er doped GaN, gain medium, high energy laser, optical pump REPORT DOCUMENTATION PAGE 11. SPONSOR...Nanophotonics Center, Texas Tech University Lubbock, TX 79409-3102 jingyu.lin@ttu.edu; hx.jiang@ttu.edu I. Summary of Progress High energy and...emerging technologies. The optical gain medium is the heart of a high energy laser (HEL) system. Comparing with the presently dominant gain material

  9. Priming effects in marine sediments

    NASA Astrophysics Data System (ADS)

    Gontikaki, Evina; Thornton, Barry; Witte, Ursula

    2013-04-01

    Continental margin sediments (<2000 m) cover merely 15 % of the ocean's seafloor but are responsible for more than 70 % of the global benthic mineralization. Understanding when these systems act as a source or sink of carbon (C) is thus of primary importance if we are to produce reliable global C budgets and predict the effects of future perturbations on the global C cycle. The chemical nature of organic matter (OM) is thought to be one of the major controls on the degradation/preservation balance in sediments; labile and refractory OM pools degrade at different rates but not independently. Priming effects (PE), i.e. changes in the decomposition of refractory organic matter following inputs of labile OM, have the potential to alter the C budget in sediments but have been largely ignored by marine scientists. Climate-driven changes in primary production, and land erosion and run-off are likely to change the quantity and composition of organic matter inputs in marine ecosystems and influence the magnitude and direction of PEs in seawater and sediments. Here, we attempt to evaluate the importance of priming effects on C cycling in marine sediments by use of labelled substrates of different quantity and quality in stable isotope tracer experiments and argue that PEs need to be incorporated in global change models.

  10. MgCaO Dry Etching on GaN

    NASA Astrophysics Data System (ADS)

    Hlad, M.; Ren, F.

    2005-11-01

    MgCaO films grown by rf plasma-assisted Molecular Beam Epitaxy and capped with Sc2O3 are promising candidates as surface passivation layers and gate dielectrics on GaN-based high electron mobility transistors (HEMTs) and metal-oxide semiconductor HEMTs (MOS-HEMTs) respectively. Two different plasma chemistries were examined for etching these thin films on GaN. Inductively Coupled Plasmas of CH4/H2/Ar produced etch rates only in the range 20-70 å/min, comparable to the Ar sputter rates under the same conditions. Similarly slow MgCaO etch rates (˜100 å/min) were obtained with Cl2/Ar discharges under the same conditions, but GaN showed rates almost an order of magnitude higher. The MgCaO removal rates are limited by the low volatilities of the respective etch products. The CH4/H2/Ar plasma chemistry produced a selectivity of around 2 or etching the MgCaO with respect to GaN.

  11. Epitaxially-Grown GaN Junction Field Effect Transistors

    SciTech Connect

    Baca, A.G.; Chang, P.C.; Denbaars, S.P.; Lester, L.F.; Mishra, U.K.; Shul, R.J.; Willison, C.G.; Zhang, L.; Zolper, J.C.

    1999-05-19

    Junction field effect transistors (JFET) are fabricated on a GaN epitaxial structure grown by metal organic chemical vapor deposition (MOCVD). The DC and microwave characteristics of the device are presented. A junction breakdown voltage of 56 V is obtained corresponding to the theoretical limit of the breakdown field in GaN for the doping levels used. A maximum extrinsic transconductance (gm) of 48 mS/mm and a maximum source-drain current of 270 mA/mm are achieved on a 0.8 µ m gate JFET device at VGS= 1 V and VDS=15 V. The intrinsic transconductance, calculated from the measured gm and the source series resistance, is 81 mS/mm. The fT and fmax for these devices are 6 GHz and 12 GHz, respectively. These JFETs exhibit a significant current reduction after a high drain bias is applied, which is attributed to a partially depleted channel caused by trapped hot-electrons in the semi-insulating GaN buffer layer. A theoretical model describing the current collapse is described, and an estimate for the length of the trapped electron region is given.

  12. Metal contacts on ZnSe and GaN

    SciTech Connect

    Duxstad, Kristin Joy

    1997-05-01

    Recently, considerable interest has been focused on the development of blue light emitting materials and devices. The focus has been on GaN and ZnSe, direct band gap semiconductors with bands gaps of 3.4 and 2.6 eV, respectively. To have efficient, reliable devices it is necessary to have thermally and electrically stable Ohmic contacts. This requires knowledge of the metal-semiconductor reaction behavior. To date few studies have investigated this behavior. Much information has accumulated over the years on the behavior of metals on Si and GaAs. This thesis provides new knowledge for the more ionic wide band gap semiconductors. The initial reaction temperatures, first phases formed, and phase stability of Pt, Pd, and Ni on both semiconductors were investigated. The reactions of these metals on ZnSe and GaN are discussed in detail and correlated with predicted behavior. In addition, comparisons are made between these highly ionic semiconductors and Si and GaAs. The trends observed here should also be applicable to other II-VI and III-Nitride semiconductor systems, while the information on phase formation and stability should be useful in the development of contacts for ZnSe and GaN devices.

  13. Study of neutron irradiated structures of ammonothermal GaN

    NASA Astrophysics Data System (ADS)

    Gaubas, E.; Ceponis, T.; Deveikis, L.; Meskauskaite, D.; Miasojedovas, S.; Mickevicius, J.; Pavlov, J.; Pukas, K.; Vaitkus, J.; Velicka, M.; Zajac, M.; Kucharski, R.

    2017-04-01

    Study of the radiation damage in GaN-based materials becomes an important aspect for possible application of the GaN detectors in the harsh radiation environment at the Large Hadron Collider and at other particle acceleration facilities. Intentionally doped and semi-insulating bulk ammonothermal GaN materials were studied to reveal the dominant defects introduced by reactor neutron irradiations. These radiation defects have been identified by combining electron spin resonance and transmission spectroscopy techniques. Characteristics of carrier lifetime dependence on neutron irradiation fluence were examined. Variations of the response of the capacitor-type sensors with neutron irradiation fluence have been correlated with the carrier lifetime changes. The measurements of the photoconductivity and photoluminescence transients have been used to study the variation of the parameters of radiative and non-radiative recombination. The examined characteristics indicate that AT GaN as a particle sensing material is radiation hard up to high hadron fluences  ⩾1016 cm‑2.

  14. Dislocation core structures in Si-doped GaN

    SciTech Connect

    Rhode, S. L. Fu, W. Y.; Sahonta, S.-L.; Kappers, M. J.; Humphreys, C. J.; Horton, M. K.; Pennycook, T. J.; Dusane, R. O.; Moram, M. A.

    2015-12-14

    Aberration-corrected scanning transmission electron microscopy was used to investigate the core structures of threading dislocations in plan-view geometry of GaN films with a range of Si-doping levels and dislocation densities ranging between (5 ± 1) × 10{sup 8} and (10 ± 1) × 10{sup 9} cm{sup −2}. All a-type (edge) dislocation core structures in all samples formed 5/7-atom ring core structures, whereas all (a + c)-type (mixed) dislocations formed either double 5/6-atom, dissociated 7/4/8/4/9-atom, or dissociated 7/4/8/4/8/4/9-atom core structures. This shows that Si-doping does not affect threading dislocation core structures in GaN. However, electron beam damage at 300 keV produces 4-atom ring structures for (a + c)-type cores in Si-doped GaN.

  15. Theoretical investigation of GaN carbon doped

    NASA Astrophysics Data System (ADS)

    Espitia Rico, M. J.; Moreno Armenta, M. G.; Rodríguez, J. A.; Takeuchi, N.

    2016-02-01

    In this work we used first principles calculations in the frame of density functional theory (DFT) in order to study the structural and electronic properties of GaN doped with carbon. The computational calculations were carried out by a method based on plane waves pseudopotentials, as implemented in the Quantum Espresso code. In the wurtzite type GaN supercell the nitrogen atoms were replaced by carbon atoms (C by N) and then also the gallium atoms by carbon atoms (C by Ga). The carbon concentrations in the GaN volume was set as x=25, 50 y 75%. For each concentration x of carbon the formation energy was calculated for the substitutions C by N and CxGa. We found that it is more energetically favourable that the carbon atoms occupy the positions of the nitrogen atoms (C by N), because in all the x concentrations of carbon the formation energies were lower than that in the substitutions (C by Ga). It was found that the new compounds CxGaN1-x have higher bulk moduli. So they are very rigid. This property makes them good candidates for applications in hard coatings or devices for high power and temperatures. Analysis of the density of states show that the new CxGaN1-x ternary compound have metallic behaviour that comes essentially from the hybridization states N-p and C-p cross the Fermi level.

  16. Theoretical and Experiment Study of Cathodoluminescence of GaN

    NASA Astrophysics Data System (ADS)

    Ben Nasr, F.; Matoussi, A.; Salh, R.; Boufaden, T.; Guermazi, S.; Fitting, H.-J.; Eljani, B.; Fakhfakh, Z.

    2007-09-01

    In this work, we report the theoretical and experimental results of cathodoluminescence (CL) from GaN layers with thickness (1-3) micron grown at 800 °C by MOVPE on silicon substrate. The CL measurements were performed in a digital scanning electron microscope DSM 960 at room temperature. The CL spectra recorded at room temperature (RT) show the main UV peak at 3.42 eV of the fundamental transition and a broad yellow band at 2.2 eV attributed the intrinsic defects and extrinsic dopants and impurities. The simulation of the CL excitation and intensity is developed using consistent 2-D model based on the electron beam energy dissipation and taking into account the effects of carrier diffusion, internal absorption and the recombination processes in GaN. Then, we have investigated the evolution of the CL intensity from GaN as a function the electron beam energy in the range Eo = (5-20) keV. A comparative study between experimental and simulated CL spectra at room temperature is presented.

  17. Nucleation conditions for catalyst-free GaN nanowires

    NASA Astrophysics Data System (ADS)

    Bertness, K. A.; Roshko, A.; Mansfield, L. M.; Harvey, T. E.; Sanford, N. A.

    2007-03-01

    We have examined the initial steps for catalyst-free growth of GaN nanowires by molecular beam epitaxy (MBE) on Si (1 1 1) substrates using AlN buffer layers. These wires form spontaneously under high N-to-Ga ratios for a growth temperature range of about 810-830 °C. Field emission scanning electron microscopy (FESEM) shows that part of the GaN forms a "matrix layer" that also grows with the [0 0 0 1] direction perpendicular to the substrate surface. This layer contains small, dense hexagonal pits in which the nanowires nucleate. Using both FESEM and atomic force microscopy (AFM), we identify the pit facets as {1 0 1¯ 2} planes. The nucleation studies show that the use of an AlN buffer layer is essential to the regular formation of the nanowires and matrix layers under our growth conditions. Our typical AlN buffer layer is 40-50 nm thick. We conclude that the nucleation mechanism for nanowires includes formation of nanocolumns in the AlN buffer layer. The propagation of the nanowires in GaN growth appears to be driven by differences in growth rates among crystallographic planes under N-rich conditions.

  18. Understanding the pyramidal growth of GaN

    SciTech Connect

    Rouviere, J.L.; Arlery, M.; Bourret, A.

    1996-11-01

    By a combination of conventional, HREM and CBED TEM experiments the authors have studied wurtzite GaN layers grown by Metal-Organic Chemical Vapor Deposition (MOCVD) on (0001)Al{sub 2}O{sub 3}. They experimentally determine the structure of the macroscopic hexagonal pyramids that are visible at the surface of the layers when no optimized buffer is introduced. These pyramids look like hexagonal volcanoes with one hexagonal microscopic chimney (up to 75 nm wide) at their core. The crystal inside the chimney is a pure GaN crystal with a polarity opposed to the one of the neighboring material: the GaN layers grown on (0001)Al{sub 2}O{sub 3} are everywhere Ga-terminated except in the chimneys where they are N-terminated. Some of the N-terminated chimneys grow faster and form macroscopic hexagonal pyramids. Chimneys bounded by Inversion Domains Boundaries (IDBs) originate from steps at the surface of the substrate and may be suppressed by an adapted buffer layer.

  19. Magnesium diffusion profile in GaN grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Benzarti, Z.; Halidou, I.; Bougrioua, Z.; Boufaden, T.; El Jani, B.

    2008-07-01

    The diffusion of magnesium has been studied in GaN layers grown on sapphire substrate by atmospheric pressure metalorganic vapor-phase-epitaxy (MOVPE) in a "home-made" reactor. Secondary Ion Mass Spectroscopy (SIMS) was used to visualise the Mg profiles in two kinds of multi-sublayer GaN structures. One structure was grown with a variable flow of Ga precursor (TMG) and the second one with a variable growth temperature. In both cases, the Mg dopant precursor (Cp 2Mg) flow was kept constant. Using the second Fick's law to fit the experimental SIMS data, we have deduced an increasing then a saturating Mg diffusion coefficient versus the Mg concentration. Mg incorporation was found to get higher for lower growth rate, i.e. when TMG flow is reduced. Furthermore, based on the temperature-related behaviour we have found that the activation energy for Mg diffusion coefficient in GaN was 1.9 eV. It is suggested that Mg diffuses via substitutional sites.

  20. Abnormal selective area growth of irregularly-shaped GaN structures on the apex of GaN pyramids and its application for wide spectral emission

    NASA Astrophysics Data System (ADS)

    Yu, Yeon Su; Lee, Jun Hyeong; Ahn, Hyung Soo; Yang, Min

    2014-12-01

    We report on the growth and the characterization of three-dimensional randomly-shaped InGaN/GaN structures selectively grown on the apex of GaN pyramids for the purpose of enlarging the emission spectral range. We found that the variations in the shape and the size of the three-dimensional GaN structures depend on the growth temperature and the surface area for selective growth under intentional turbulence in the gas stream. The selectively grown GaN structures grown at 1020 °C have irregular shape, while the samples grown at 1100 °C have rather uniform hexagonal pyramidal shapes. Irregularly shaped GaN structures were also obtained on the apex of GaN pyramids when the SiO2 mask was removed to 1/10 of the total height of the underlying GaN pyramid. When only 1/5 of the SiO2 mask was removed, however, the selectively grown GaN structures had similar hexagonal pyramidal shapes resembling those of the underlying GaN pyramids. The CL (Cathodoluminescence) spectra of the InGaN layers grown on the randomly shaped GaN structures showed a wide emission spectral range from 388 to 433 nm due to the non-uniform thickness and spatially inhomogeneous indium composition of the InGaN layers. This new selective growth method might have great potential for applications of non-phosphor white light emitting diodes (LEDs) with optimized growth conditions for InGaN active layers of high indium composition and with optimum process for fabrication of electrodes for electrical injection.

  1. Tight coupling between positive and reversed priming in the masked prime paradigm

    PubMed Central

    Boy, Frederic; Sumner, Petroc

    2011-01-01

    When associations between certain visual stimuli and particular actions are learnt, those stimuli become capable of automatically and unconsciously activating their associated action plans. Such sensorimotor priming is assumed to be fundamental for efficient responses, and can be reliably measured in masked prime studies even when the primes are not consciously perceived. However, when the delay between prime and target is increased, reversed priming effects are often found instead (the negative compatibility effect, NCE). The main accounts of the NCE assume that it too is a sensorimotor phenomenon, predicting that it should occur only when the initial positive priming phase also occurs. Alternatively, reversed priming may reflect a perceptual process entirely independent from positive motor priming (which is simply evident at a different temporal delay), in which case no dependency is expected between the NCE and positive priming. We tested these predictions while new sensorimotor associations were learnt, and when learnt associations were suddenly reversed. We found a remarkable symmetry between positive and reversed priming during all such learning phases, supporting the idea that reversed priming represents a sensorimotor process that is contingent on, and automatically follows, the positive priming phase. We discuss also whether the NCE mechanism is subject to a trigger threshold. PMID:20695707

  2. Longer prime presentation decreases picture-word cross-domain priming.

    PubMed

    Miyoshi, Kiyofumi; Kimura, Yusuke; Ashida, Hiroshi

    2015-01-01

    A short prime presentation has been shown to provide a greater priming magnitude, whereas a longer prime presentation results in a lower priming magnitude. In Experiment 1, we attempted to replicate the decrease of priming using word stimuli. Words were presented in both prime and test sessions, and participants judged whether each stimulus was natural or manmade. In Experiment 2, we employed a cross-domain priming paradigm to assess the impact of prime duration on non-perceptual processes. Pictures were presented in prime sessions, and their semantically matched words were presented in test sessions. We did not observe a significant decrease in priming in Experiment 1. However, we found that 2000 ms of prime exposure led to weaker cross-domain priming when compared with 250 ms of the exposure in Experiment 2. The results suggest that the longer presentation of pictures causes a non-perceptual adaptation effect. This effect may occur at conceptual, linguistic, and/or response-related levels.

  3. Unconscious congruency priming from unpracticed words is modulated by prime-target semantic relatedness.

    PubMed

    Ortells, Juan J; Marí-Beffa, Paloma; Plaza-Ayllón, Vanesa

    2013-03-01

    Participants performed a 2-choice categorization task on visible word targets that were preceded by novel (unpracticed) prime words. The prime words were presented for 33 ms and followed either immediately (Experiments 1-3) or after a variable delay (Experiments 1 and 4) by a pattern mask. Both subjective and objective measures of prime visibility were used in all experiments. On 80% of the trials the primes and targets belonged to different categories (incongruent trials), whereas in the remaining 20% (congruent trials) they could be either strong or weak semantically related category members. Positive congruency effects (reaction times faster on congruent than on incongruent trials) were consistently found, but only when the mask immediately followed the primes, and participants reported being unaware of the identity of the primes. Primes followed by a delayed mask (such that participants reported being aware of their identity) produced either nonreliable facilitation or reliable reversed priming (strategic), depending on whether the prime-target stimulus onset asynchrony was either short (200 ms; Experiments 1 and 4) or long (1,000 ms; Experiment 4). Facilitatory priming with immediate mask was found strong (a) even for participants who performed at chance in prime visibility tests; and (b) for high but not for weakly semantically related category coordinates, irrespective of category size (animals, body parts). These findings provide evidence that unconscious congruency priming by unpracticed words from large stimulus sets critically depends on associative strength and/or semantic similarity between category coexemplars.

  4. Comparative Transcriptional Profiling of Primed and Non-primed Rice Seedlings under Submergence Stress

    PubMed Central

    Hussain, Saddam; Yin, Hanqi; Peng, Shaobing; Khan, Faheem A.; Khan, Fahad; Sameeullah, Muhammad; Hussain, Hafiz A.; Huang, Jianliang; Cui, Kehui; Nie, Lixiao

    2016-01-01

    Submergence stress is a limiting factor for direct-seeded rice systems in rainfed lowlands and flood-prone areas of South and Southeast Asia. The present study demonstrated that submergence stress severely hampered the germination and seedling growth of rice, however, seed priming alleviated the detrimental effects of submergence stress. To elucidate the molecular basis of seed priming-induced submergence tolerance, transcriptome analyses were performed using 4-day-old primed (selenium-Se and salicylic acid-SA priming) and non-primed rice seedlings under submergence stress. Genomewide transcriptomic profiling identified 2371 and 2405 transcripts with Se- and SA-priming, respectively, that were differentially expressed in rice compared with non-priming treatment under submergence. Pathway and gene ontology term enrichment analyses revealed that genes involved in regulation of secondary metabolism, development, cell, transport, protein, and metal handling were over-represented after Se- or SA-priming. These coordinated factors might have enhanced the submergence tolerance and maintained the better germination and vigorous seedling growth of primed rice seedlings. It was also found that many genes involved in cellular and metabolic processes such as carbohydrate metabolism, cellular, and metabolic biosynthesis, nitrogen compound metabolic process, transcription, and response to oxidative stress were induced and overlapped in seed priming treatments, a finding which reveals the common mechanism of seed priming-induced submergence tolerance. Taken together, these results may provide new avenues for understanding and advancing priming-induced responses to submergence tolerance in crop plants. PMID:27516766

  5. The Effect of Prime Duration in Masked Orthographic Priming Depends on Neighborhood Distribution

    ERIC Educational Resources Information Center

    Robert, Christelle; Mathey, Stephanie

    2012-01-01

    A lexical decision task was used with a masked priming procedure to investigate whether and to what extent neighborhood distribution influences the effect of prime duration in masked orthographic priming. French word targets had two higher frequency neighbors that were either distributed over two letter positions (e.g., "LOBE/robe-loge")…

  6. Tight Coupling between Positive and Reversed Priming in the Masked Prime Paradigm

    ERIC Educational Resources Information Center

    Boy, Frederic; Sumner, Petroc

    2010-01-01

    When associations between certain visual stimuli and particular actions are learned, those stimuli become capable of automatically and unconsciously activating their associated action plans. Such sensorimotor priming is assumed to be fundamental for efficient responses, and can be reliably measured in masked prime studies even when the primes are…

  7. Unconscious Congruency Priming from Unpracticed Words Is Modulated by Prime-Target Semantic Relatedness

    ERIC Educational Resources Information Center

    Ortells, Juan J.; Mari-Beffa, Paloma; Plaza-Ayllon, Vanesa

    2013-01-01

    Participants performed a 2-choice categorization task on visible word targets that were preceded by novel (unpracticed) prime words. The prime words were presented for 33 ms and followed either immediately (Experiments 1-3) or after a variable delay (Experiments 1 and 4) by a pattern mask. Both subjective and objective measures of prime visibility…

  8. On the robustness of prime response retrieval processes: evidence from auditory negative priming without probe interference.

    PubMed

    Mayr, Susanne; Buchner, Axel

    2014-02-01

    Visual negative priming has been shown to depend on the presence of probe distractors, a finding that has been traditionally seen to support the episodic retrieval model of negative priming; however, facilitated prime-to-probe contingency learning might also underlie this effect. In four sound identification experiments, the role of probe distractor interference in auditory negative priming was investigated. In each experiment, a group of participants was exposed to probe distractor interference while another group ran the task in the absence of probe distractors. Experiments 1A, 1B, and 1C varied in the extent to which fast versus accurate responding was required. Between Experiments 1 and 2, the spatial cueing of the to-be-attended ear was varied. Whereas participants switched ears from prime to probe in Experiment 1, they kept a stable attentional focus throughout Experiment 2. For trials with probe distractors, a negative priming effect was present in all experiments. For trials without probe distractors, the only ubiquitous after-effect of ignoring a prime distractor was an increase of prime response errors in ignored repetition compared to control trials, indicating that prime response retrieval processes took place. Whether negative priming beyond this error increase was found depended on the stability of the attentional focus. The findings suggest that several mechanisms underlie auditory negative priming with the only robust one being prime response retrieval.

  9. Amount of Priming in the Difference of Mental Transformation

    ERIC Educational Resources Information Center

    Kanamori, Nobuhiro; Yagi, Akihiro

    2005-01-01

    We examined in detail effects of priming in 2 mental rotation strategies: spinning (rotating in a picture plane) and flipping (rotating in depth around a horizontal axis) by using a priming paradigm of Kanamori and Yagi (2002). The priming paradigm included prime and probe tasks within 1 trial. In the prime task, 16 participants were asked to…

  10. Inverse Target- and Cue-Priming Effects of Masked Stimuli

    ERIC Educational Resources Information Center

    Mattler, Uwe

    2007-01-01

    The processing of a visual target that follows a briefly presented prime stimulus can be facilitated if prime and target stimuli are similar. In contrast to these positive priming effects, inverse priming effects (or negative compatibility effects) have been found when a mask follows prime stimuli before the target stimulus is presented: Responses…

  11. A Paradox of Syntactic Priming: Why Response Tendencies Show Priming for Passives, and Response Latencies Show Priming for Actives

    PubMed Central

    Segaert, Katrien; Menenti, Laura; Weber, Kirsten; Hagoort, Peter

    2011-01-01

    Speakers tend to repeat syntactic structures across sentences, a phenomenon called syntactic priming. Although it has been suggested that repeating syntactic structures should result in speeded responses, previous research has focused on effects in response tendencies. We investigated syntactic priming effects simultaneously in response tendencies and response latencies for active and passive transitive sentences in a picture description task. In Experiment 1, there were priming effects in response tendencies for passives and in response latencies for actives. However, when participants' pre-existing preference for actives was altered in Experiment 2, syntactic priming occurred for both actives and passives in response tendencies as well as in response latencies. This is the first investigation of the effects of structure frequency on both response tendencies and latencies in syntactic priming. We discuss the implications of these data for current theories of syntactic processing. PMID:22022352

  12. One version of direct response priming requires automatization of the relevant associations but not awareness of the prime.

    PubMed

    Klapp, Stuart T

    2015-07-01

    Priming is the influence of one event on performance during a second event. One type of priming is known as semantic priming because it biases interpretation of the subsequent stimulus. Another type, direct response priming, biases responding directly without semantic mediation. Research reviewed in this article indicates that two versions of the second type, direct response priming, can be distinguished. One version, explicit priming, requires awareness of the prime. The other version, associative response priming, occurs even if the prime is masked and not phenomenally visible. This version, which is attributed to associations relating specific sensory events to movements of particular muscles, is enabled only if the association has previously been automatized by brief practice in which the to-be-primed response is made to the stimulus that subsequently appears as the prime. Associative response priming can be explained by a simple stimulus-response interpretation; other varieties of priming are more theoretically challenging.

  13. Multi-wavelength emitting InGan/GaN quantum well grown on V-shaped gan(1101) microfacet.

    PubMed

    Kang, Eun-Sil; Ju, Jin-Woo; Kim, Jin Soo; Ahn, Haeng-Keun; Lee, June Key; Kim, Jin Hyeok; Shin, Dong-Chan; Lee, In-Hwan

    2007-11-01

    InGaN/GaN multiple quantum wells (MQWs) were successfully grown on the inclined GaN(1101) microfacets. Conventional photolithography and subsequent growth of GaN were employed to generate the V-shaped microfacets along (1120) direction. The well-developed microfacets observed by scanning electron microscopy and the clear transmission electron microscope interfacial images indicated that the MQW was successfully grown on the GaN microfacets. Interestingly, cathodoluminescence (CL) spectra measured on the microfacets showed a continuous change in the luminescence peak positions. The CL peaks were shifted to a longer wavelength from 420 nm to 440 nm as the probing points were changed along upward direction. This could be attributed to the nonuniform distribution of the In composition and/or the wavefunction overlapping between adjacent wells. Present works thus propose a novel route to fabricate a monolithic white light emitting diode without phosphors by growing the InGaN/GaN MQWs on (1101) facet.

  14. Phonological Priming in Children's Picture Naming.

    ERIC Educational Resources Information Center

    Brooks, Patricia J.; MacWhinney, Brian

    2000-01-01

    Two experiments examined phonological priming in children and adults using a cross-modal picture-word interference task. Pictures of familiar objects were presented on a computer screen, while interfering words were presented over headphones. Results indicate that priming effects reach a peak during a time when articulatory information is being…

  15. Perceptual learning can reverse subliminal priming effects.

    PubMed

    Przekoracka-Krawczyk, Anna; Jaśkowski, Piotr

    2007-05-01

    Masked primes presented prior to a target can result in inverse priming (i.e., benefits on trials in which the prime and the target are mapped onto opposite responses). In five experiments, time-of-task effects on subliminal priming of motor responses were investigated. First, we replicated Klapp and Hinkley's (2002) finding that the priming effect is initially straight (i.e., it benefits congruent trials, in which the prime and targets are mapped onto the same response) or absent, and only later reverses (i.e., faster responses in incongruent than in congruent trials). We show that the presentation of the mask plays a crucial role in this reversal and that the reversal occurs later if the mask pattern is very complex. We suggest that perceptual learning improves the recognition of task-relevant features. Once recognized, these features can trigger the preparation of the alternative response and/or inhibit the prime-activated response. These findings support an active role of the mask in priming.

  16. Morphological Priming Survives a Language Switch

    ERIC Educational Resources Information Center

    Verdonschot, Rinus G.; Middelburg, Renee; Lensink, Saskia E.; Schiller, Niels O.

    2012-01-01

    In a long-lag morphological priming experiment, Dutch (L1)-English (L2) bilinguals were asked to name pictures and read aloud words. A design using non-switch blocks, consisting solely of Dutch stimuli, and switch-blocks, consisting of Dutch primes and targets with intervening English trials, was administered. Target picture naming was facilitated…

  17. Negative Priming in Free Recall Reconsidered

    ERIC Educational Resources Information Center

    Hanczakowski, Maciej; Beaman, C. Philip; Jones, Dylan M.

    2016-01-01

    Negative priming in free recall is the finding of impaired memory performance when previously ignored auditory distracters become targets of encoding and retrieval. This negative priming has been attributed to an aftereffect of deploying inhibitory mechanisms that serve to suppress auditory distraction and minimize interference with learning and…

  18. Visual Priming of Inverted and Rotated Objects

    ERIC Educational Resources Information Center

    Knowlton, Barbara J.; McAuliffe, Sean P.; Coelho, Chase J.; Hummel, John E.

    2009-01-01

    Object images are identified more efficiently after prior exposure. Here, the authors investigated shape representations supporting object priming. The dependent measure in all experiments was the minimum exposure duration required to correctly identify an object image in a rapid serial visual presentation stream. Priming was defined as the change…

  19. Can False Memories Prime Problem Solutions?

    ERIC Educational Resources Information Center

    Howe, Mark L.; Garner, Sarah R.; Dewhurst, Stephen A.; Ball, Linden J.

    2010-01-01

    Previous research has suggested that false memories can prime performance on related implicit and explicit memory tasks. The present research examined whether false memories can also be used to prime higher order cognitive processes, namely, insight-based problem solving. Participants were asked to solve a number of compound remote associate task…

  20. 7 CFR 29.2290 - Premature primings.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 2 2010-01-01 2010-01-01 false Premature primings. 29.2290 Section 29.2290 Agriculture Regulations of the Department of Agriculture AGRICULTURAL MARKETING SERVICE (Standards... 21) § 29.2290 Premature primings. Ground leaves harvested before reaching complete growth...

  1. Priming by the variability of visual information

    PubMed Central

    Michael, Elizabeth; de Gardelle, Vincent; Summerfield, Christopher

    2014-01-01

    According to recent theories, perception relies on summary representations that encode statistical information about the sensory environment. Here, we used perceptual priming to characterize the representations that mediate categorization of a complex visual array. Observers judged the average shape or color of a target visual array that was preceded by an irrelevant prime array. Manipulating the variability of task-relevant and task-irrelevant feature information in the prime and target orthogonally, we found that observers were faster to respond when the variability of feature information in the prime and target arrays matched. Critically, this effect occurred irrespective of whether the element-by-element features in the prime and target array overlapped or not, and was even present when prime and target features were drawn from opposing categories. This “priming by variance” phenomenon occurred with prime–target intervals as short as 100 ms. Further experiments showed that this effect did not depend on resource allocation, and occurred even when prime and target did not share the same spatial location. These results suggest that human observers adapt to the variability of visual information, and provide evidence for the existence of a low-level mechanism by which the range or dispersion of visual information is rapidly extracted. This information may in turn help to set the gain of neuronal processing during perceptual choice. PMID:24821803

  2. Priming Addition Facts with Semantic Relations

    ERIC Educational Resources Information Center

    Bassok, Miriam; Pedigo, Samuel F.; Oskarsson, An T.

    2008-01-01

    Results from 2 relational-priming experiments suggest the existence of an automatic analogical coordination between semantic and arithmetic relations. Word pairs denoting object sets served as primes in a task that elicits "obligatory" activation of addition facts (5 + 3 activates 8; J. LeFevre, J. Bisanz, & L. Mrkonjic, 1988). Semantic relations…

  3. The Actual Gemini 9 Prime Crew

    NASA Technical Reports Server (NTRS)

    1966-01-01

    The Gemini 9 backup crew members are, Commander, Thomas P. Stafford and pilot Eugene A. Cernan. The back-up crew became the prime crew when on February 28, 1966 the prime crew for the Gemini 9 mission were killed when their twin seat T- 38 trainer jet aircraft crashed into a building during a landing approach in bad weather.

  4. Does Verb Bias Modulate Syntactic Priming?

    ERIC Educational Resources Information Center

    Bernolet, Sarah; Hartsuiker, Robert J.

    2010-01-01

    In a corpus analysis of spontaneous speech Jaeger and Snider (2007) found that the strength of structural priming is correlated with verb alternation bias. This finding is consistent with an implicit learning account of syntactic priming: because the implicit learning model implemented by Chang (2002), Chang, Dell, and Bock (2006), and Chang,…

  5. Syntactic priming in American Sign Language.

    PubMed

    Hall, Matthew L; Ferreira, Victor S; Mayberry, Rachel I

    2015-01-01

    Psycholinguistic studies of sign language processing provide valuable opportunities to assess whether language phenomena, which are primarily studied in spoken language, are fundamentally shaped by peripheral biology. For example, we know that when given a choice between two syntactically permissible ways to express the same proposition, speakers tend to choose structures that were recently used, a phenomenon known as syntactic priming. Here, we report two experiments testing syntactic priming of a noun phrase construction in American Sign Language (ASL). Experiment 1 shows that second language (L2) signers with normal hearing exhibit syntactic priming in ASL and that priming is stronger when the head noun is repeated between prime and target (the lexical boost effect). Experiment 2 shows that syntactic priming is equally strong among deaf native L1 signers, deaf late L1 learners, and hearing L2 signers. Experiment 2 also tested for, but did not find evidence of, phonological or semantic boosts to syntactic priming in ASL. These results show that despite the profound differences between spoken and signed languages in terms of how they are produced and perceived, the psychological representation of sentence structure (as assessed by syntactic priming) operates similarly in sign and speech.

  6. Phasic Affective Modulation of Semantic Priming

    ERIC Educational Resources Information Center

    Topolinski, Sascha; Deutsch, Roland

    2013-01-01

    The present research demonstrates that very brief variations in affect, being around 1 s in length and changing from trial to trial independently from semantic relatedness of primes and targets, modulate the amount of semantic priming. Implementing consonant and dissonant chords (Experiments 1 and 5), naturalistic sounds (Experiment 2), and visual…

  7. Does translation involve structural priming?

    PubMed

    Maier, Robert M; Pickering, Martin J; Hartsuiker, Robert J

    2017-08-01

    When asked to translate utterances, people might merely make sure that their translations have the same meaning as the source, but they might also maintain aspects of sentence form across languages. We report two experiments in which English-German and German-English bilinguals (without specialist translator training) repeated German ditransitive sentences whose meaning was compatible with more than one grammatical form or translated them into English. Participants almost invariably repeated the sentences accurately, thereby retaining the grammatical structure. Importantly, Experiment 1 found that they tended to repeat grammatical form across languages. Experiment 2 included a condition with sentences that had no grammatical equivalent form in English; here participants tended to persist in the order of thematic roles. We argue that cross-linguistic structural priming plays a major role in the act of translation.

  8. The Apollo 11 Prime Crew

    NASA Technical Reports Server (NTRS)

    1969-01-01

    Portrait of the prime crew of the Apollo 11 lunar landing mission. From left to right they are: Commander, Neil A. Armstrong, Command Module Pilot, Michael Collins, and Lunar Module Pilot, Edwin E. Aldrin Jr. On July 20th 1969 at 4:18 PM, EDT the Lunar Module 'Eagle' landed in a region of the Moon called the Mare Tranquillitatis, also known as the Sea of Tranquillity. After securing his spacecraft, Armstrong radioed back to earth: 'Houston, Tranquility Base here, the Eagle has landed'. At 10:56 p.m. that same evening and witnessed by a worldwide television audience, Neil Armstrong stepped off the 'Eagle's landing pad onto the lunar surface and said: 'That's one small step for a man, one giant leap for mankind.' He became the first human to set foot upon the Moon.

  9. Nanoheteroepitaxy of GaN on AlN/Si(111) nanorods fabricated by nanosphere lithography

    NASA Astrophysics Data System (ADS)

    Lee, Donghyun; Shin, In-Su; Jin, Lu; Kim, Donghyun; Park, Yongjo; Yoon, Euijoon

    2016-06-01

    Nanoheteroepitaxy (NHE) of GaN on an AlN/Si(111) nanorod structure was investigated by metal-organic chemical vapor deposition. Silica nanosphere lithography was employed to fabricate a periodic hexagonal nanorod array with a narrow gap of 30 nm between the nanorods. We were successful in obtaining a fully coalesced GaN film on the AlN/Si(111) nanorod structure. Transmission electron microscopy revealed that threading dislocation (TD) bending and termination by stacking faults occurred near the interface between GaN and the AlN/Si(111) nanorods, resulting in the reduction of TD density for the NHE GaN layer. The full width at half-maximum of the X-ray rocking curve for (102) plane of the NHE GaN was found to decrease down to 728 arcsec from 1005 arcsec for the GaN layer on a planar AlN/Si(111) substrate, indicating that the crystalline quality of the NHE GaN was improved. Also, micro-Raman measurement showed that tensile stress in the NHE GaN layer was reduced significantly as much as 70% by introducing air voids between the nanorods.

  10. Opportunities and challenges in GaN metal organic chemical vapor deposition for electron devices

    NASA Astrophysics Data System (ADS)

    Matsumoto, Koh; Yamaoka, Yuya; Ubukata, Akinori; Arimura, Tadanobu; Piao, Guanxi; Yano, Yoshiki; Tokunaga, Hiroki; Tabuchi, Toshiya

    2016-05-01

    The current situation and next challenge in GaN metal organic chemical vapor deposition (MOCVD) for electron devices of both GaN on Si and GaN on GaN are presented. We have examined the possibility of increasing the growth rate of GaN on 200-mm-diameter Si by using a multiwafer production MOCVD machine, in which the vapor phase parasitic reaction is well controlled. The impact of a high-growth-rate strained-layer-superlattice (SLS) buffer layer is presented in terms of material properties. An SLS growth rate of as high as 3.46 µm/h, which was 73% higher than the current optimum, was demonstrated. As a result, comparable material properties were obtained. Next, a typical result of GaN doped with Si of 1 × 1016 cm-3 grown at the growth rate of 3.7 µm/h is shown. For high-voltage application, we need a thick high-purity GaN drift layer with a low carbon concentration, of less than 1016 cm-3. It is shown that achieving a high growth rate by precise control of the vapor phase reaction is still challenge in GaN MOCVD.

  11. Terahertz study of m-plane GaN thin fims

    NASA Astrophysics Data System (ADS)

    Quadir, Shaham; Jang, Der-Jun; Lin, Ching-Liang; Lo, Ikai

    2014-03-01

    We investigate the optical properties of m-plane GaN thin films using the terahertz time domain spectroscopy. The m-plane GaN thin films were grown on γ-LiAlO2 substrates with buffer layers of low temperature grown GaN. The thin films were illuminated with terahertz radiation generated by a LT-GaAs antenna and the transmitted signal was detected by a ZnTe crystal. The polarization of the terahertz wave was chosen to be either parallel or perpendicular to the GaN [0001] direction. We compared the transmitted signals of the m-plane GaN thin films to that of the LAO substrate. The samples as well as the LAO substrate exhibited polarization dependence of absorption in terahertz spectrum. The carrier densities and the mobilities were derived from the transmittance of the THz wave using extended Drude model. We found, in all samples, both the carrier densities and mobilities along the GaN [0001] direction were smaller than those along the GaN [1120] direction due to the stripe formation along the GaN [1120].

  12. Viability and proliferation of endothelial cells upon exposure to GaN nanoparticles

    PubMed Central

    Braniste, Tudor; Tiginyanu, Ion; Horvath, Tibor; Raevschi, Simion; Cebotari, Serghei; Lux, Marco; Haverich, Axel

    2016-01-01

    Summary Nanotechnology is a rapidly growing and promising field of interest in medicine; however, nanoparticle–cell interactions are not yet fully understood. The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN) semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. To functionalize surfaces with GaN, GaN nanoparticles were synthesized on a sacrificial layer of zinc oxide (ZnO) nanoparticles using hydride vapor phase epitaxy. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN. PMID:27826507

  13. Object color affects identification and repetition priming.

    PubMed

    Uttl, Bob; Graf, Peter; Santacruz, Pilar

    2006-10-01

    We investigated the influence of color on the identification of both non-studied and studied objects. Participants studied black and white and color photos of common objects and memory was assessed with an identification test. Consistent with our meta-analysis of prior research, we found that objects were easier to identify from color than from black and white photos. We also found substantial priming in all conditions, and study-to-test changes in an object's color reduced the magnitude of priming. Color-specific priming effects were large for color-complex objects, but minimal for color-simple objects. The pattern and magnitude of priming effects was not influenced either by the extent to which an object always appears in the same color (i.e., whether a color is symptomatic of an object) or by the object's origin (natural versus fabricated). We discuss the implications of our findings for theoretical accounts of object perception and repetition priming.

  14. Priming analogical reasoning with false memories.

    PubMed

    Howe, Mark L; Garner, Sarah R; Threadgold, Emma; Ball, Linden J

    2015-08-01

    Like true memories, false memories are capable of priming answers to insight-based problems. Recent research has attempted to extend this paradigm to more advanced problem-solving tasks, including those involving verbal analogical reasoning. However, these experiments are constrained inasmuch as problem solutions could be generated via spreading activation mechanisms (much like false memories themselves) rather than using complex reasoning processes. In three experiments we examined false memory priming of complex analogical reasoning tasks in the absence of simple semantic associations. In Experiment 1, we demonstrated the robustness of false memory priming in analogical reasoning when backward associative strength among the problem terms was eliminated. In Experiments 2a and 2b, we extended these findings by demonstrating priming on newly created homonym analogies that can only be solved by inhibiting semantic associations within the analogy. Overall, the findings of the present experiments provide evidence that the efficacy of false memory priming extends to complex analogical reasoning problems.

  15. Individual Differences in Working Memory Capacity Modulates Semantic Negative Priming from Single Prime Words

    PubMed Central

    Ortells, Juan J.; Noguera, Carmen; Álvarez, Dolores; Carmona, Encarna; Houghton, George

    2016-01-01

    The present study investigated whether semantic negative priming from single prime words depends on the availability of cognitive control resources. Participants with high vs. low working memory capacity (as assessed by their performance in complex span and attentional control tasks) were instructed to either attend to or ignore a briefly presented single prime word that was followed by either a semantically related or unrelated target word on which participants made a lexical decision. Individual differences in working memory capacity (WMC) mainly affected the processing of the ignored primes, but not the processing of the attended primes: While the latter produced reliable positive semantic priming for both high- and low-WMC participants, the former gave rise to reliable semantic negative priming only for high WMC participants, with low WMC participants showing the opposite positive priming effect. The present results extend previous findings in demonstrating that (a) single negative priming can reliably generalize to semantic associates of the prime words, and (b) a differential availability of cognitive control resources can reliably modulate the negative priming effect at a semantic level of representation. PMID:27621716

  16. Shifting Evaluation Windows: Predictable Forward Primes with Long SOAs Eliminate the Impact of Backward Primes

    PubMed Central

    Fockenberg, Daniel A.; Koole, Sander L.; Lakens, Daniël; Semin, Gün R.

    2013-01-01

    Recent work suggests that people evaluate target stimuli within short and flexible time periods called evaluation windows. Stimuli that briefly precede a target (forward primes) or briefly succeed a target (backward primes) are often included in the target's evaluation. In this article, the authors propose that predictable forward primes act as “go” signals that prepare target processing, such that earlier forward primes pull the evaluation windows forward in time. Earlier forward primes may thus reduce the impact of backward primes. This shifting evaluation windows hypothesis was tested in two experiments using an evaluative decision task with predictable (vs. unpredictable) forward and backward primes. As expected, a longer time interval between a predictable forward prime and a target eliminated backward priming. In contrast, the time interval between an unpredictable forward primes and a target had no effects on backward priming. These findings suggest that predictable features of dynamic stimuli can shape target extraction by determining which information is included (or excluded) in rapid evaluation processes. PMID:23359809

  17. The effect of prime duration in masked orthographic priming depends on neighborhood distribution.

    PubMed

    Robert, Christelle; Mathey, Stéphanie

    2012-06-01

    A lexical decision task was used with a masked priming procedure to investigate whether and to what extent neighborhood distribution influences the effect of prime duration in masked orthographic priming. French word targets had two higher frequency neighbors that were either distributed over two letter positions (e.g., LOBE/robe-loge) or concentrated on a single letter position (e.g., FARD/tard-lard). Word targets were preceded by their highest frequency neighbor or by a control prime. Four prime durations were compared (27, 39, 53, and 67 ms). Results showed that the inhibitory priming effect found for words with distributed neighbors at a 67-ms stimulus onset asynchrony (SOA) was canceled when prime duration decreased. In contrast, no priming effect was found in any of the four prime durations for words with concentrated neighbors. Simulations run on the word materials revealed that the interactive activation model (McClelland & Rumelhart, 1981) captured the increasing inhibitory priming effect in the distributed neighbor condition but failed to capture the loss of priming in the concentrated neighbor condition.

  18. Correlation between prime duration and semantic priming effect: evidence from N400 effect.

    PubMed

    Liu, B; Wu, G; Meng, X; Dang, J

    2013-05-15

    When the prime word is masked and flashed very quickly, its presence cannot be perceived by the subjects, but it can still accelerate the processing of the subsequent relevant target stimulus. This is known as the masked priming effect. Adopting a similar experimental paradigm, in this study we take the gray scale pictures describing ordinary objects as prime stimuli and the environmental sounds as target stimuli. The subjects are then asked to classify the target sounds to investigate whether incongruent target sounds elicit the N400 semantic priming effect. At the same time, the prime-mask withdraw value is made at these time intervals: 16ms, 33ms, 50ms, 66ms and 83ms, so as to reveal whether there exists a correlation between the prime duration and the priming effect. The result shows that, at each time interval, the processing of sounds that are congruent with prime pictures is sped up and sounds that are incongruent with prime pictures trigger the N400 effect. The amplitude of the N400 effect is enlarged proportionally with the time interval and gradually approaches the point of saturation. Given this, it is believed that the N400 effect reflects automatic semantic processing, that consciousness is not a prerequisite of semantic priming, and that early visual information has an accumulative priming effect on target sounds.

  19. Individual Differences in Working Memory Capacity Modulates Semantic Negative Priming from Single Prime Words.

    PubMed

    Ortells, Juan J; Noguera, Carmen; Álvarez, Dolores; Carmona, Encarna; Houghton, George

    2016-01-01

    The present study investigated whether semantic negative priming from single prime words depends on the availability of cognitive control resources. Participants with high vs. low working memory capacity (as assessed by their performance in complex span and attentional control tasks) were instructed to either attend to or ignore a briefly presented single prime word that was followed by either a semantically related or unrelated target word on which participants made a lexical decision. Individual differences in working memory capacity (WMC) mainly affected the processing of the ignored primes, but not the processing of the attended primes: While the latter produced reliable positive semantic priming for both high- and low-WMC participants, the former gave rise to reliable semantic negative priming only for high WMC participants, with low WMC participants showing the opposite positive priming effect. The present results extend previous findings in demonstrating that (a) single negative priming can reliably generalize to semantic associates of the prime words, and (b) a differential availability of cognitive control resources can reliably modulate the negative priming effect at a semantic level of representation.

  20. Movement-Based Priming: Clinical Applications and Neural Mechanisms.

    PubMed

    Stoykov, Mary Ellen; Corcos, Daniel Montie; Madhavan, Sangeetha

    2017-01-01

    Priming can be described as behavior change generated by preceding stimuli. Although various types of priming have been long studied in the field of psychology, priming that targets motor cortex is a relatively new topic of research in the fields of motor control and rehabilitation. In reference to a rehabilitation intervention, priming is categorized as a restorative approach. There are a myriad of possible priming approaches including noninvasive brain stimulation, motor imagery, and sensory-based priming, to name a few. The authors report on movement-based priming which, compared to other priming types, is less frequently examined and under reported. Movement-based priming includes, but is not limited to, bilateral motor priming, unilateral priming, and aerobic exercise. Clinical and neural mechanistic aspects of movement-based priming techniques are explored.

  1. Masked priming by misspellings: Word frequency moderates the effects of SOA and prime-target similarity.

    PubMed

    Burt, Jennifer S

    2016-02-01

    University students made lexical decisions to eight- or nine-letter words preceded by masked primes that were the target, an unrelated word, or a typical misspelling of the target. At a stimulus onset asynchrony (SOA) of 47 ms, primes that were misspellings of the target produced a priming benefit for low-, medium-, and high-frequency words, even when the misspelled primes were changed to differ phonologically from their targets. At a longer SOA of 80 ms, misspelled primes facilitated lexical decisions only to medium- and low-frequency targets, and a phonological change attenuated the benefit for medium-frequency targets. The results indicate that orthographic similarity can be preserved over changes in letter position and word length, and that the priming effect of misspelled words at the shorter SOA is orthographically based. Orthographic-priming effects depend on the quality of the orthographic learning of the target word.

  2. Reading a standing wave: figure-ground-alternation masking of primes in evaluative priming.

    PubMed

    Bermeitinger, Christina; Kuhlmann, Michael; Wentura, Dirk

    2012-09-01

    We propose a new masking technique for masking word stimuli. Drawing on the phenomena of metacontrast and paracontrast, we alternately presented two prime displays of the same word with the background color in one display matching the font color in the other display and vice versa. The sequence of twenty alterations (spanning approx. 267 ms) was sandwich-masked by structure masks. Using this masking technique, we conducted evaluative priming experiments with positive and negative target and prime words. Significant priming effects were found - for primes and targets drawn from the same as well as from different word sets. Priming effects were independent of prime discrimination performance in direct tests and they were still significant after the sample was restricted to those participants who showed random responding in the direct test.

  3. Semipolar single component GaN on planar high index Si(11h) substrates

    SciTech Connect

    Ravash, Roghaiyeh; Blaesing, Juergen; Dadgar, Armin; Krost, Alois

    2010-10-04

    We present metal organic vapor phase epitaxy growth of polarization reduced, single component GaN on nonpatterned Si(112), Si(113), Si(114), Si(115), and Si(116) substrates. We find that the inclination angle of GaN c-axis with respect to the surface normal depends on the angle between Si(111) and above mentioned Si(11h)-surfaces. The growth of the GaN layer is essentially performed as c-axis oriented growth on the naturally occurring Si(111) facets of these Si(11h)-surfaces. The c-axis tilt-angle of GaN crystallites depends on the Si-surface direction and increases from Si(112) to Si(116) planes. GaN layers are investigated by x-ray analysis and scanning electron microscopy.

  4. Hole-induced d0 ferromagnetism enhanced by Na-doping in GaN

    NASA Astrophysics Data System (ADS)

    Zhang, Yong; Li, Feng

    2017-02-01

    The d0 ferromagnetism in wurtzite GaN is investigated by the first-principle calculations. It is found that spontaneous magnetization occurs if sufficient holes are injected in GaN. Both Ga vacancy and Na doping can introduce holes into GaN. However, Ga vacancy has a high formation energy, and is thus unlikely to occur in a significant concentration. In contrast, Na doping has relatively low formation energy. Under N-rich growth condition, Na doping with a sufficient concentration can be achieved, which can induce half-metallic ferromagnetism in GaN. Moreover, the estimated Curie temperature of Na-doped GaN is well above the room temperature.

  5. Step-induced misorientation of GaN grown on r-plane sapphire

    SciTech Connect

    Smalc-Koziorowska, J.; Dimitrakopulos, G. P.; Sahonta, S.-L.; Komninou, Ph.; Tsiakatouras, G.; Georgakilas, A.

    2008-07-14

    In the growth of nonpolar (1120) a-plane GaN on r-plane (1102) sapphire by plasma-assisted molecular beam epitaxy, misoriented crystallites are observed close to the substrate. They have average diameter {approx}10 nm and are oriented with the (0001){sub GaN} plane approximately parallel to the (2113){sub sapph.} plane and [0110]{sub GaN} parallel [1101]{sub sapph.}. This semipolar orientation is promoted by a low misfit (2.4%) between (1011){sub GaN} and (1210){sub sapph.} planes. Its introduction, after nitridation treatment, is due to GaN nucleation on (2113){sub sapph.} step facets inclined at 26 deg. relative to the r-plane. Two variants are observed, leading to twinning when they abut inside the epilayer.

  6. Vertical nonpolar growth templates for light emitting diodes formed with GaN nanosheets

    NASA Astrophysics Data System (ADS)

    Yeh, Ting-Wei; Lin, Yen-Ting; Ahn, Byungmin; Stewart, Lawrence S.; Daniel Dapkus, P.; Nutt, Steven R.

    2012-01-01

    We demonstrate that nonpolar m-plane surfaces can be generated on uniform GaN nanosheet arrays grown vertically from the (0001)-GaN bulk material. InGaN/GaN multiple quantum wells (MQWs) grown on the facets of these nanosheets are demonstrated by cross-sectional transmission electron microscopy. Owing to the high aspect ratio of the GaN nanosheet structure, the MQWs predominantly grow on nonpolar GaN planes. The results suggest that GaN nanosheets provide a conduction path for device fabrication and also a growth template to reduce the piezoelectric field inside the active region of InGaN-based light emitting diodes.

  7. Prospects for the application of GaN power devices in hybrid electric vehicle drive systems

    NASA Astrophysics Data System (ADS)

    Su, Ming; Chen, Chingchi; Rajan, Siddharth

    2013-07-01

    GaN, a wide bandgap semiconductor successfully implemented in optical and high-speed electronic devices, has gained momentum in recent years for power electronics applications. Along with rapid progress in material and device processing technologies, high-voltage transistors over 600 V have been reported by a number of teams worldwide. These advances make GaN highly attractive for the growing market of electrified vehicles, which currently employ bipolar silicon devices in the 600-1200 V class for the traction inverter. However, to capture this billion-dollar power market, GaN has to compete with existing IGBT products and deliver higher performance at comparable or lower cost. This paper reviews key achievements made by the GaN semiconductor industry, requirements of the automotive electric drive system and remaining challenges for GaN power devices to fit in the inverter application of hybrid vehicles.

  8. Hydrogen sensing characteristics of semipolar (112{sup ¯}2) GaN Schottky diodes

    SciTech Connect

    Hyeon Baik, Kwang; Kim, Hyonwoong; Jang, Soohwan; Lee, Sung-Nam; Lim, Eunju; Pearton, S. J.; Ren, F.

    2014-02-17

    The hydrogen detection characteristics of semipolar (112{sup ¯}2) plane GaN Schottky diodes were investigated and compared to c-plane Ga- and N-polar and nonpolar a-plane (112{sup ¯}0) GaN diodes. The semipolar GaN diodes showed large current response to 4% hydrogen in nitrogen gas with an accompanying Schottky barrier reduction of 0.53 eV at 25 °C, and the devices exhibited full recovery to the initial current level upon switching to a nitrogen ambient. The current-voltage characteristics of the semipolar devices remained rectifying after hydrogen exposure, in sharp contrast to the case of c-plane N-polar GaN. These results show that the surface atom configuration and polarity play a strong role in hydrogen sensing with GaN.

  9. Improvement of Crystalline Quality in GaN Films by Air-Bridged Lateral Epitaxial Growth

    NASA Astrophysics Data System (ADS)

    Kidoguchi, Isao; Ishibashi, Akihiko; Sugahara, Gaku; Tsujimura, Ayumu; Ban, Yuzaburoh

    2000-05-01

    Air-bridged lateral epitaxial growth (ABLEG), a new technique of lateral growth of GaN films, has been developed using low-pressure metalorganic vapor phase epitaxy. A previously grown 1-μm-thick GaN film is grooved along the < 1{\\bar 1}00 >\\textrm{GaN} direction, and the bottoms of the trenches and the sidewalls are covered with a silicon nitride mask. A free-standing GaN material is regrown from the exposed (0001) surface of the ridged GaN seed structure. Cross-sectional transmission electron microscopy analysis reveals that the dislocations originating from the underlying seed GaN extend straight in the < 0001 > direction and dislocations do not propagate into the wing region. The wing region also exhibits a smooth surface and the root mean square roughness is found to be 0.088 nm by atomic force microscopy measurement of the (0001) face of the wing region.

  10. Influence of Ga/N ratio on morphology, vacancies, and electrical transport in GaN grown by molecular beam epitaxy at high temperature

    NASA Astrophysics Data System (ADS)

    Koblmüller, G.; Reurings, F.; Tuomisto, F.; Speck, J. S.

    2010-11-01

    The effect of Ga/N flux ratio on surface morphology, incorporation of point defects and electrical transport properties of GaN films grown by plasma-assisted molecular beam epitaxy in a recently developed high-temperature growth regime was investigated. The homoepitaxial (0001) GaN films grown at ˜780-790 °C showed smoothest morphologies near the cross-over between N-rich and Ga-rich growth (0.75<Ga/N<1.1) contrasting previous observations for low-temperature growth. The higher-quality growth near Ga/N˜1 resulted from lower thermal decomposition rates and was corroborated by slightly lower Ga vacancy concentrations [VGa], lower unintentional oxygen incorporation, and improved electron mobilities. The consistently low [VGa], i.e., ˜1016 cm-3 for all films attribute further to the significant benefits of the high-temperature growth regime.

  11. Optical and structural properties of GaN nanopillar and nanostripe arrays with embedded InGaN /GaN multi-quantum wells

    NASA Astrophysics Data System (ADS)

    Keller, S.; Schaake, C.; Fichtenbaum, N. A.; Neufeld, C. J.; Wu, Y.; McGroddy, K.; David, A.; DenBaars, S. P.; Weisbuch, C.; Speck, J. S.; Mishra, U. K.

    2006-09-01

    GaN nanopillar and nanostripe arrays with embedded InGaN /GaN multi-quantum wells (MQWs) were fabricated by holographic lithography and subsequent reactive ion etching. Etch related damage of the nanostructures was successfully healed through annealing in NH3/N2 mixtures under optimized conditions. The nanopatterned samples exhibited enhanced luminescence in comparison to the planar wafers. X-ray reciprocal space maps recorded around the asymmetric (101¯5) reflection revealed that the MQWs in both nanopillars and nanostripes relaxed after nanopatterning and adopted a larger in-plane lattice constant than the underlying GaN layer. The pillar relaxation process had no measurable effect on the Stokes shift typically observed in MQWs on c-plane GaN, as evaluated by excitation power dependent photoluminescence (PL) measurements. Angular-resolved PL measurements revealed the extraction of guided modes from the nanopillar arrays.

  12. Polarity of semipolar wurtzite crystals: X-ray photoelectron diffraction from GaN(101⁻1) and GaN(202⁻1) surfaces

    SciTech Connect

    Romanyuk, O. Jiříček, P.; Bartoš, I.; Paskova, T.

    2014-09-14

    Polarity of semipolar GaN(101⁻1) (101⁻1⁻) and GaN(202⁻1) (202⁻1⁻) surfaces was determined with X-ray photoelectron diffraction (XPD) using a standard MgKα source. The photoelectron emission from N 1s core level measured in the a-plane of the crystals shows significant differences for the two crystal orientations within the polar angle range of 80–100° from the (0001) normal. It was demonstrated that XPD polar plots recorded in the a-plane are similar for each polarity of the GaN(101⁻1) and GaN(202⁻1) crystals if referred to (0001) crystal axes. For polarity determinations of all important GaN(h0h⁻l) semipolar surfaces, the above given polar angle range is suitable.

  13. 1.2 kV GaN Schottky barrier diodes on free-standing GaN wafer using a CMOS-compatible contact material

    NASA Astrophysics Data System (ADS)

    Liu, Xinke; Liu, Qiang; Li, Chao; Wang, Jianfeng; Yu, Wenjie; Xu, Ke; Ao, Jin-Ping

    2017-02-01

    In this paper, we report the formation of vertical GaN Schottky barrier diodes (SBDs) on a 2-in. free-standing (FS) GaN wafer, using CMOS-compatible contact material. By realizing an off-state breakdown voltage V BR of 1200 V and an on-state resistance R on of 7 mΩ·cm2, the FS-GaN SBDs fabricated in this work achieve a power device figure-of-merit V\\text{BR}2/R\\text{on} of 2.1 × 108 V2·Ω-1·cm-2 on a high quality GaN wafer. In addition, the fabricated FS-GaN SBDs show the highest I on/I off current ratio of ˜2.3 × 1010 among the GaN SBDs reported in the literature.

  14. Influence of GaN column diameter on structural properties for InGaN nanocolumns grown on top of GaN nanocolumns

    NASA Astrophysics Data System (ADS)

    Oto, Takao; Mizuno, Yutaro; Yanagihara, Ai; Miyagawa, Rin; Kano, Tatsuya; Yoshida, Jun; Sakakibara, Naoki; Kishino, Katsumi

    2016-11-01

    The influence of GaN column diameter DGaN on structural properties was systematically investigated for InGaN nanocolumns (NCs) grown on top of GaN NCs. We demonstrated a large critical layer thickness of above 400 nm for In0.3Ga0.7N/GaN NCs. The structural properties were changed at the boundary of DGaN=D0 (˜120 nm). Homogeneous InGaN NCs grew axially on the GaN NCs with DGaN≤D0, while InGaN-InGaN core-shell structures were spontaneously formed on the GaN NCs with DGaN>D0. These results can be explained by a growth system that minimizes the total strain energy of the NCs.

  15. Improved emission efficiency of a-plane GaN light emitting diodes with silica nano-spheres integrated into a-plane GaN buffer layer

    NASA Astrophysics Data System (ADS)

    Park, S. H.; Park, J.; You, D.-J.; Joo, K.; Moon, D.; Jang, J.; Kim, D.-U.; Chang, H.; Moon, S.; Song, Y.-K.; Lee, G.-D.; Jeon, H.; Xu, J.; Nanishi, Y.; Yoon, E.

    2012-05-01

    A simple and inexpensive technique to improve the emission efficiency of nonpolar a-plane light emitting diodes (LEDs) is proposed. The 3-dimensional growth nature of a-plane GaN was utilized to form the regrowth template of a-plane GaN. Subsequently, the controlled integration of silica nano-spheres (CIS) into the regrowth template is performed to improve the crystal quality of a-plane GaN by epitaxial lateral overgrowth method. In addition, the CIS improves light extraction by the scattering process. The light output power from the CIS a-plane GaN LEDs showed 130%-150% increase compared to that of LED without silica nano-spheres.

  16. Rokumi-jio-gan-Containing Prescriptions Attenuate Oxidative Stress, Inflammation, and Apoptosis in the Remnant Kidney

    PubMed Central

    Park, Chan Hum; Lee, Sul Lim; Okamoto, Takuya; Tanaka, Takashi; Yokozawa, Takako

    2012-01-01

    Two Rokumi-jio-gan-containing prescriptions (Hachimi-jio-gan and Bakumi-jio-gan) were selected to examine their actions in nephrectomized rats. Each prescription was given orally to rats for 10 weeks after the excision of five-sixths of their kidney volumes, and its effect was compared with non-nephrectomized and normal rats. Rats given Hachimi-jio-gan and Bakumi-jio-gan showed an improvement of renal functional parameters such as serum urea nitrogen, creatinine, creatinine clearance, and urinary protein. The nephrectomized rats exhibited the up-regulation of nicotinamide adenine dinucleotide phosphate oxidase subunits, c-Jun N-terminal kinase (JNK), phosphor-JNK, c-Jun, transforming growth factor-β1, nuclear factor-kappa B, cyclooxygenase-2, inducible nitric oxide synthase, monocyte chemotactic protein-1, intracellular adhesion molecule-1, Bax, cytochrome c, and caspase-3, and down-regulation of NF-E2-related factor 2, heme oxygenase-1, and survivin; however, Bakumi-jio-gan administration acts as a regulator in inflammatory reactions caused by oxidative stress in renal failure. Moreover, the JNK pathway and apoptosis-related protein expressions, Bax, caspase-3, and survivin, were ameliorated to the normal levels by Hachimi-jio-gan administration. The development of renal lesions, glomerular sclerosis, tubulointerstitial damage, and arteriolar sclerotic lesions, estimated by histopathological evaluation and scoring, was strong in the groups administered Hachimi-jio-gan rather than Bakumi-jio-gan. This study suggests that Rokumi-jio-gan-containing prescriptions play a protective role in the progression of renal failure. PMID:23243456

  17. Enhancement in wafer bow of free-standing GaN substrates due to high-dose hydrogen implantation: implications for GaN layer transfer applications

    NASA Astrophysics Data System (ADS)

    Singh, R.; Radu, I.; Bruederl, G.; Eichler, C.; Haerle, V.; Gösele, U.; Christiansen, S. H.

    2007-04-01

    Two-inch free-standing GaN wafers were implanted by 100 keV H+2 ions with a dose of 1.3 × 1017 cm-2 at room temperature. The hydrogen implantation induced damage in GaN extends between 230 to 500 nm from the surface as measured by cross-sectional transmission electron microscopy (XTEM). The wafer bow of the free-standing GaN wafers was measured using a Tencor long range profilometer on a scan length of 48 mm before and after the hydrogen implantation. Before implantation the bow of two different free-standing GaN wafers (named A and B) with different thicknesses was 1.5 µm and 6 µm, respectively. Initially, both wafers were concave in shape. After implantation the bow changed to convex with a value of 36 µm for wafer A and a value of 32 µm for wafer B. High dose hydrogen implantation leads to an in-plane compressive stress in the top damaged layer of the GaN, which is responsible for the enhancement of wafer bow and change of bow direction. The high value of bow after implantation hinders the direct wafer bonding of the free-standing GaN wafers to sapphire or any other handle wafers. Tight bonding between hydrogen implanted GaN wafers and the handle wafers is a necessary requirement for the successful layer transfer of thin GaN layers onto other substrates based on wafer bonding and layer splitting (Smart-cut).

  18. Phonological and Orthographic Overlap Effects in Fast and Masked Priming

    PubMed Central

    Frisson, Steven; Bélanger, Nathalie N.; Rayner, Keith

    2014-01-01

    We investigated how orthographic and phonological information is activated during reading, using a fast priming task, and during single word recognition, using masked priming. Specifically, different types of overlap between prime and target were contrasted: high orthographic and high phonological overlap (track-crack), high orthographic and low phonological overlap (bear-gear), or low orthographic and high phonological overlap (fruit-chute). In addition, we examined whether (orthographic) beginning overlap (swoop-swoon) yielded the same priming pattern as end (rhyme) overlap (track-crack). Prime durations were 32 and 50ms in the fast priming version, and 50ms in the masked priming version, and mode of presentation (prime and target in lower case) was identical. The fast priming experiment showed facilitatory priming effects when both orthography and phonology overlapped, with no apparent differences between beginning and end overlap pairs. Facilitation was also found when prime and target only overlapped orthographically. In contrast, the masked priming experiment showed inhibition for both types of end overlap pairs (with and without phonological overlap), and no difference for begin overlap items. When prime and target only shared principally phonological information, facilitation was only found with a long prime duration in the fast priming experiment, while no differences were found in the masked priming version. These contrasting results suggest that fast priming and masked priming do not necessarily tap into the same type of processing. PMID:24365065

  19. Fabrication of GaN Microporous Structure at a GaN/Sapphire Interface as the Template for Thick-Film GaN Separation Grown by HVPE

    NASA Astrophysics Data System (ADS)

    Chen, Jianli; Cheng, Hongjuan; Zhang, Song; Lan, Feifei; Qi, Chengjun; Xu, Yongkuan; Wang, Zaien; Li, Jing; Lai, Zhanping

    2016-10-01

    In this paper, a microporous structure at the GaN/sapphire interface has been obtained by an electrochemical etching method via a selective etching progress using an as-grown GaN/sapphire wafer grown by metal organic chemical vapor deposition. The as-prepared GaN interfacial microporous structure has been used as a template for the following growth of thick-film GaN crystal by hydride vapor phase epitaxy (HVPE), facilitating the fabrication of a free-standing GaN substrate detached from a sapphire substrate. The evolution of the interfacial microporous structure has been investigated by varying the etching voltages and time, and the formation mechanism of interfacial microporous structure has been discussed in detail as well. Appropriate interfacial microporous structure is beneficial for separating the thick GaN crystal grown by HVPE from sapphire during the cooling down process. The separation that occurred at the place of interfacial microporous can be attributed to the large thermal strain between GaN and sapphire. This work realized the fabrication of a free-standing GaN substrate with high crystal quality and nearly no residual strain.

  20. Re-naming D Double Prime

    NASA Technical Reports Server (NTRS)

    Chao, Benjamin F.

    1999-01-01

    "Knowledge about the dynamics of the D double prime region is a key to unlock some fundamental mysteries of the Earth heat engine which governs a wide range of global geophysical processes from tectonics to geodynamo." This benign sentence makes complete sense to many geophysicists. But for many others, it makes sense all except the odd nomenclature "D double prime". One knows about the crust, upper and lower mantle, outer and inner core, but where is the D double prime region? What meaning does it try to convey? Where is D prime region, or D, or A, B, C regions for that matter, and are there higher-order primes? How does such an odd name come about anyway? D double prime, or more "simply" D", is a generic designation given to the thin shell, about 200 km thick, of the lowermost mantle just above the core-mantle boundary inside the Earth. Incidentally, whether D" is "simpler" than "D double prime" depends on whether you are pronouncing it or writing/typing it; and D" can be confusing to readers in distinguishing quotation marks (such as in the above sentences) and second derivatives, and to word processors in spelling check and indexing.

  1. Electrophysiology reveals semantic priming at a short SOA irrespective of depth of prime processing.

    PubMed

    Küper, Kristina; Heil, Martin

    2009-04-03

    The otherwise robust behavioral semantic priming effect is reduced to the point of being absent when a letter search has to be performed on the prime word. As a result the automaticity of semantic activation has been called into question. It is unclear, however, in how far automatic processes are even measurable in the letter search priming paradigm as the prime task necessitates a long prime-probe stimulus-onset asynchrony (SOA). In a modified procedure, a short SOA can be realized by delaying the prime task response until after participants have made a lexical decision on the probe. While the absence of lexical decision priming has already been demonstrated in this design it seems premature to draw any definite conclusions from this purely behavioral result since event related potential (ERP) measures have been shown to be a more sensitive index of semantic activation. Using the modified paradigm we thus recorded ERP in addition to lexical decision times. Stimuli were presented at two different SOAs (240 ms vs. 840 ms) and participants performed either a grammatical discrimination (Experiment 1) or a letter search (Experiment 2) on the prime. Irrespective of prime task, the modulation of the N400, the ERP correlate of semantic activation, provided clear-cut evidence of semantic processing at the short SOA. Implications for theories of semantic activation as well as the constraints of the delayed prime task procedure are discussed.

  2. Optical properties of GaN wurtzite quantum wires

    NASA Astrophysics Data System (ADS)

    Zhang, X. W.; Xia, J. B.

    2006-03-01

    The electronic structure and optical properties of freestanding GaN wurtzite quantum wires are studied in the framework of six-band effective-mass envelope function theory. It is found that the electron states are either twofold or fourfold degenerate. There is a dark exciton effect when the radius R of GaN wurtzite quantum wires is in the range of [0.7, 10.9] nm. The linear polarization factors are calculated in three cases, the quantum confinement effect (finite long wire), the dielectric effect and both effects (infinitely long wire). It is found that the linear polarization factor of a finite long wire whose length is much less than the electromagnetic wavelength decreases as R increases, is very close to unity (0.979) at R = 1 nm, and changes from a positive value to a negative value around R = 4.1 nm. The linear polarization factor of the dielectric effect is 0.934, independent of radius, as long as the radius remains much less than the electromagnetic wavelength. The result for the two effects shows that the quantum confinement effect gives a correction to the dielectric effect result. It is found that the linear polarization factor of very long (treated approximately as infinitely long) quantum wires is in the range of [0.8, 1]. The linear polarization factors of the quantum confinement effect of CdSe wurtzite quantum wires are calculated for comparison. In the CdSe case, the linear polarization factor of R = 1 nm is 0.857, in agreement with the experimental results (Hu et al 2001 Science 292 2060). This value is much smaller than unity, unlike 0.979 in the GaN case, mainly due to the big spin-orbit splitting energy Δso of CdSe material with wurtzite structure.

  3. Growth of thick GaN layers on laser-processed sapphire substrate by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Koyama, Koji; Aida, Hideo; Kim, Seong-Woo; Ikejiri, Kenjiro; Doi, Toshiro; Yamazaki, Tsutomu

    2014-10-01

    A 600 μm thick GaN layer was successfully grown by hydride vapor phase epitaxy by replacing the standard sapphire substrate with that processed by a focused laser beam within the substrate. The effects of the laser processing on the curvature and cracking of the GaN layer were investigated. Microscopic observations of the interior of the thick GaN layer revealed that the laser-processed substrate suppressed the generation of microcracks in the GaN layer. In addition, the laser processing was also found to reduce the change in the curvature during the GaN layer growth in comparison to that on the standard substrate. It is shown that the overlapping microcracks observed in the GaN layer on the standard sapphire substrate lead to serious cracking after thick GaN layer growth.

  4. MOCVD growth of GaN on Si through novel substrate modification techniques

    NASA Astrophysics Data System (ADS)

    Gagnon, Jarod C.

    GaN is a semiconductor material with great potential for use in high power electronics and optoelectronics due to the high electron mobility, high breakdown voltage, high thermal stability, and large direct bandgap of GaN. Si is a desirable substrate material for GaN heteroepitaxy due to the low cost of production, large wafer sizes available, and current widespread use in the electronics industry. The growth of GaN/Si devices suffers from the lattice and CTE mismatches between GaN and Si and therefore multiple methods of strain reduction have been employed to counter these effects. In this work we presented two novel methods of substrate modification to promote the growth of device quality GaN on Si. Initial work focused on the implantation of AlN/Si(111) substrates with N+ ions below the AlN/Si(111) interface. A reduction in the initial compressive stress in GaN films as well as the degree of tensile stress generation during growth was observed on implanted samples. Optical microscopy of the GaN surfaces showed reduced channeling crack density on implanted substrates. Transmission electron microscopy (TEM) studies showed a disordered layer in the Si substrate at the implantation depth which consisted of a mixture of polycrystalline and amorphous Si. Evidence was provided to suggest that the disordered layer at the implantation depth was acting as a compliant layer which decoupled the GaN film from the bulk Si substrate and partially accommodated the tensile stress formed during growth and cooling. A reduction in threading dislocation (TD) density on ion implanted substrates was also observed. Additional studies showed that by increasing the lateral size of AlN islands, the tensile growth stress and TD density in GaN films on ion implanted substrates could be further reduced. XRD studies showed an expansion of the AlN lattice on implanted substrates with larger lateral island sizes. The final tensile growth stress of films on implanted substrates was further

  5. Dissociated backward priming effects in lexical decision and pronunciation tasks.

    PubMed

    Kahan, T A; Neely, J H; Forsythe, W J

    1999-03-01

    Backward priming was examined at 150- and 500-msec prime-target stimulus onset asynchronies (SOAs) using visually presented primes and targets in lexical decision and pronunciation tasks. Two kinds of backward relations were used: compound items for which targets and primes formed a word in the backward direction (e.g., prime: HOP; target: bell), and noncompound items for which targets and primes did not form a word but were associatively related in the backward but not the forward direction (e.g., prime: BABY; target: stork). Results showed that backward priming effects were equivalent for compounds and noncompounds. However, for lexical decisions, backward priming occurred at both SOAs, whereas for pronunciation, it occurred only at the 150-msec SOA. We discuss how this SOA-dissociated backward priming effect in lexical decision and pronunciation tasks poses a serious challenge for all theories of semantic priming.

  6. H enhancement of N vacancy migration in GaN.

    SciTech Connect

    Wixom, Ryan R.; Wright, Alan Francis

    2005-06-01

    We have used density functional theory to investigate diffusion of V{sub N}{sup +} in the presence of H{sup +}. Optimal migration pathways were determined using the climbing image nudged elastic band and directed dimer methods. Our calculations indicate that the rate-limiting barrier for VN{sub N}{sup +} migration will be reduced by 0.58 eV by interplay with H{sup +}, which will enhance migration by more than an order of magnitude at typical GaN growth temperatures.

  7. Transport mechanisms in Schottky diodes realized on GaN

    NASA Astrophysics Data System (ADS)

    Amor, Sarrah; Ahaitouf, Ali; Ahaitouf, Abdelaziz; Salvestrini, Jean Paul; Ougazzaden, Abdellah

    2017-03-01

    This work is focused on the conducted transport mechanisms involved on devices based in gallium nitride GaN and its alloys. With considering all conduction mechanisms of current, its possible to understanded these transport phenomena. Thanks to this methodology the current-voltage characteristics of structures with unusual behaviour are further understood and explain. Actually, the barrier height (SBH) is a complex problem since it depends on several parameters like the quality of the metal-semiconductor interface. This study is particularly interesting as solar cells are made on this material and their qualification is closely linked to their transport properties.

  8. High field effects of GaN HEMTs.

    SciTech Connect

    Barker, Joy; Shul, Randy John

    2004-09-01

    This report represents the completion of a Laboratory-Directed Research and Development (LDRD) program to develop and fabricate geometric test structures for the measurement of transport properties in bulk GaN and AlGaN/GaN heterostructures. A large part of this study was spent examining fabrication issues related to the test structures used in these measurements, due to the fact that GaN processing is still in its infancy. One such issue had to do with surface passivation. Test samples without a surface passivation, often failed at electric fields below 50 kV/cm, due to surface breakdown. A silicon nitride passivation layer of approximately 200 nm was used to reduce the effects of surface states and premature surface breakdown. Another issue was finding quality contacts for the material, especially in the case of the AlGaN/GaN heterostructure samples. Poor contact performance in the heterostructures plagued the test structures with lower than expected velocities due to carrier injection from the contacts themselves. Using a titanium-rich ohmic contact reduced the contact resistance and stopped the carrier injection. The final test structures had an etch constriction with varying lengths and widths (8x2, 10x3, 12x3, 12x4, 15x5, and 16x4 {micro}m) and massive contacts. A pulsed voltage input and a four-point measurement in a 50 {Omega} environment was used to determine the current through and the voltage dropped across the constriction. From these measurements, the drift velocity as a function of the applied electric field was calculated and thus, the velocity-field characteristics in n-type bulk GaN and AlGaN/GaN test structures were determined. These measurements show an apparent saturation velocity near to 2.5x10{sup 7} cm/s at 180 kV/cm and 3.1x10{sup 7} cm/s, at a field of 140 kV/cm, for the bulk GaN and AlGaN heterostructure samples, respectively. These experimental drift velocities mark the highest velocities measured in these materials to date and confirm

  9. Radiation enhanced basal plane dislocation glide in GaN

    NASA Astrophysics Data System (ADS)

    Yakimov, Eugene B.; Vergeles, Pavel S.; Polyakov, Alexander Y.; Lee, In-Hwan; Pearton, Stephen J.

    2016-05-01

    A movement of basal plane segments of dislocations in GaN films grown by epitaxial lateral overgrowth under low energy electron beam irradiation (LEEBI) was studied by the electron beam induced current (EBIC) method. Only a small fraction of the basal plane dislocation segments were susceptible to irradiation and the movement was limited to relatively short distances. The effect is explained by the radiation enhanced dislocation glide (REDG) in the structure with strong pinning. A dislocation velocity under LEEBI with a beam current lower than 1 nA was estimated as about 10 nm/s. The results assuming the REDG for prismatic plane dislocations were presented.

  10. First-Principles Study of Defects in GaN

    DTIC Science & Technology

    2009-07-29

    energies and other properties of the Gai – VGa and Ni – VN Frenkel pairs in GaN. o Results on the binding energies and stabilities of Frenkel pairs as...Frenkel pair are interstitial Ga ( Gai ) and Ga vacancy (VGa). Gallium interstitial can occur in 3+, 2+, and 1+ charge states, depending on the Fermi...distance to the six Ga nearest neighbors are roughly the same (to within 0.15 Å). The defect level of Gai is found to lie in the upper part of the

  11. Phonon-plasmon coupled modes in GaN

    NASA Astrophysics Data System (ADS)

    Dyson, A.

    2009-04-01

    The phonon lifetime in GaN is known to exhibit a dependence on electron density. Recent noise measurements have also shown the lifetime to be temperature dependent. The source of these dependences is the coupling of the phonon and plasmon populations through the dielectric function. The effect of this anharmonicity is illustrated by comparing the frequency and wavevector dependent coupled-mode momentum relaxation rate with the phonon momentum relaxation rate obtained by Callen. A simple model that includes the anharmonic interaction and phonon migration yields phonon lifetimes depending on both electron density and temperature.

  12. Field emission from quantum size GaN structures

    NASA Astrophysics Data System (ADS)

    Yilmazoglu, O.; Pavlidis, D.; Litvin, Yu. M.; Hubbard, S.; Tiginyanu, I. M.; Mutamba, K.; Hartnagel, H. L.; Litovchenko, V. G.; Evtukh, A.

    2003-12-01

    Whisker structures and quantum dots fabricated by photoelectrochemical (PEC) etching of undoped and doped metalorganic chemical vapor deposition (MOCVD)-grown GaN (2×10 17 or 3×10 18 cm -3) are investigated in relation with their field-emission characteristics. Different surface morphologies, corresponding to different etching time and photocurrent, results in different field-emission characteristics with low turn-on voltage down to 4 V/μm and the appearance of quantum-size effect in the I- V curves.

  13. Modelling of GaN quantum dot terahertz cascade laser

    NASA Astrophysics Data System (ADS)

    Asgari, A.; Khorrami, A. A.

    2013-03-01

    In this paper GaN based spherical quantum dot cascade lasers has been modelled, where the generation of the terahertz waves are obtained. The Schrödinger, Poisson, and the laser rate equations have been solved self-consistently including all dominant physical effects such as piezoelectric and spontaneous polarization in nitride-based QDs and the effects of the temperature. The exact value of the energy levels, the wavefunctions, the lifetimes of electron levels, and the lasing frequency are calculated. Also the laser parameters such as the optical gain, the output power and the threshold current density have been calculated at different temperatures and applied electric fields.

  14. Photoluminescence enhancement from GaN by beryllium doping

    NASA Astrophysics Data System (ADS)

    García-Gutiérrez, R.; Ramos-Carrazco, A.; Berman-Mendoza, D.; Hirata, G. A.; Contreras, O. E.; Barboza-Flores, M.

    2016-10-01

    High quality Be-doped (Be = 0.19 at.%) GaN powder has been grown by reacting high purity Ga diluted alloys (Be-Ga) with ultra high purity ammonia in a horizontal quartz tube reactor at 1200 °C. An initial low-temperature treatment to dissolve ammonia into the Ga melt produced GaN powders with 100% reaction efficiency. Doping was achieved by dissolving beryllium into the gallium metal. The powders synthesized by this method regularly consist of two particle size distributions: large hollow columns with lengths between 5 and 10 μm and small platelets in a range of diameters among 1 and 3 μm. The GaN:Be powders present a high quality polycrystalline profile with preferential growth on the [10 1 bar 1] plane, observed by means of X-ray diffraction. The three characteristics growth planes of the GaN crystalline phase were found by using high resolution TEM microscopy. The optical enhancing of the emission in the GaN powder is attributed to defects created with the beryllium doping. The room temperature photoluminescence emission spectra of GaN:Be powders, revealed the presence of beryllium on a shoulder peak at 3.39 eV and an unusual Y6 emission at 3.32eV related to surface donor-acceptor pairs. Also, a donor-acceptor-pair transition at 3.17 eV and a phonon replica transition at 3.1 eV were observed at low temperature (10 K). The well-known yellow luminescence band coming from defects was observed in both spectra at room and low temperature. Cathodoluminescence emission from GaN:Be powders presents two main peaks associated with an ultraviolet band emission and the yellow emission known from defects. To study the trapping levels related with the defects formed in the GaN:Be, thermoluminescence glow curves were obtained using UV and β radiation in the range of 50 and 150 °C.

  15. A modeling study of GaN growth by MOVPE

    SciTech Connect

    Safvi, S.A.; Kuech, T.F.; Redwing, J.M.; Tischler, M.A.

    1996-11-01

    A model for the growth of gallium nitride in a vertical metalorganic vapor phase epitaxy reactor is presented. For a mixture of non-dilute gases, the flow temperature and concentration profiles are predicted. The results show that the growth of GaN epilayers is through an intermediate adduct of TMG and ammonia. Growth rates are predicted based on simple reaction mechanisms and compared with those obtained experimentally. Loss of adduct species due to polymerization leads to lowering in growth rate. An attempt to quantify loss of reacting species is made based on experimentally observed growth rates.

  16. The PRISM/PRIME Project

    NASA Astrophysics Data System (ADS)

    Barlow, R. J.

    2011-09-01

    Lepton Flavour violation is predicted by many theories beyond the standard model. In the muon sector such a violation entails not only direct μ→eγ decay but also the conversion process μ→e. To measure this to high precision requires a large number of muons of very similar energy, and this is difficult to achieve from a muon target with conventional beam optics. PRISM is an FFAG system designed to accept large numbers of muons ( 10/sec) with a wide range of energies, and render them monochromatic by accelerating the less energetic muons and decelerating the more energetic ones. To preserve Liouville's theorem, this is accompanied by a broadening in the timing of the muons, hence the name 'Phase Rotated Intense Slow Muon source.' The principles of this device have been demonstrated and components prototyped. PRIME is a detector (PRISM Muon Electron Conversion) which has been designed to stop 20 MeV bunches of muons in a thin foil, giving a very clean signal and reaching a background sensitivity of 10, four orders of magnitude better than today's limits and probing the interesting region for BSM theories.

  17. GaN quantum dot polarity determination by X-ray photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Romanyuk, O.; Bartoš, I.; Brault, J.; Mierry, P. De; Paskova, T.; Jiříček, P.

    2016-12-01

    Growth of GaN quantum dots (QDs) on polar and semipolar GaN substrates is a promising technology for efficient nitride-based light emitting diodes (LED). The QDs crystal orientation typically repeats the polarity of the substrate. In case of non-polar or semipolar substrates, the polarity of QDs is not obvious. In this article, the polarity of GaN QDs and of underlying layers was investigated nondestructively by X-ray photoelectron diffraction (XPD). Polar and semipolar GaN/Al0.5Ga0.5N heterostructures were grown on the sapphire substrates with (0001) and (1 1 bar 00) orientations by molecular beam epitaxy (MBE). Polar angle dependence of N 1s core-level photoelectron intensities were measured from GaN QDs and compared with the corresponding experimental curves from free-standing GaN crystals. It is confirmed experimentally, that the crystalline orientation of polar (0001) GaN QDs follows the orientation of the (0001) sapphire substrate. In case of semipolar GaN QDs grown on (1 1 bar 00) sapphire substrate, the (11 2 bar 2) polarity of QDs was determined.

  18. Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy.

    PubMed

    Zhong, Aihua; Hane, Kazuhiro

    2012-12-27

    GaN nanowall network was epitaxially grown on Si (111) substrate by molecular beam epitaxy. GaN nanowalls overlap and interlace with one another, together with large numbers of holes, forming a continuous porous GaN nanowall network. The width of the GaN nanowall can be controlled, ranging from 30 to 200 nm by adjusting the N/Ga ratio. Characterization results of a transmission electron microscope and X-ray diffraction show that the GaN nanowall is well oriented along the C axis. Strong band edge emission centered at 363 nm is observed in the spectrum of room temperature photoluminescence, indicating that the GaN nanowall network is of high quality. The sheet resistance of the Si-doped GaN nanowall network along the lateral direction was 58 Ω/. The conductive porous nanowall network can be useful for integrated gas sensors due to the large surface area-to-volume ratio and electrical conductivity along the lateral direction by combining with Si micromachining.

  19. Photoelectrochemical water splitting on nanoporous GaN thin films for energy conversion under visible light

    NASA Astrophysics Data System (ADS)

    Cao, Dezhong; Xiao, Hongdi; Fang, Jiacheng; Liu, Jianqiang; Gao, Qingxue; Liu, Xiangdong; Ma, Jin

    2017-01-01

    Nanoporous (NP) GaN thin films, which were fabricated by an electrochemical etching method at different voltages, were used as photoelectrodes during photoelectrochemical (PEC) water splitting in 1 M oxalic acid solution. Upon illumination at a power density of 100 mW cm‑2 (AM 1.5), water splitting is observed in NP GaN thin films, presumably resulting from the valence band edge which is more positive than the redox potential of the oxidizing species. In comparison with NP GaN film fabricated at 8 V, NP GaN obtained at 18 V shows nearly twofold enhancement in photocurrent with the maximum photo-to-hydrogen conversion efficiency of 1.05% at ~0 V (versus Ag/AgCl). This enhancement could be explained with (i) the increase of surface area and surface states, and (ii) the decrease of resistances and carrier concentration in the NP GaN thin films. High stability of the NP GaN thin films during the PEC water splitting further confirms that the NP GaN thin film could be applied to the design of efficient solar cells and solar fuel devices.

  20. Fabrication of photonic crystal circuits based on GaN ultrathin membranes by maskless lithography

    NASA Astrophysics Data System (ADS)

    Volciuc, Olesea; Braniste, Tudor; Sergentu, Vladimir; Ursaki, Veaceslav; Tiginyanu, Ion M.; Gutowski, Jürgen

    2015-06-01

    We report on maskless fabrication of photonic crystal (PhC) circuits based on ultrathin (d ~ 15 nm) nanoperforated GaN membranes exhibiting a triangular lattice arrangement of holes with diameters of 150 nm. In recent years, we have proposed and developed a cost-effective technology for GaN micro- and nanostructuring, the so-called surface charge lithography (SCL), which opened wide possibilities for a controlled fabrication of GaN ultrathin membranes. SCL is a maskless approach based on direct writing of negative charges on the surface of a semiconductor by a focused ion beam (FIB). These charges shield the material against photo-electrochemical (PEC) etching. Ultrathin GaN membranes suspended on specially designed GaN microstructures have been fabricated using a technological route based on SCL with two selected doses of ion beam treatment. Calculation of the dispersion law in nanoperforated membranes in the approximation of scalar waves is indicative of the occurrence of surface and bulk modes, and there is a range of frequencies where only surface modes can exist. Advantages of the occurrence of two types of modes in ultrathin nanoperforated GaN membranes from the point of view of their incorporation in photonic and optoelectronic integrated circuits are discussed. Along with this, we present the results of a comparative analysis of persistent photoconductivity (PPC) and optical quenching (OQ) effects occurring in continuous and nanoperforated ultrathin GaN suspended membranes, and assess the mechanisms behind these phenomena.

  1. Theoretical study for heterojunction surface of NEA GaN photocathode dispensed with Cs activation

    NASA Astrophysics Data System (ADS)

    Xia, Sihao; Liu, Lei; Wang, Honggang; Wang, Meishan; Kong, Yike

    2016-09-01

    For the disadvantages of conventional negative electron affinity (NEA) GaN photocathodes activated by Cs or Cs/O, new-type NEA GaN photocathodes with heterojunction surface dispensed with Cs activation are investigated based on first-principle study with density functional theory. Through the growth of an ultrathin n-type GaN cap layer on p-type GaN emission layer, a p-n heterojunction is formed on the surface. According to the calculation results, it is found that Si atoms tend to replace Ga atoms to result in an n-type doped cap layer which contributes to the decreasing of work function. After the growth of n-type GaN cap layer, the atom structure near the p-type emission layer is changed while that away from the surface has no obvious variations. By analyzing the E-Mulliken charge distribution of emission surface with and without cap layer, it is found that the positive charge of Ga and Mg atoms in the emission layer decrease caused by the cap layer, while the negative charge of N atom increases. The conduction band moves downwards after the growth of cap layer. Si atom produces donor levels around the valence band maximum. The absorption coefficient of GaN emission layer decreases and the reflectivity increases caused by n-type GaN cap layer.

  2. Fabrication of GaN nanotubular material using MOCVD with aluminum oxide membrane

    NASA Astrophysics Data System (ADS)

    Jung, Woo-Gwang; Jung, Se-Hyuck; Kung, Patrick; Razeghi, Manijeh

    2006-02-01

    GaN nanotubular material is fabricated with aluminum oxide membrane in MOCVD. SEM, XRD, TEM and PL are employed to characterize the fabricated GaN nanotubular material. An aluminum oxide membrane with ordered nano holes is used as template. Gallium nitride is deposited at the inner wall of the nano holes in aluminum oxide template, and the nanotubular material with high aspect ratio is synthesized using the precursors of TMG and ammonia gas. Optimal synthesis condition in MOCVD is obtained successfully for the gallium nitride nanotubular material in this research. The diameter of GaN nanotube fabricated is approximately 200 ~ 250 nm and the wall thickness is about 40 ~ 50 nm. GaN nanotubular material consists of numerous fine GaN particulates with sizes ranging 15 to 30 nm. The composition of gallium nitride is confirmed to be stoichiometrically 1:1 for Ga and N by EDS. XRD and TEM analyses indicate that grains in GaN nanotubular material have nano-crystalline structure. No blue shift is found in the PL spectrum on the GaN nanotubular material fabricated in aluminum oxide template.

  3. Fabrication of GaN nanotubular material using MOCVD with an aluminium oxide membrane

    NASA Astrophysics Data System (ADS)

    Jung, Woo-Gwang; Jung, Se-Hyuck; Kung, Patrick; Razeghi, Manijeh

    2006-01-01

    GaN nanotubular material is fabricated with an aluminium oxide membrane in MOCVD. SEM, XRD, TEM and PL are employed to characterize the fabricated GaN nanotubular material. An aluminium oxide membrane with ordered nanoholes is used as a template. Gallium nitride is deposited at the inner wall of the nanoholes in the aluminium oxide template, and the nanotubular material with high aspect ratio is synthesized using the precursors of TMG and ammonia gas. Optimal synthesis conditions in MOCVD are obtained successfully for the gallium nitride nanotubular material in this research. The diameter of the GaN nanotube fabricated is approximately 200-250 nm and the wall thickness is about 40-50 nm. GaN nanotubular material consists of numerous fine GaN particulates with size range 15-30 nm. The composition of gallium nitride is confirmed to be stoichiometrically 1:1 for Ga and N by EDS. XRD and TEM analyses indicate that the grains in GaN nanotubular material have a nano-crystalline structure. No blue shift is found in the PL spectrum on the GaN nanotubular material fabricated in an aluminium oxide template.

  4. Air-bridged lateral epitaxial overgrowth of GaN thin films

    NASA Astrophysics Data System (ADS)

    Kidoguchi, Isao; Ishibashi, Akihiko; Sugahara, Gaku; Ban, Yuzaburoh

    2000-06-01

    A promising technique of selective lateral epitaxy, namely air-bridged lateral epitaxial overgrowth, is demonstrated in order to reduce the wing tilt as well as the threading dislocation density in GaN thin films. A seed GaN layer was etched to make ridge-stripe along <11¯00>GaN direction and a GaN material was regrown from the exposed (0001) top facet of the ridged GaN seed structures, whose sidewalls and etched bottoms were covered with silicon nitride mask, using low-pressure metalorganic vapor phase epitaxy. The density of dislocations in the wing region was reduced to be <107cm-2, which was at least two orders of magnitude lower than that of underlying GaN. The magnitude of the wing tilt was determined to be 0.08° by x-ray diffraction (XRD) measurements, which was smaller than other lateral epitaxial overgrown GaN thin films. The full width at half maximum of XRD for the wing region was 138 arc sec, indicating high uniformity of c-axis orientation.

  5. Mediated priming in the cerebral hemispheres.

    PubMed

    Livesay, Kay; Burgess, Curt

    2003-11-01

    The present experiment investigates hemispheric differences in mediated priming. Theories of lexical representation have argued for an asymmetrical coding between the right and left hemispheres ([Beeman, 1998]), claiming that the right hemisphere is more diffusely represented compared to the left hemisphere. Thus, the right hemisphere activates a larger semantic field compared to the left hemisphere. Mediated (two-step) priming is an ideal task to examine this representational claim, because of the distant nature of the prime-target pairs. Results showed no difference in the magnitude of priming (both mediated and direct) between the right and left hemispheres. These results suggest that the lexical representation of the two hemispheres is equivalent, not asymmetrical as Beeman suggests.

  6. Preserved conceptual priming in Alzheimer's disease.

    PubMed

    Martins, Carla A R; Lloyd-Jones, Toby J

    2006-10-01

    We assessed Alzheimer's disease (AD) and healthy older adult control (HC) group performance on: (1) a conceptual priming task, in which participants had to make a semantic decision as to whether a degraded picture of an object encountered previously belonged to the category of living or non-living things; and (2) a recognition memory task. The AD group showed a dissociation between impaired performance on the recognition task and preserved priming for semantic decisions to degraded pictures. We argue that it is not whether priming is conceptual or perceptual that is important for the observation of priming in AD, rather it is the nature of the response that is required (c.f., Gabrieli et al., 1999).

  7. Negative Priming in Free Recall Reconsidered

    PubMed Central

    2015-01-01

    Negative priming in free recall is the finding of impaired memory performance when previously ignored auditory distracters become targets of encoding and retrieval. This negative priming has been attributed to an aftereffect of deploying inhibitory mechanisms that serve to suppress auditory distraction and minimize interference with learning and retrieval of task-relevant information. In 6 experiments, we tested the inhibitory account of the effect of negative priming in free recall against alternative accounts. We found that ignoring auditory distracters is neither sufficient nor necessary to produce the effect of negative priming in free recall. Instead, the effect is more readily accounted for by a buildup of proactive interference occurring whenever 2 successively presented lists of words are drawn from the same semantic category. PMID:26595066

  8. Russian Prime Minister Calls the Station Crew

    NASA Video Gallery

    Russian Prime Minister Vladimir Putin called the International Space Station from the Russian Mission Control Center in Korolev, Russia, on Jan. 11, 2011. Putin also offered his condolences to ISS ...

  9. NASA and OPTIMUS PRIME Team Up

    NASA Video Gallery

    NASA and OPTIMUS PRIME have teamed up to educate! Kids everywhere created videos showing how NASA technology is truly more than meets the eye, and now you can vote on your favorite! Visit http://ip...

  10. OVATION Prime Model and "Aurorasaurus" Auroral Observations

    NASA Video Gallery

    This video shows the auroral oval, as modeled using OVATION Prime (2013), along with citizen science reports collected by the Aurorasaurus project for the St. Patrick’s Day storm over March 17-19, ...

  11. Degree of handedness and priming: further evidence for a distinction between production and identification priming mechanisms.

    PubMed

    LaVoie, Donna J; Olbinski, Brianna; Palmer, Shayna

    2015-01-01

    The distinction between implicit and explicit forms of memory retrieval is long-standing, and important to the extent it reveals how different neural architecture supports different aspects of memory function. Similarly, distinctions have been made between kinds of repetition priming, a form of implicit memory retrieval. This study focuses on the production-identification (ID) priming distinction, which delineates priming tasks involving verification of stimulus features as compared to priming tasks that require use of a cue to guide response retrieval. Studies investigating this dissociation in dementia or similar patient populations indicate that these forms of priming may differ in their neural bases. The current study looks at degree of handedness as a way of investigating inferred neural architecture supporting these two forms of priming. A growing body of research indicates that degree of handedness (consistent, or CH, versus inconsistent, or ICH) is associated with greater interhemispheric interaction and functional access to right hemisphere processing in ICH, with superior performance seen in ICH on memory tasks reliant on this processing. Arguments about the theoretical mechanisms underlying ID and production forms of perceptual priming tasks suggest that performance on these tasks will differ as a function of degree of handedness. We tested this question in a group of CH and ICH young adults, who were asked to study lists of words prior to performing a production priming task (word stem completion, WSC), a perceptual word ID task, and a word stem cued recall task. While both handedness groups exhibited reliable priming across tasks, WSC priming was greater in ICH than CH participants, with ID priming not differing between groups. This dissociation supports the argument that production and ID forms of priming have different underlying neural bases.

  12. Ground-based radar reflectivity mosaic of mei-yu precipitation systems over the Yangtze River-Huaihe River basins

    NASA Astrophysics Data System (ADS)

    Luo, Yali; Qian, Weimiao; Gong, Yu; Wang, Hongyan; Zhang, Da-Lin

    2016-11-01

    The 3D radar reflectivity produced by a mosaic software system, with measurements from 29 operational weather radars in the Yangtze River-Huaihe River Basins (YRHRB) during the mei-yu season of 2007, is compared to coincident TRMM PR observations in order to evaluate the value of the ground-based radar reflectivity mosaic in characterizing the 3D structures of mei-yu precipitation. Results show reasonable agreement in the composite radar reflectivity between the two datasets, with a correlation coefficient of 0.8 and a mean bias of -1 dB. The radar mosaic data at constant altitudes are reasonably consistent with the TRMM PR observations in the height range of 2-5 km, revealing essentially the same spatial distribution of radar echo and nearly identical histograms of reflectivity. However, at altitudes above 5 km, the mosaic data overestimate reflectivity and have slower decreasing rates with height compared to the TRMM PR observations. The areas of convective and stratiform precipitation, based on the mosaic reflectivity distribution at 3-km altitude, are highly correlated with the corresponding regions in the TRMM products, with correlation coefficients of 0.92 and 0.97 and mean relative differences of -7.9% and -2.5%, respectively. Finally, the usefulness of the mosaic reflectivity at 3-km altitude at 6-min intervals is illustrated using a mesoscale convective system that occurred over the YRHRB.

  13. Spectroscopic and photophysical properties of complexes of 4{prime}-ferrocenyl-2,2{prime}:6{prime},2{double_prime}-terpyridine and related ligands

    SciTech Connect

    Hutchinson, K.; Morris, J.C.; Nile, T.A.; Walsh, J.L.; Thompson, D.W.; Petersen, J.D.; Schoonover, J.R.

    1999-05-17

    4{prime}-(Ferrocenyl)-2,2{prime}:6{prime}2{double_prime}-terpyridine (Fctpy) and 4{prime}-(4-pyridyl)-2,2{prime}:6{prime},2{double_prime}-terpyridine (pytpy) were prepared from the corresponding ferrocene- and pyridinecarboxaldehyle and 2-acetylpyridine using the Krohnke synthetic methodology. Metal complexes, [M(Fctpy){sub 2}](PF{sub 6}){sub 2} (M = Ru, Fe, Zn), [Ru(tpy)(Fctpy)](PF{sub 6}){sub 2} (tpy = 2,2{prime}:6{prime},6{double_prime}-terpyridine), and [Ru(pytpy){sub 2}](PF{sub 6}){sub 2} were prepared and characterized. Cyclic voltammetric analysis indicated Ru(III/II) and ferrocenium/ferrocene redox couples near expected potentials (Ru{sup III/II} {approximately}1.3 V and ferrocenium/ferrocene {approximately}0.6 V vs Ag/AgCl). In addition to dominant {pi}{sub tpy} {r_arrow} {pi}{sub tpy}{sup *} UV absorptions near 240 and 280 nm and d{sub {pi}}{sup Ru} {r_arrow} {pi}{sub tpy}{sup *} MLCT absorptions around 480 nm, the complexes [Ru(Fctpy){sub 2}](PF{sub 6}){sub 2} and [Ru(tpy)(Fctpy)](PF{sub 6}){sub 2} exhibit an unusual absorption band around 530 nm. Resonance Raman measurements indicate that this band is due to a {sup 1}[(d({pi}){sub Fc}){sup 6}] {r_arrow} {sup 1}[(d({pi}){sub Fc}){sup 5}({pi}{sup *}{sub tpy}{sup Ru}){sup 1}] transition. For [Ru(Fctpy){sub 2}](PF{sub 6}){sub 2} and [Ru(tpy)(Fctpy)](PF{sub 6}){sub 2}, excited-state emission and lifetime measurements indicated an upper-limit emission quantum yield of 0.003 and an upper-limit emission lifetime of 0.025 {micro}s. The influence of the ferrocenyl site on excited-state decay is discussed, and an excited-state energy level diagram is proposed.

  14. Periodicity In The Intervals Between Primes

    DTIC Science & Technology

    2015-07-02

    statistically strong periodicity is identified in the counting function giving the total number of intervals of a certain size. The nature of the periodic...positive intervals among the first n<=10^6 prime numbers as a probe of the global nature of the sequence of primes. A statistically strong periodicity is...Let x = x1, x2, . . . be an increasing sequence of real numbers which may be either finite or infinitely long. Throughout the following every bold

  15. Integrative Priming of Compositional and Locative Relations

    PubMed Central

    Jones, Lara L.; Wurm, Lee H.; Calcaterra, Ryan D.; Ofen, Noa

    2017-01-01

    Integrative priming refers to the facilitated recognition of a target word (bench) as a real word following a prime (park). Prior integrative priming studies have used a wide variety of integrative relations including temporal (summer rain), topical (travel book), locative (forest river), and compositional (peach pie) relations. Yet differences in the types of integrative relations may yield differences in the underlying explanatory processes of integrative priming. In this study, we compared the magnitude, time course, and three theoretically based correlates of integrative priming for compositional (stone table) and locative (patio table) pairs in a lexical decision task across four stimulus onset asynchronies (SOAs; 50, 300, 800, and 1,600 ms). Based on the Complementary Role Activation theory, integrative ratings (the extent to which the prime and target can be combined into a meaningful phrase) were predicted to facilitate target RTs. Based on the Embodied Conceptual Combination (ECCo) theory, the local co-occurrence of the prime and target, and the ability to perceptually simulate (visually experience) the prime-target pair were tested as predictors. In comparison to unrelated pairs (nose table), target RTs were faster for the compositional and locative pairs, though did not differ between these relations. In support of the Complementary Role Activation theory, integrative ratings predicted target RTs above and beyond our control variables. In support of the ECCo theory, co-occurrence emerged as an early predictor of target RTs, and visual experience ratings was a reliable predictor at the 300 ms SOA, though only for the compositional relations. PMID:28360872

  16. Ga vacancy induced ferromagnetism enhancement and electronic structures of RE-doped GaN

    NASA Astrophysics Data System (ADS)

    Zhong, Guohua; Zhang, Kang; He, Fan; Ma, Xuhang; Lu, Lanlan; Liu, Zhuang; Yang, Chunlei

    2012-09-01

    Because of their possible applications in spintronic and optoelectronic devices, GaN dilute magnetic semiconductors (DMSs) doped by rare-earth (RE) elements have attracted much attention since the high Curie temperature was obtained in RE-doped GaN DMSs and a colossal magnetic moment was observed in the Gd-doped GaN thin film. We have systemically studied the GaN DMSs doped by RE elements (La, Ce-Yb) using the full-potential linearized augmented plane wave method within the framework of density functional theory and adding the considerations of the electronic correlation and the spin-orbital coupling effects. We have studied the electronic structures of DMSs, especially for the contribution from f electrons. The origin of magnetism, magnetic interaction and the possible mechanism of the colossal magnetic moment were explored. We found that, for materials containing f electrons, electronic correlation was usually strong and the spin-orbital coupling was sometimes crucial in determining the magnetic ground state. It was found that GaN doped by La was non-magnetic. GaN doped by Ce, Nd, Pm, Eu, Gd, Tb and Tm are stabilized at antiferromagnetic phase, while GaN doped by other RE elements show strong ferromagnetism which is suitable materials for spintronic devices. Moreover, we have identified that the observed large enhancement of magnetic moment in GaN is mainly caused by Ga vacancies (3.0μB per Ga vacancy), instead of the spin polarization by magnetic ions or originating from N vacancies. Various defects, such as substitutional Mg for Ga, O for N under the RE doping were found to bring a reduction of ferromagnetism. In addition, intermediate bands were observed in some systems of GaN:RE and GaN with intrinsic defects, which possibly opens the potential application of RE-doped semiconductors in the third generation high efficiency photovoltaic devices.

  17. Annealing effects on polycrystalline GaN using nitrogen and ammonia ambients

    NASA Astrophysics Data System (ADS)

    Ariff, A.; Zainal, N.; Hassan, Z.

    2016-09-01

    This paper describes effects of using post-annealing treatment in different conditions on the properties of polycrystalline GaN layer grown on m-plane sapphire substrate by electron beam (e-beam) evaporator. Without annealing, GaN surface was found to have a low RMS roughness with agglomeration of GaN grains in a specific direction and the sample consisted of gallium oxide (Ga2O3) material. When the post-annealing treatment was carried out in N2 ambient at 650 °C, initial re-crystallization of the GaN grains was observed while the evidence of Ga2O3 almost disappeared. As the NH3 annealing was conducted at 950 °C, more effect of re-crystallization occurred but with less grains coalescence. Three dominant XRD peaks of GaN in (10 1 bar 0) , (0002) and (10 1 bar 1) orientations were evident. Near band edge (NBE) related emission in GaN was also observed. The significant improvement was attributed to simultaneous recrystallization and effective reduction of N deficiency density. The post-annealing in a mixture of N2 and NH3 ambient at 950 °C was also conducted, but has limited the effectiveness of the N atoms to incorporate on the GaN layer due to 'clouding' effect by the inert N2 gas. Further increase in the annealing temperature at 980 °C and 1100 °C, respectively caused severe deteriorations of the structural and optical properties of the GaN layer. Overall, this work demonstrated initial potential in improving polycrystalline GaN material in simple and inexpensive manner.

  18. On the relation between conceptual priming, neural priming, and novelty assessment.

    PubMed

    Habib, R

    2001-07-01

    A consistently reported finding in functional neuroimaging studies which compare processing of new information to processing of old information is a reduction in blood flow, and hence neural activity, associated with the old condition. This deactivation has been labeled neural priming. Some investigators have hypothesized that neural priming is the physiological mechanism underlying conceptual priming--a facilitation in the semantic processing of repeated information. Others, however, have hypothesized that neural priming reflects novelty assessment--a mechanism which minimizes the probability that redundant information will be stored in long-term memory. In this paper, the conceptual priming and novelty assessment hypotheses are compared and contrasted in order to ask, and tentatively answer, the question: Are conceptual priming and novelty assessment cognitively and neurophysiologically distinct? Based on a review of the literature, it is suggested that whereas novelty assessment and conceptual priming are distinct cognitive entities, they cannot be presently separated neurophysiologically. That is, some novelty assessment deactivations may in fact reflect priming, and some priming deactivations may in fact reflect novelty assessment.

  19. Non-cognate translation priming in masked priming lexical decision experiments: A meta-analysis.

    PubMed

    Wen, Yun; van Heuven, Walter J B

    2016-09-09

    The masked translation priming paradigm has been widely used in the last 25 years to investigate word processing in bilinguals. Motivated by studies reporting mixed findings, in particular for second language (L2) to first language (L1) translation priming, we conducted, for the first time in the literature, a meta-analysis of 64 masked priming lexical decision experiments across 24 studies to assess the effect sizes of L1-L2 and L2-L1 non-cognate translation priming effects in bilinguals. Our meta-analysis also investigated the influence of potential moderators of translation priming effects. The results provided clear evidence of significant translation priming effects for both directions, with L1-L2 translation priming significantly larger than L2-L1 translation priming (i.e., effect size of 0.86 vs. 0.31). The analyses also revealed that L1-L2 translation effect sizes were moderated by the interval between prime and target (ISI), whereas L2-L1 translation effect sizes were modulated by the number of items per cell. Theoretical and methodological implications of this meta-analysis are discussed and recommendations for future studies are provided.

  20. Priming addition facts with semantic relations.

    PubMed

    Bassok, Miriam; Pedigo, Samuel F; Oskarsson, An T

    2008-03-01

    Results from 2 relational-priming experiments suggest the existence of an automatic analogical coordination between semantic and arithmetic relations. Word pairs denoting object sets served as primes in a task that elicits "obligatory" activation of addition facts (5 + 3 activates 8; J. LeFevre, J. Bisanz, & L. Mrkonjic, 1988). Semantic relations between the priming words were either aligned or misaligned with the structure of addition (M. Bassok, V. M. Chase, & S. A. Martin, 1998). Obligatory activation of addition facts occurred when the digits were primed by categorically related words (tulips-daisies), which are aligned with addition, but did not occur when the digits were primed by unrelated words (hens-radios, Experiment 1) or by functionally related words (records-songs, Experiment 2), which are misaligned with addition. These findings lend support to the viability of automatic analogical priming (B. A. Spellman, K. J. Holyoak, & R. G. Morrison, 2001) and highlight the relevance of arithmetic applications to theoretical accounts of mental arithmetic.

  1. Conditional discriminations, symmetry, and semantic priming.

    PubMed

    Vaidya, Manish; Hudgins, Caleb D; Ortu, Daniele

    2015-09-01

    Psychologists interested in the study of symbolic behavior have found that people are faster at reporting that two words are related to one another than they are in reporting that two words are not related - an effect called semantic priming. This phenomenon has largely been documented in the context of natural languages using real words as stimuli. The current study asked whether laboratory-generated stimulus-stimulus relations established between arbitrary geometrical shapes would also show the semantic priming effect. Participants learned six conditional relations using a one-to-many training structure (A1-B1, A1-C1, A1-D1, A2-B2, A2-C2, A2-D2) and demonstrated, via accurate performance on tests of derived symmetry, that the trained stimulus functions had become reversible. In a lexical decision task, subjects also demonstrated a priming effect as they displayed faster reaction times to target stimuli when the prime and target came from the same trained or derived conditional relations, compared to the condition in which the prime and target came from different trained or derived conditional relations. These data suggest that laboratory-generated equivalence relations may serve as useful analogues of symbolic behavior. However, the fact that conditional relations training and symmetry alone were sufficient to produce the effect suggests that semantic priming like effects may be the byproduct of simpler stimulus-stimulus relations.

  2. Growth of GaN nanotubes and nanowires

    NASA Astrophysics Data System (ADS)

    He, Maoqi; Zhou, Piezhen; Mohammad, S. Noor; Halpern, Joshua; Jacobs, Randy; Sarney, Wendy; Salamanca-Riba, Lourdes

    2001-03-01

    We have grown GaN nanowires and nanotubes by direct reaction of Ga metal vapor with NH3 in a simple tube furnace. By varying the ammonia flow rate (20-120 sccm) and temperature (800-1000 ^oC) we have been able to control onset of growth, and the diameters of these cylindrically symmetric nanostructures. The length of the nanowires and nanotubes is determined by the duration of the growth cycle. The nanowires and nanotubes that we have studied are single crystal and have a wurtzite structure. In the first 90 minutes, a 1 or 2 μ thick amorphous GaN matrix is deposited. Soon after pebble like polycrystalline hillocks form. Single crystal nanowires sprout from the sides of the platelets. The diameter of the nanowire is the same as the thickness of the plate, that is the smallest dimension of the face from which it grows. Since the platelet thickness depends on temperature and the ammonia, the thickness of the nanowires is proportional to the temperature and ammonia flow rate. At higher temperatures and flow rates nanotubes and rods start to grow from the flat surface of the plates

  3. Magneto-ballistic transport in GaN nanowires

    NASA Astrophysics Data System (ADS)

    Santoruvo, Giovanni; Allain, Adrien; Ovchinnikov, Dmitry; Matioli, Elison

    2016-09-01

    The ballistic filtering property of nanoscale crosses was used to investigate the effect of perpendicular magnetic fields on the ballistic transport of electrons on wide band-gap GaN heterostructures. The straight scattering-less trajectory of electrons was modified by a perpendicular magnetic field which produced a strong non-linear behavior in the measured output voltage of the ballistic filters and allowed the observation of semi-classical and quantum effects, such as quenching of the Hall resistance and manifestation of the last plateau, in excellent agreement with the theoretical predictions. A large measured phase coherence length of 190 nm allowed the observation of universal quantum fluctuations and weak localization of electrons due to quantum interference up to ˜25 K. This work also reveals the prospect of wide band-gap GaN semiconductors as a platform for basic transport and quantum studies, whose properties allow the investigation of ballistic transport and quantum phenomena at much larger voltages and temperatures than in other semiconductors.

  4. Orthodox etching of HVPE-grown GaN

    SciTech Connect

    Weyher, J.L.; Lazar, S.; Macht, L.; Liliental-Weber, Z.; Molnar,R.J.; Muller, S.; Nowak, G.; Grzegory, I.

    2006-08-10

    Orthodox etching of HVPE-grown GaN in molten eutectic of KOH + NaOH (E etch) and in hot sulfuric and phosphoric acids (HH etch) is discussed in detail. Three size grades of pits are formed by the preferential E etching at the outcrops of threading dislocations on the Ga-polar surface of GaN. Using transmission electron microscopy (TEM) as the calibration tool it is shown that the largest pits are formed on screw, intermediate on mixed and the smallest on edge dislocations. This sequence of size does not follow the sequence of the Burgers values (and thus the magnitude of the elastic energy) of corresponding dislocations. This discrepancy is explained taking into account the effect of decoration of dislocations, the degree of which is expected to be different depending on the lattice deformation around the dislocations, i.e. on the edge component of the Burgers vector. It is argued that the large scatter of optimal etching temperatures required for revealing all three types of dislocations in HVPE-grown samples from different sources also depends upon the energetic status of dislocations. The role of kinetics for reliability of etching in both etches is discussed and the way of optimization of the etching parameters is shown.

  5. High Quality, Low Cost Ammonothermal Bulk GaN Substrates

    SciTech Connect

    Ehrentraut, D; Pakalapati, RT; Kamber, DS; Jiang, WK; Pocius, DW; Downey, BC; McLaurin, M; D'Evelyn, MP

    2013-12-18

    Ammonothermal GaN growth using a novel apparatus has been performed on c-plane, m-plane, and semipolar seed crystals with diameters between 5 mm and 2 in. to thicknesses of 0.5-3 mm. The highest growth rates are greater than 40 mu m/h and rates in the 10-30 mu m/h range are routinely observed for all orientations. These values are 5-100x larger than those achieved by conventional ammonothermal GaN growth. The crystals have been characterized by X-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), optical spectroscopy, and capacitance-voltage measurements. The crystallinity of the grown crystals is similar to or better than that of the seed crystals, with FWHM values of about 20-100 arcsec and dislocation densities of 1 x 10(5)-5 x 10(6) cm(-2). Dislocation densities below 10(4) cm(-2) are observed in laterally-grown crystals. Epitaxial InGaN quantum well structures have been successfully grown on ammonothermal wafers. (C) 2013 The Japan Society of Applied Physics

  6. Europium doping of zincblende GaN by ion implantation

    SciTech Connect

    Lorenz, K.; Franco, N.; Darakchieva, V.; Alves, E.; Roqan, I. S.; O'Donnell, K. P.; Trager-Cowan, C.; Martin, R. W.; As, D. J.; Panfilova, M.

    2009-06-01

    Eu was implanted into high quality cubic (zincblende) GaN (ZB-GaN) layers grown by molecular beam epitaxy. Detailed structural characterization before and after implantation was performed by x-ray diffraction (XRD) and Rutherford backscattering/channeling spectrometry. A low concentration (<10%) of wurtzite phase inclusions was observed by XRD analysis in as-grown samples with their (0001) planes aligned with the (111) planes of the cubic lattice. Implantation of Eu causes an expansion of the lattice parameter in the implanted region similar to that observed for the c-lattice parameter of wurtzite GaN (W-GaN). For ZB-GaN:Eu, a large fraction of Eu ions is found on a high symmetry interstitial site aligned with the <110> direction, while a Ga substitutional site is observed for W-GaN:Eu. The implantation damage in ZB-GaN:Eu could partly be removed by thermal annealing, but an increase in the wurtzite phase fraction was observed at the same time. Cathodoluminescence, photoluminescence (PL), and PL excitation spectroscopy revealed several emission lines which can be attributed to distinct Eu-related optical centers in ZB-GaN and W-GaN inclusions.

  7. ODENDOR of Defects in GaN Epitaxial Layers

    NASA Astrophysics Data System (ADS)

    Glaser, E. R.; Kennedy, T. A.; Carlos, W. E.; Freitas, J. A., Jr.; Wickenden, A. E.; Koleske, D. D.

    1998-03-01

    Optically-detected electron-nuclear double resonance (ODENDOR) at 24 GHz has been performed on a set of GaN epitaxial layers (undoped and Si-doped) grown on Al_2O3 to identify and locate residual defects and dopants.(E.R. Glaser et al., submitted to Phys. Rev. B) The first observation was made by the Paderborn group.(F.K. Koschnick et al., Phys. Rev. B 54, R11042 (1996).) Strong ODENDOR with resolved quadrupole structure was observed between 6 and 14 MHz on the g = 1.951 effective-mass (EM) donor resonance found on the 2.2 eV emission bands from two high-resistivity films (n <= 1x10^16 cm-3). The lines are assigned to ^69,71Ga lattice nuclei coupled to the residual donors through a weak hyperfine interaction (<= 1 MHz). The quadrupole splitting of ~ 2.3 MHz found for ^69Ga varies between samples and in comparison to published values for strain-free GaN by 15-25 %. The symmetry of the electric field gradient provides evidence that the donors are located in the crystallites rather than near grain boundaries. ODENDOR was not found between 1.5 and 140 MHz on the g = 1.991 deep defect resonances. Possible reasons for the absence of signals will be discussed.

  8. Atomic layer deposition of GaN at low temperatures

    SciTech Connect

    Ozgit, Cagla; Donmez, Inci; Alevli, Mustafa; Biyikli, Necmi

    2012-01-15

    The authors report on the self-limiting growth of GaN thin films at low temperatures. Films were deposited on Si substrates by plasma-enhanced atomic layer deposition using trimethylgallium (TMG) and ammonia (NH{sub 3}) as the group-III and -V precursors, respectively. GaN deposition rate saturated at 185 deg. C for NH{sub 3} doses starting from 90 s. Atomic layer deposition temperature window was observed from 185 to {approx}385 deg. C. Deposition rate, which is constant at {approx}0.51 A/cycle within the temperature range of 250 - 350 deg. C, increased slightly as the temperature decreased to 185 deg. C. In the bulk film, concentrations of Ga, N, and O were constant at {approx}36.6, {approx}43.9, and {approx}19.5 at. %, respectively. C was detected only at the surface and no C impurities were found in the bulk film. High oxygen concentration in films was attributed to the oxygen impurities present in group-V precursor. High-resolution transmission electron microscopy studies revealed a microstructure consisting of small crystallites dispersed in an amorphous matrix.

  9. A GaN photonic crystal membrane laser.

    PubMed

    Lin, Cheng-Hung; Wang, Jyh-Yang; Chen, Cheng-Yen; Shen, Kun-Ching; Yeh, Dong-Ming; Kiang, Yean-Woei; Yang, C C

    2011-01-14

    The implementation of a series of optically pumped GaN photonic crystal (PhC) membrane lasers is demonstrated at room temperature. The photonic crystal is composed of a scalene-triangular arrangement of circular holes in GaN. Three defect structures are fabricated for comparing their lasing characteristics with those of perfect PhC. It is observed that all the lasing defect modes have lasing wavelengths very close to the band-edge modes in the perfect PhC structure. Although those lasing modes, including band-edge and defect modes, have different optical pump thresholds, different lasing spectral widths, different quality factors (Q factors), and different polarization ratios, all their polarization distributions show maxima in the directions around one of the hole arrangement axes. The similar lasing characteristics between the band-edge and defect modes are attributed to the existence of extremely narrow partial band gaps for forming the defect modes. Also, the oriented polarization properties are due to the scalene-triangle PhC structure. In one of the defect lasing modes, the lasing threshold is as low as 0.82 mJ cm(-2), the cavity Q factor is as large as 1743, and the polarization ratio is as large as 25.4. Such output parameters represent generally superior lasing behaviors when compared with previously reported implementations of similar laser structures.

  10. Nearly stress-free substrates for GaN homoepitaxy

    NASA Astrophysics Data System (ADS)

    Hermann, M.; Gogova, D.; Siche, D.; Schmidbauer, M.; Monemar, B.; Stutzmann, M.; Eickhoff, M.

    2006-08-01

    High-quality 300 μm thick GaN crack-free layers grown by hydride vapor phase epitaxy (HVPE) on c-plane sapphire without buffer layers and separated from the substrate by laser lift-off were investigated by high resolution X-ray diffraction (XRD), low-temperature photoluminescence and cathodoluminescence. All these characterization techniques confirm the high structural quality of the resulting material. Lateral X-ray mapping of the free-standing bulk-like GaN shows a homogeneous compressive stress of less than 40 MPa and a heterogeneous stress of about 80 MPa. The formation of twin grains (domains) were observed both in the reciprocal space mapping of the (2 0 .5) reflection and in rocking curve measurements. The latter ones revealed an estimated lateral coherence length of about 1.2 μm. The crystallite size along the c-axis is estimated to be larger than 20 μm. An upper limit of the density of dislocations with a component of the Burgers vector along the c-axis (screw and mixed type) of 1.3×10 7 cm -2 was extracted from the XRD data, while transmission electron microscopy measurements revealed a dislocation density of 1.7×10 7 cm -2. Thus, these layers are suitable as lattice-parameter and thermal-expansion matched substrates for strain-free homoepitaxy of GaN-based device heterostructures.

  11. Excitation mechanisms of Er optical centers GaN epilayers

    NASA Astrophysics Data System (ADS)

    Hawkins, Matthew; Jiang, Hongxing; Lin, Jingyu; Zavada, John; Vinh, Nguyen

    We report direct evidence of two mechanisms responsible for the excitation of optically active Er3 + ions in GaN epilayers grown by metal-organic chemical vapor deposition. These mechanisms, resonant excitation via the higher-lying inner 4f shell transitions and band-to-band excitation of the semiconductor host, lead to narrow emission lines from isolated and the defect-related Er optical centers. However, these centers have different photoluminescence spectra, local defect environments, decay dynamics, and excitation cross sections. The photoluminescence at 1.54 micrometer from the isolated Er optical center which can be excited by either mechanism has the same decay dynamics, but possesses a much higher excitation cross-section under band-to-band excitation. In contrast, the photoluminescence at 1.54 micrometer from the defect-related Er optical center can only be observed through band-to-band excitation but has the largest excitation cross-section. These results explain the difficulty in achieving gain in Er doped GaN and indicate approaches for realization of optical amplification, and possibly lasing, at room temperature.

  12. Research on quantum efficiency of GaN wire photocathode

    NASA Astrophysics Data System (ADS)

    Xia, Sihao; Liu, Lei; Diao, Yu; Kong, Yike

    2017-02-01

    On the basis of three-dimensional continuity equation in semiconductors and finite difference method, the carrier concentration and the quantum efficiency of GaN wire photocathode as a function of incident photon energy are achieved. Results show that the quantum efficiency of the wire photocathode is largely enhanced compared with the conventional planar photocathode. The superiority of the wire photocathode is reflected in its structure with surrounding surfaces. The quantum efficiency of the wire photocathode largely depends on the wire width, surface reflectivity, surface escape probability and incident angle of light. The back interface recombination rate, however, has little influences on the quantum efficiency of the wire photocathode. The simulation results suggest that the optimal width for photoemission is 150-200 nm. Besides, the quantum efficiency increases and decreases linearly with increasing surface escape probability and surface reflectivity, respectively. With increasing ratio of wire spacing to wire height, the optimal incident angle of light is reduced. These simulations are expected to guide the preparation of a better performing GaN wire photocathode.

  13. An Electrophysiological Investigation of Early Effects of Masked Morphological Priming

    ERIC Educational Resources Information Center

    Morris, Joanna; Grainger, Jonathan; Holcomb, Phillip J.

    2008-01-01

    This experiment examined event-related responses to targets preceded by semantically transparent morphologically related primes (e.g., farmer-farm), semantically opaque primes with an apparent morphological relation (corner-corn), and orthographically, but not morphologically, related primes (scandal-scan) using the masked priming technique…

  14. Masked Priming from Orthographic Neighbors: An ERP Investigation

    ERIC Educational Resources Information Center

    Massol, Stephanie; Grainger, Jonathan; Dufau, Stephane; Holcomb, Phillip

    2010-01-01

    Two experiments combined masked priming with event-related potential (ERP) recordings to examine effects of primes that are orthographic neighbors of target words. Experiment 1 compared effects of repetition primes with effects of primes that were high-frequency orthographic neighbors of low-frequency targets (e.g., faute-faune [error-wildlife]),…

  15. Priming Ability-Relevant Social Categories Improves Intellectual Test Performance

    ERIC Educational Resources Information Center

    Lin, Phoebe S.; Kennette, Lynne N.; Van Havermaet, Lisa R.; Frank, Nichole M.; McIntyre, Rusty B.

    2012-01-01

    Research shows that priming affects behavioral tasks; fewer studies, however, have been conducted on how social category primes affect cognitive tasks. The present study aimed to examine the effects of social category primes on math performance and word recall. It was hypothesized that Asian prime words would improve math performance and word…

  16. Semantic Priming for Coordinate Distant Concepts in Alzheimer's Disease Patients

    ERIC Educational Resources Information Center

    Perri, R.; Zannino, G. D.; Caltagirone, C.; Carlesimo, G. A.

    2011-01-01

    Semantic priming paradigms have been used to investigate semantic knowledge in patients with Alzheimer's disease (AD). While priming effects produced by prime-target pairs with associative relatedness reflect processes at both lexical and semantic levels, priming effects produced by words that are semantically related but not associated should…

  17. Processing Speaker Variability in Repetition and Semantic/Associative Priming

    ERIC Educational Resources Information Center

    Lee, Chao-Yang; Zhang, Yu

    2015-01-01

    The effect of speaker variability on accessing the form and meaning of spoken words was evaluated in two short-term priming experiments. In the repetition priming experiment, participants listened to repeated or unrelated prime-target pairs, in which the prime and target were produced by the same speaker or different speakers. The results showed…

  18. Cytokinin primes plant responses to wounding and reduces insect performance

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We report a potential role of endogenous cytokinin supply in priming plant defense against herbivory. Cytokinin priming significantly reduced weight gain by insect larvae. Unlike previously described priming by volatile compounds, priming by cytokinin did not overcome vascular restrictions on system...

  19. Masked Inhibitory Priming in English: Evidence for Lexical Inhibition

    ERIC Educational Resources Information Center

    Davis, Colin J.; Lupker, Stephen J.

    2006-01-01

    Predictions derived from the interactive activation (IA) model were tested in 3 experiments using the masked priming technique in the lexical decision task. Experiment 1 showed a strong effect of prime lexicality: Classifications of target words were facilitated by orthographically related nonword primes (relative to unrelated nonword primes) but…

  20. Pure Mediated Priming: A Retrospective Semantic Matching Model

    ERIC Educational Resources Information Center

    Jones, Lara L.

    2010-01-01

    Mediated priming refers to the activation of a target (e.g., "stripes") by a prime (e.g., "lion") that is related indirectly via a connecting mediator (e.g., tiger). In previous mediated priming studies (e.g., McNamara & Altarriba, 1988), the mediator was associatively related to the prime. In contrast, pure mediated…

  1. Decomposition of Repetition Priming Components in Picture Naming

    ERIC Educational Resources Information Center

    Francis, Wendy S.; Corral, Nuvia I.; Jones, Mary L.; Saenz, Silvia P.

    2008-01-01

    Cognitive mechanisms underlying repetition priming in picture naming were decomposed in several experiments. Sets of encoding manipulations meant to selectively prime or reduce priming in object identification or word production components of picture naming were combined factorially to dissociate processes underlying priming in picture naming.…

  2. 46 CFR 111.12-1 - Prime movers.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... REQUIREMENTS Generator Construction and Circuits § 111.12-1 Prime movers. (a) Prime movers must meet section 58...-1). Further requirements for emergency generator prime movers are in 46 CFR subpart 112.50. (b) Each generator prime mover must have an overspeed device that is independent of the normal operating governor...

  3. 46 CFR 111.12-1 - Prime movers.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... REQUIREMENTS Generator Construction and Circuits § 111.12-1 Prime movers. (a) Prime movers must meet section 58...-1). Further requirements for emergency generator prime movers are in 46 CFR subpart 112.50. (b) Each generator prime mover must have an overspeed device that is independent of the normal operating governor...

  4. 46 CFR 111.12-1 - Prime movers.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... REQUIREMENTS Generator Construction and Circuits § 111.12-1 Prime movers. (a) Prime movers must meet section 58...-1). Further requirements for emergency generator prime movers are in 46 CFR subpart 112.50. (b) Each generator prime mover must have an overspeed device that is independent of the normal operating governor...

  5. 46 CFR 111.12-1 - Prime movers.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... REQUIREMENTS Generator Construction and Circuits § 111.12-1 Prime movers. (a) Prime movers must meet section 58...-1). Further requirements for emergency generator prime movers are in 46 CFR subpart 112.50. (b) Each generator prime mover must have an overspeed device that is independent of the normal operating governor...

  6. 46 CFR 111.12-1 - Prime movers.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... REQUIREMENTS Generator Construction and Circuits § 111.12-1 Prime movers. (a) Prime movers must meet section 58...-1). Further requirements for emergency generator prime movers are in 46 CFR subpart 112.50. (b) Each generator prime mover must have an overspeed device that is independent of the normal operating governor...

  7. Quantitative two-dimensional EXSY spectroscopy and dynamic behavior of a paramagnetic lanthanide macrocyclic chelate: YbDOTA (DOTA = 1,4,7,10-tetraazacyclododecane-N,N{prime},N{double_prime},N{double_prime}{prime}-tetraacetic acid)

    SciTech Connect

    Jacques, V.; Desreux, J.F.

    1994-08-31

    The chelate, YbDOTA (DOTA = 1,4,7,10-tetraazacyclododecane-N,N{prime},N{double_prime},N{double_prime}{prime}-tetraacetic acid) has two possible conformations. Interconversion between isomers was studied by EXSY NMR spectroscopy. The activation energy for conversion was found to be 65.6 kJ/mol for conversion from the major to the minor species.

  8. Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

    SciTech Connect

    Kushvaha, S. S.; Kumar, M. Senthil; Maurya, K. K.; Dalai, M. K.; Sharma, Nita D.

    2013-09-15

    Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

  9. Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

    NASA Astrophysics Data System (ADS)

    Kushvaha, S. S.; Kumar, M. Senthil; Maurya, K. K.; Dalai, M. K.; Sharma, Nita D.

    2013-09-01

    Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500-750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

  10. Size dependence of melting of GaN nanowires with triangular cross sections

    SciTech Connect

    Wang, Zhiguo; Zu, Xiaotao; Gao, Fei; Weber, William J.

    2007-02-15

    Molecular dynamics simulations have been used to study the melting of GaN nanowires with triangular cross-sections. The curve of the potential energy, along with the atomic configuration is used to monitor the phase transition. The thermal stability of GaN nanowires is dependent on the size of the nanowires. The melting temperature of the GaN nanowires increases with the increasing of area cross-section of the nanowires to a saturation value. An interesting result is that of the nanowires start to melt from the edges, then the surface, and extends to the inner regions of nanowires as temperature increases.

  11. Interfacial Structure and Chemistry of GaN on Ge(111)

    NASA Astrophysics Data System (ADS)

    Zhang, Siyuan; Zhang, Yucheng; Cui, Ying; Freysoldt, Christoph; Neugebauer, Jörg; Lieten, Ruben R.; Barnard, Jonathan S.; Humphreys, Colin J.

    2013-12-01

    The interface of GaN grown on Ge(111) by plasma-assisted molecular beam epitaxy is resolved by aberration corrected scanning transmission electron microscopy. A novel interfacial structure with a 5∶4 closely spaced atomic bilayer is observed that explains why the interface is flat, crystalline, and free of GeNx. Density functional theory based total energy calculations show that the interface bilayer contains Ge and Ga atoms, with no N atoms. The 5∶4 bilayer at the interface has a lower energy than a direct stacking of GaN on Ge(111) and enables the 5∶4 lattice-matching growth of GaN.

  12. Stress and Defect Control in GaN Using Low Temperature Interlayers

    SciTech Connect

    Akasaki, I.; Amano, H.; Chason, E.; Figiel, J.; Floro, J.A.; Han, J.; Hearne, S.; Iwaya, M.; Kashima, T.; Katsuragcawa, M.

    1998-12-04

    In organometallic vapor phase epitaxial growth of Gail on sapphire, the role of the low- temperature-deposited interlayers inserted between high-temperature-grown GaN layers was investigated by in situ stress measurement, X-ray diffraction, and transmission electron microscopy. Insertion of a series of low temperature GaN interlayers reduces the density of threading dislocations while simultaneously increasing the tensile stress during growth, ultimately resulting in cracking of the GaN film. Low temperature AIN interlayers were found to be effective in suppressing cracking by reducing tensile stress. The intedayer approach permits tailoring of the film stress to optimize film structure and properties.

  13. Etching of GaN layers at electrolysis under UV-irradiation

    NASA Astrophysics Data System (ADS)

    Zubenko, T. K.; Puzyk, M. V.; Stozharov, V. M.; Ermakov, I. A.; Kovalev, D. S.; Ivanova, S. A.; Usikov, A. S.; Medvedev, O. S.; Papchenko, B. P.; Kurin, S. Yu; Antipov, A. A.; Chernyakov, A. E.

    2016-08-01

    Etching of the GaN layers in 1M KOH aqua solution under irradiation was studied by the electro-stimulated photolysis using N2-laser (337 nm, 60 W/m2) as a light source. It was observed that the size and the depth of the failure monotonically depend on the optical power and the irradiation time of the N2 laser and the GaN layer type of conductivity. The GaN layers etching rate was evaluated. A mechanism of the failure in the n-GaN layers is discussed.

  14. Modulation of 2{prime}-5{prime} oligoadenylate synthetase by environmental stress in the marine sponge Geodia cydonium

    SciTech Connect

    Schroeder, H.C.; Wiens, M.; Mueller, W.E.G.; Kuusksalu, A.; Kelve, M.

    1997-07-01

    Recently the authors established the presence of relatively high amounts of 2{prime}-5{prime} oligoadenylates (2{prime}-5{prime} A) and 2{prime}-5{prime} oligoadenylate synthetase (2{prime}-5{prime} A synthetase) in the marine sponge Geodia cydonium. Here they determined by applying radioimmunoassay and high-performance liquid chromatographical methods that the concentration of 2{prime}-5{prime} A synthetase change following exposure of G. cydonium tissue to environmental stress. The 2{prime}-5{prime} A content and the activity of 2{prime}-5{prime} A synthetase, present in crude sponge extract, increase by up to three-fold after treating sponge cubes for 2 h with natural stressors including heat shock (26 C), cold shock (6 C), pH shock (pH 6), and hypertonic shock and subsequent incubation for 18 h under ambient conditions (16 C). No response was observed after exposure of sponges to an alkaline (pH 10) or hypotonic environment. Similar changes have been found for the expression of heat shock protein HSP70 in G. cydonium. These results show that 2{prime}-5{prime} A in sponges may be useful as a novel biomarker for environmental monitoring.

  15. An ERP Investigation of Masked Cross-Script Translation Priming

    PubMed Central

    Hoshino, Noriko; Midgley, Katherine J.; Holcomb, Phillip J.; Grainger, Jonathan

    2010-01-01

    The time course of cross-script translation priming and repetition priming was examined in two different scripts using a combination of the masked priming paradigm with the recording of event-related potentials (ERPs). Japanese-English bilinguals performed a semantic categorization task in their second language (L2) English and in their first language (L1) Japanese. Targets were preceded by a visually presented related (translation equivalent/repeated) or unrelated prime. The results showed that the amplitudes of the N250 and N400 ERP components were significantly modulated for L2-L2 repetition priming, L1-L2 translation priming, and L1-L1 repetition priming, but not for L2-L1 translation priming. There was also evidence for priming effects in an earlier 100-200 ms time window for L1-L1 repetition priming and L1-L2 translation priming. We argue that a change in script across primes and targets provides optimal conditions for prime word processing, hence generating very fast-acting translation priming effects when primes are in L1. PMID:20478274

  16. [Priming effects in picture problems: preliminary solutions].

    PubMed

    Wippich, W; Mecklenbräuker, S; Weidmann, K; Reichert, A

    1995-01-01

    Two experiments explored whether picture puzzles are an adequate instrument to investigate implicit memory for pictorial information. During the testing phase, the subjects had to identify hidden figures in picture puzzles. In a preceding learning phase, the priming conditions were varied systematically. In the first experiment, some subjects had to solve picture puzzles in the learning phase, whereas others made esthetic judgments (global processing) or estimated the number of triangles in the picture puzzles (local processing). In the second experiment, the subjects inspected copies of figures that were hidden at testing, modified versions of these figures, or their names in the learning phase. In the first experiment, the subjects of the different encoding conditions showed comparable priming effects. Picture puzzles that had already been processed or seen during learning were solved more often than new ones. Interview data revealed that subjects in the local or global processing conditions did not identify hidden figures at encoding. Furthermore, these subjects could not discriminate between old and new picture puzzles in a final explicit test of recognition. Thus, nonconscious storage of perceptual information that is not semantically interpreted may be sufficient to evoke priming effects. In the second experiment, the subjects in the different encoding conditions showed reliable priming effects, too. The presentation of the duplicates at encoding produced the greatest amount of priming. Effects of verbal priming, however, indicate that the solution of picture puzzles is not based solely on perceptual information. Depending on the priming conditions at learning, the solution of picture puzzles may be based primarily on data-driven processing or may be guided more heavily by conceptual information. It is concluded that perceptual, lexical, and/or conceptual information can contribute to the solution of picture puzzles.

  17. Implicit phonological priming during visual word recognition.

    PubMed

    Wilson, Lisa B; Tregellas, Jason R; Slason, Erin; Pasko, Bryce E; Rojas, Donald C

    2011-03-15

    Phonology is a lower-level structural aspect of language involving the sounds of a language and their organization in that language. Numerous behavioral studies utilizing priming, which refers to an increased sensitivity to a stimulus following prior experience with that or a related stimulus, have provided evidence for the role of phonology in visual word recognition. However, most language studies utilizing priming in conjunction with functional magnetic resonance imaging (fMRI) have focused on lexical-semantic aspects of language processing. The aim of the present study was to investigate the neurobiological substrates of the automatic, implicit stages of phonological processing. While undergoing fMRI, eighteen individuals performed a lexical decision task (LDT) on prime-target pairs including word-word homophone and pseudoword-word pseudohomophone pairs with a prime presentation below perceptual threshold. Whole-brain analyses revealed several cortical regions exhibiting hemodynamic response suppression due to phonological priming including bilateral superior temporal gyri (STG), middle temporal gyri (MTG), and angular gyri (AG) with additional region of interest (ROI) analyses revealing response suppression in the left lateralized supramarginal gyrus (SMG). Homophone and pseudohomophone priming also resulted in different patterns of hemodynamic responses relative to one another. These results suggest that phonological processing plays a key role in visual word recognition. Furthermore, enhanced hemodynamic responses for unrelated stimuli relative to primed stimuli were observed in midline cortical regions corresponding to the default-mode network (DMN) suggesting that DMN activity can be modulated by task requirements within the context of an implicit task.

  18. Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs

    PubMed Central

    Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

    2015-01-01

    High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This “compliant” buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 105 cm−2. In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6” wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors. PMID:26329829

  19. Early Morphological Decomposition of Suffixed Words: Masked Priming Evidence with Transposed-Letter Nonword Primes

    ERIC Educational Resources Information Center

    Beyersmann, Elisabeth; Dunabeitia, Jon Andoni; Carreiras, Manuel; Coltheart, Max; Castles, Anne

    2013-01-01

    Many studies have previously reported that the recognition of a stem target (e.g., "teach") is facilitated by the prior masked presentation of a prime consisting of a derived form of it (e.g., "teacher"). We conducted two lexical decision experiments to investigate masked morphological priming in Spanish. Experiment 1 showed…

  20. Smelly primes – when olfactory primes do or do not work

    PubMed Central

    Smeets, M. A. M.; Dijksterhuis, G. B.

    2014-01-01

    In applied olfactory cognition the effects that olfactory stimulation can have on (human) behavior are investigated. To enable an efficient application of olfactory stimuli a model of how they may lead to a change in behavior is proposed. To this end we use the concept of olfactory priming. Olfactory priming may prompt a special view on priming as the olfactory sense has some unique properties which make odors special types of primes. Examples of such properties are the ability of odors to influence our behavior outside of awareness, to lead to strong affective evaluations, to evoke specific memories, and to associate easily and quickly to other environmental stimuli. Opportunities and limitations for using odors as primes are related to these properties, and alternative explanations for reported findings are offered. Implications for olfactory semantic, construal, behavior and goal priming are given based on a brief overview of the priming literature from social psychology and from olfactory perception science. We end by formulating recommendations and ideas for a future research agenda and applications for olfactory priming. PMID:24575071

  1. Priming tool actions: Are real objects more effective primes than pictures?

    PubMed

    Squires, Scott D; Macdonald, Scott N; Culham, Jody C; Snow, Jacqueline C

    2016-04-01

    Humans are faster to grasp an object such as a tool if they have previewed the same object beforehand. This priming effect is strongest when actors gesture the use of the tool rather than simply move it, possibly because the previewed tool activates action-specific routines in dorsal-stream motor networks. Here, we examined whether real tools, which observers could physically act upon, serve as more potent primes than two-dimensional images of tools, which do not afford physical action. Participants were presented with a prime stimulus that could be either a real tool or a visually matched photograph of a tool. After a brief delay, participants interacted with a real tool target, either by 'grasping to move,' or 'grasping to use' it. The identities of the prime and target tools were either the same (congruent trials; e.g., spatula-spatula) or different (incongruent trials; e.g., whisk-spatula). As expected, participants were faster to initiate grasps during trials when they had to move the tool rather than gesture its use. Priming effects were observed for grasp-to-use, but not grasp-to-move, responses. Surprisingly, however, both pictures of tools and real tools primed action responses equally. Our results indicate that tool priming effects are driven by pictorial cues and their implied actions, even in the absence of volumetric cues that reflect the tangibility and affordances of the prime.

  2. High breakdown single-crystal GaN p-n diodes by molecular beam epitaxy

    SciTech Connect

    Qi, Meng; Zhao, Yuning; Yan, Xiaodong; Li, Guowang; Verma, Jai; Fay, Patrick; Nomoto, Kazuki; Zhu, Mingda; Hu, Zongyang; Protasenko, Vladimir; Song, Bo; Xing, Huili Grace; Jena, Debdeep; Bader, Samuel

    2015-12-07

    Molecular beam epitaxy grown GaN p-n vertical diodes are demonstrated on single-crystal GaN substrates. A low leakage current <3 nA/cm{sup 2} is obtained with reverse bias voltage up to −20 V. With a 400 nm thick n-drift region, an on-resistance of 0.23 mΩ cm{sup 2} is achieved, with a breakdown voltage corresponding to a peak electric field of ∼3.1 MV/cm in GaN. Single-crystal GaN substrates with very low dislocation densities enable the low leakage current and the high breakdown field in the diodes, showing significant potential for MBE growth to attain near-intrinsic performance when the density of dislocations is low.

  3. Controlled morphology of regular GaN microrod arrays by selective area growth with HVPE

    NASA Astrophysics Data System (ADS)

    Lekhal, Kaddour; Bae, Si-Young; Lee, Ho-Jun; Mitsunari, Tadashi; Tamura, Akira; Deki, Manato; Honda, Yoshio; Amano, Hiroshi

    2016-08-01

    The selective area growth (SAG) of GaN was implemented on patterned GaN/sapphire templates by hydride vapor phase epitaxy (HVPE) to fabricate regular arrays of Ga-polar GaN microrods. The control of growth parameters such as H2/N2 carrier gas ratio, growth temperature, and absolute NH3/HCl gas flow resulted in changes in the growth morphology. In particular, for an optimized mixed-carrier gas ratio of H2 to N2, we achieved vertically well-aligned microrods. The topmost regions of the GaN microrods were terminated with pyramidal facets, indicating typical Ga polarity. The optical properties of the grown microrods were characterized by cathodoluminescence (CL) at a low temperature. This revealed that the GaN microrods had high crystal quality since they exhibited suppressed yellow luminescence as well as strong band edge emission.

  4. Effects of Al additives on growth of GaN polycrystals by the Na flux method

    NASA Astrophysics Data System (ADS)

    Imabayashi, Hiroki; Murakami, Kosuke; Matsuo, Daisuke; Honjo, Masatomo; Imanishi, Masayuki; Maruyama, Mihoko; Imade, Mamoru; Yoshimura, Masashi; Mori, Yusuke

    2017-03-01

    In this study, we investigated the growth of GaN polycrystals using the Al-added Na flux method. We studied the effects of Al on accelerating the nucleation and purity of GaN polycrystals. The yields of GaN crystals grown in Al-added Na flux were dramatically increased from those in Al-free Na flux, and the polycrystals grown by the Al-added Na flux method were highly transparent. As observed in secondary ion mass spectroscopy measurements, the Al content of the polycrystals was below the detection limit of 3 × 1016 atoms/cm3. From these results, the Al-added Na flux method is found to be appropriate for fabricating a large amount of GaN polycrystals without deteriorating the crystal quality.

  5. Thermal Conductivity and Large Isotope Effect in GaN from First Principles

    SciTech Connect

    Lindsay, L.; Broido, D. A.; Reinecke, T. L.

    2012-08-28

    We present atomistic first principles results for the lattice thermal conductivity of GaN and compare them to those for GaP, GaAs, and GaSb. In GaN we find a large increase to the thermal conductivity with isotopic enrichment, ~65% at room temperature. We show that both the high thermal conductivity and its enhancement with isotopic enrichment in GaN arise from the weak coupling of heat-carrying acoustic phonons with optic phonons. This weak scattering results from stiff atomic bonds and the large Ga to N mass ratio, which give phonons high frequencies and also a pronounced energy gap between acoustic and optic phonons compared to other materials. Rigorous understanding of these features in GaN gives important insights into the interplay between intrinsic phonon-phonon scattering and isotopic scattering in a range of materials.

  6. Depth dependence of defect density and stress in GaN grown on SiC

    SciTech Connect

    Faleev, N.; Temkin, H.; Ahmad, I.; Holtz, M.; Melnik, Yu.

    2005-12-15

    We report high resolution x-ray diffraction studies of the relaxation of elastic strain in GaN grown on SiC(0001). The GaN layers were grown with thickness ranging from 0.29 to 30 {mu}m. High level of residual elastic strain was found in thin (0.29 to 0.73 {mu}m thick) GaN layers. This correlates with low density of threading screw dislocations of 1-2x10{sup 7} cm{sup -2}, observed in a surface layer formed over a defective nucleation layer. Stress was found to be very close to what is expected from thermal expansion mismatch between the GaN and SiC. A model based on generation and diffusion of point defects accounts for these observations.

  7. Radiative defects in GaN nanocolumns: Correlation with growth conditions and sample morphology

    SciTech Connect

    Lefebvre, P.; Fernandez-Garrido, S.; Grandal, J.; Ristic, J.; Sanchez-Garcia, M.-A.; Calleja, E.

    2011-02-21

    Low-temperature photoluminescence is studied in detail in GaN nanocolumns (NCs) grown by plasma-assisted molecular beam epitaxy under various conditions (substrate temperature and impinging Ga/N flux ratio). The relative intensities of the different emission lines, in particular those related to structural defects, appear to be correlated with the growth conditions, and clearly linked to the NC sample morphology. We demonstrate, in particular, that all lines comprised between 3.10 and 3.42 eV rapidly lose intensity when the growth conditions are such that the NC coalescence is reduced. The well-known line around 3.45 eV, characteristic of GaN NC samples, shows, however, a behavior that is exactly the opposite of the other lines, namely, for growth conditions leading to reduced NC coalescence, this line tends to become more prominent, thus proving to be intrinsic to individual GaN NCs.

  8. Formation of helical dislocations in ammonothermal GaN substrate by heat treatment

    NASA Astrophysics Data System (ADS)

    Horibuchi, Kayo; Yamaguchi, Satoshi; Kimoto, Yasuji; Nishikawa, Koichi; Kachi, Tetsu

    2016-03-01

    GaN substrate produced by the basic ammonothermal method and an epitaxial layer on the substrate was evaluated using synchrotron radiation x-ray topography and transmission electron microscopy. We revealed that the threading dislocations present in the GaN substrate are deformed into helical dislocations and the generation of the voids by heat treatment in the substrate for the first observation in the GaN crystal. These phenomena are formed by the interactions between the dislocations and vacancies. The helical dislocation was formed in the substrate region, and not in the epitaxial layer region. Furthermore, the evaluation of the influence of the dislocations on the leakage current of Schottky barrier diodes fabricated on the epitaxial layer is discussed. The dislocations did not affect the leakage current characteristics of the epitaxial layer. Our results suggest that the deformation of dislocations in the GaN substrate does not adversely affect the epitaxial layer.

  9. Surface potential barrier in m-plane GaN studied by contactless electroreflectance

    NASA Astrophysics Data System (ADS)

    Janicki, Lukasz; Misiewicz, Jan; Cywiński, Grzegorz; Sawicka, Marta; Skierbiszewski, Czeslaw; Kudrawiec, Robert

    2016-02-01

    Contactless electroreflectance (CER) is used to study the surface potential barrier in m-plane GaN UN+ [GaN (d = 20,30,50,70 nm)/GaN:Si] structures grown by using molecular beam epitaxy. Clear bandgap-related transitions followed by Franz-Keldysh oscillations (FKO) have been observed in the CER spectra of all samples at room temperature. The built-in electric fields in the undoped cap layers have been determined from the FKO period. From the built-in electric field and the undoped GaN layer thickness, the Fermi level location at the air-exposed m-plane GaN surface has been estimated as 0.42 ± 0.05 eV below the conduction band.

  10. Thermal conductivity and large isotope effect in GaN from first principles.

    PubMed

    Lindsay, L; Broido, D A; Reinecke, T L

    2012-08-31

    We present atomistic first principles results for the lattice thermal conductivity of GaN and compare them to those for GaP, GaAs, and GaSb. In GaN we find a large increase to the thermal conductivity with isotopic enrichment, ~65% at room temperature. We show that both the high thermal conductivity and its enhancement with isotopic enrichment in GaN arise from the weak coupling of heat-carrying acoustic phonons with optic phonons. This weak scattering results from stiff atomic bonds and the large Ga to N mass ratio, which give phonons high frequencies and also a pronounced energy gap between acoustic and optic phonons compared to other materials. Rigorous understanding of these features in GaN gives important insights into the interplay between intrinsic phonon-phonon scattering and isotopic scattering in a range of materials.

  11. Boron doped GaN and InN: Potential candidates for spintronics

    NASA Astrophysics Data System (ADS)

    Fan, S. W.; Huang, X. N.; Yao, K. L.

    2017-02-01

    The full potential linearized augmented plane wave method together with the Tran-Blaha modified Becke-Johnson potential is utilized to investigate the electronic structures and magnetism for boron doped GaN and InN. Calculations show the boron substituting nitrogen (BN defects) could induce the GaN and InN to be half-metallic ferromagnets. The magnetic moments mainly come from the BN defects, and each BN defect would produce the 2.00 μB total magnetic moment. The electronic structures indicate the carriers-mediated double exchange interaction plays a crucial role in forming the ferromagnetism. Positive chemical pair interactions imply the BN defects would form the homogeneous distribution in GaN and InN matrix. Moderate formation energies suggest that GaN and InN with BN defects could be fabricated experimentally.

  12. Above room-temperature ferromagnetism of Mn delta-doped GaN nanorods

    SciTech Connect

    Lin, Y. T.; Wadekar, P. V.; Kao, H. S.; Chen, T. H.; Chen, Q. Y.; Tu, L. W.; Huang, H. C.; Ho, N. J.

    2014-02-10

    One-dimensional nitride based diluted magnetic semiconductors were grown by plasma-assisted molecular beam epitaxy. Delta-doping technique was adopted to dope GaN nanorods with Mn. The structural and magnetic properties were investigated. The GaMnN nanorods with a single crystalline structure and with Ga sites substituted by Mn atoms were verified by high-resolution x-ray diffraction and Raman scattering, respectively. Secondary phases were not observed by high-resolution x-ray diffraction and high-resolution transmission electron microscopy. In addition, the magnetic hysteresis curves show that the Mn delta-doped GaN nanorods are ferromagnetic above room temperature. The magnetization with magnetic field perpendicular to GaN c-axis saturates easier than the one with field parallel to GaN c-axis.

  13. High-resistance GaN epilayers with low dislocation density via growth mode modification

    NASA Astrophysics Data System (ADS)

    Xu, Z. Y.; Xu, F. J.; Wang, J. M.; Lu, L.; Yang, Z. J.; Wang, X. Q.; Shen, B.

    2016-09-01

    High-resistance GaN with low dislocation density adopting growth mode modification has been investigated by metalorganic chemical vapor deposition. The sheet resistance of the order of 1016 Ω/sq has been achieved at room temperature by diminishing the oxygen impurity level close to the substrate with an AlN blocking layer. Attributed to this method which offers more freedom to tailor the growth mode, a three-dimensional (3D) growth process is introduced by adjusting the growth pressure and temperature at the initial stage of the GaN epitaxy to improve the crystalline quality. The large 3D GaN grains formed during this period roughen the surface, and the following coalescence of the GaN grains causes threading dislocations bending, which finally remarkably reduces the dislocation density.

  14. Lexical–semantic priming effects during infancy

    PubMed Central

    Arias-Trejo, Natalia; Plunkett, Kim

    2009-01-01

    When and how do infants develop a semantic system of words that are related to each other? We investigated word–word associations in early lexical development using an adaptation of the inter-modal preferential looking task where word pairs (as opposed to single target words) were used to direct infants’ attention towards a target picture. Two words (prime and target) were presented in quick succession after which infants were presented with a picture pair (target and distracter). Prime–target word pairs were either semantically and associatively related or unrelated; the targets were either named or unnamed. Experiment 1 demonstrated a lexical–semantic priming effect for 21-month olds but not for 18-month olds: unrelated prime words interfered with linguistic target identification for 21-month olds. Follow-up experiments confirmed the interfering effects of unrelated prime words and identified the existence of repetition priming effects as young as 18 months of age. The results of these experiments indicate that infants have begun to develop semantic–associative links between lexical items as early as 21 months of age. PMID:19933137

  15. Avoid self-priming centrifugal pump

    SciTech Connect

    Reeves, G.G.

    1987-01-01

    The self-priming horizontal centrifugal pump becomes known to its operator either as a good pump or a bad pump. The latter is usually replaced by another type of pump, even though a properly specified self-priming centrifugal pump might have been a good choice. Use of the guidelines described in this article are intended to help in the purchase and installation of a good pump. Self-priming centrifugal pumps are used for removing liquids from below grade sumps or pits that may also contain solids, fibers and/or muck. Alternate pumps for this service include submersible pumps, vertical turbine pumps and positive displacement pumps. These alternate pumps do not pass solid particles as large as self-priming pumps do without damage. Positive displacement pumps are not normally cost-effective when pumping liquid at rates in excess of 500 gallons per minute in low-head applications. Vertical and submersible pumps must be removed when cleaning of the pump is required. Self-priming pumps are easily cleaned by opening the access plates without moving the pump; and they cost less than the other types.

  16. A computational approach to negative priming

    NASA Astrophysics Data System (ADS)

    Schrobsdorff, H.; Ihrke, M.; Kabisch, B.; Behrendt, J.; Hasselhorn, M.; Herrmann, J. Michael

    2007-09-01

    Priming is characterized by a sensitivity of reaction times to the sequence of stimuli in psychophysical experiments. The reduction of the reaction time observed in positive priming is well-known and experimentally understood (Scarborough et al., J. Exp. Psycholol: Hum. Percept. Perform., 3, pp. 1-17, 1977). Negative priming—the opposite effect—is experimentally less tangible (Fox, Psychonom. Bull. Rev., 2, pp. 145-173, 1995). The dependence on subtle parameter changes (such as response-stimulus interval) usually varies. The sensitivity of the negative priming effect bears great potential for applications in research in fields such as memory, selective attention, and ageing effects. We develop and analyse a computational realization, CISAM, of a recent psychological model for action decision making, the ISAM (Kabisch, PhD thesis, Friedrich-Schiller-Universitat, 2003), which is sensitive to priming conditions. With the dynamical systems approach of the CISAM, we show that a single adaptive threshold mechanism is sufficient to explain both positive and negative priming effects. This is achieved by comparing results obtained by the computational modelling with experimental data from our laboratory. The implementation provides a rich base from which testable predictions can be derived, e.g. with respect to hitherto untested stimulus combinations (e.g. single-object trials).

  17. Priming Intelligent Behavior: An Elusive Phenomenon

    PubMed Central

    Shanks, David R.; Newell, Ben R.; Lee, Eun Hee; Balakrishnan, Divya; Ekelund, Lisa; Cenac, Zarus; Kavvadia, Fragkiski; Moore, Christopher

    2013-01-01

    Can behavior be unconsciously primed via the activation of attitudes, stereotypes, or other concepts? A number of studies have suggested that such priming effects can occur, and a prominent illustration is the claim that individuals' accuracy in answering general knowledge questions can be influenced by activating intelligence-related concepts such as professor or soccer hooligan. In 9 experiments with 475 participants we employed the procedures used in these studies, as well as a number of variants of those procedures, in an attempt to obtain this intelligence priming effect. None of the experiments obtained the effect, although financial incentives did boost performance. A Bayesian analysis reveals considerable evidential support for the null hypothesis. The results conform to the pattern typically obtained in word priming experiments in which priming is very narrow in its generalization and unconscious (subliminal) influences, if they occur at all, are extremely short-lived. We encourage others to explore the circumstances in which this phenomenon might be obtained. PMID:23637732

  18. Priming for novel object associations: Neural differences from object item priming and equivalent forms of recognition.

    PubMed

    Gomes, Carlos Alexandre; Figueiredo, Patrícia; Mayes, Andrew

    2016-04-01

    The neural substrates of associative and item priming and recognition were investigated in a functional magnetic resonance imaging study over two separate sessions. In the priming session, participants decided which object of a pair was bigger during both study and test phases. In the recognition session, participants saw different object pairs and performed the same size-judgement task followed by an associative recognition memory task. Associative priming was accompanied by reduced activity in the right middle occipital gyrus as well as in bilateral hippocampus. Object item priming was accompanied by reduced activity in extensive priming-related areas in the bilateral occipitotemporofrontal cortex, as well as in the perirhinal cortex, but not in the hippocampus. Associative recognition was characterized by activity increases in regions linked to recollection, such as the hippocampus, posterior cingulate cortex, anterior medial frontal gyrus and posterior parahippocampal cortex. Item object priming and recognition recruited broadly overlapping regions (e.g., bilateral middle occipital and prefrontal cortices, left fusiform gyrus), even though the BOLD response was in opposite directions. These regions along with the precuneus, where both item priming and recognition were accompanied by activation, have been found to respond to object familiarity. The minimal structural overlap between object associative priming and recollection-based associative recognition suggests that they depend on largely different stimulus-related information and that the different directions of the effects indicate distinct retrieval mechanisms. In contrast, item priming and familiarity-based recognition seemed mainly based on common memory information, although the extent of common processing between priming and familiarity remains unclear. Further implications of these findings are discussed.

  19. Modeling and Simulation of a Gallium Nitride (GaN) Betavoltaic Energy Converter

    DTIC Science & Technology

    2016-06-01

    ARL-TR-7675 ● JUNE 2016 US Army Research Laboratory Modeling and Simulation of a Gallium Nitride (GaN) Betavoltaic Energy ...Laboratory Modeling and Simulation of a Gallium Nitride (GaN) Betavoltaic Energy Converter by Marc S Litz and Johnny A Russo Sensors and Electron...GaN) Betavoltaic Energy Converter 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) William B Ray II, Marc S

  20. Linearity and Efficiency Performance of GaN HEMTs with Digital Pre-Distortion Correction (Preprint)

    DTIC Science & Technology

    2006-07-01

    AFRL-ML-WP-TP-2007-414 LINEARITY AND EFFICIENCY PERFORMANCE OF GaN HEMTs WITH DIGITAL PRE-DISTORTION CORRECTION (PREPRINT) M.J. Poulton, W.K...EFFICIENCY PERFORMANCE OF GaN HEMTs WITH DIGITAL PRE-DISTORTION CORRECTION (PREPRINT) 5c. PROGRAM ELEMENT NUMBER 62102F 5d. PROJECT NUMBER 4348...device performance using Digital Pre-Distortion (DPD) correction. Additionally, both drain voltage and current were optimized to provide high

  1. 10kW TWT Transition to GaN IRE

    DTIC Science & Technology

    2015-03-31

    replacement for the TWT. Phase I covered by this IRE, was to do market research on commercially available GaN transistors as a substitute for traveling wave...Phase I covered by this IRE, was to do market research on commercially available GaN transistors as a substitute for traveling wave tubes in high... Market Research Findings ........................................................................................ 8 3.1.2. Design Approach

  2. Strain dependent electron spin dynamics in bulk cubic GaN

    SciTech Connect

    Schaefer, A.; Buß, J. H.; Hägele, D.; Rudolph, J.; Schupp, T.; Zado, A.; As, D. J.

    2015-03-07

    The electron spin dynamics under variable uniaxial strain is investigated in bulk cubic GaN by time-resolved magneto-optical Kerr-rotation spectroscopy. Spin relaxation is found to be approximately independent of the applied strain, in complete agreement with estimates for Dyakonov-Perel spin relaxation. Our findings clearly exclude strain-induced relaxation as an effective mechanism for spin relaxation in cubic GaN.

  3. GaN Stress Evolution During Metal-Organic Chemical Vapor Deposition

    SciTech Connect

    Amano, H.; Chason, E.; Figiel, J.; Floro, J.A.; Han, J.; Hearne, S.; Hunter, J.; Tsong, I.

    1998-10-14

    The evolution of stress in gallium nitride films on sapphire has been measured in real- time during metal organic chemical vapor deposition. In spite of the 161%0 compressive lattice mismatch of GaN to sapphire, we find that GaN consistently grows in tension at 1050"C. Furthermore, in-situ stress monitoring indicates that there is no measurable relaxation of the tensile growth stress during annealing or thermal cycling.

  4. Mass transport, faceting and behavior of dislocations in GaN

    SciTech Connect

    Nitta, S.; Kashima, T.; Kariya, M.; Yukawa, Y.; Yamaguchi, S.; Amano, H.; Akasaki, I.

    2000-07-01

    The behavior of threading dislocations during mass transport of GaN was investigated in detail by transmission electron microscopy. Mass transport occurred at the surface. Therefore, growing species are supplied from the in-plane direction. The behavior of threading dislocations was found to be strongly affected by the mass transport process as well as the high crystallographic anisotropy of the surface energy of the facets particular to GaN.

  5. Gadolinium-Based GaN for Neutron Detection with Gamma Discrimination

    DTIC Science & Technology

    2016-06-01

    diodes since the proposed neutron convertor is Gd, which emits fast electrons upon neutron capture. Diode N7 appeared to show a good response to a 14C...research. Workable GaN Schottky diode radiation detectors were successfully fabricated and tested. The first year has, however, seen a significant effort...Epitaxy (HVPE) grown GaN substrate (Kyma technology [3]) was employed and the sandwich structure Schottky diode was fabricated, on which both alpha and

  6. Evolution of deep centers in GaN grown by hydride vapor phaseepitaxy

    SciTech Connect

    Fang, Z.-Q.; Look, D.C.; Jasinski, J.; Benamara, M.; Liliental-Weber, Z.; Molnar, R.J.

    2001-04-18

    Deep centers and dislocation densities in undoped n GaN, grown by hydride vapor phase epitaxy (HVPE), were characterized as a function of the layer thickness by deep level transient spectroscopy and transmission electron microscopy, respectively. As the layer thickness decreases, the variety and concentration of deep centers increase, in conjunction with the increase of dislocation density. Based on comparison with electron irradiation induced centers, some dominant centers in HVPE GaN are identified as possible point defects.

  7. Determination of the nitrogen vacancy as a shallow compensating center in GaN doped with divalent metals.

    PubMed

    Buckeridge, J; Catlow, C R A; Scanlon, D O; Keal, T W; Sherwood, P; Miskufova, M; Walsh, A; Woodley, S M; Sokol, A A

    2015-01-09

    We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

  8. Complete Genome Sequence of Salmonella enterica Serovar Typhimurium Strain YU15 (Sequence Type 19) Harboring the Salmonella Genomic Island 1 and Virulence Plasmid pSTV

    PubMed Central

    Calva, Edmundo; Puente, José L.; Zaidi, Mussaret B.

    2016-01-01

    The complete genome of Salmonella enterica subsp. enterica serovar Typhimurium sequence type 19 (ST19) strain YU15, isolated in Yucatán, Mexico, from a human baby stool culture, was determined using PacBio technology. The chromosome contains five intact prophages and the Salmonella genomic island 1 (SGI1). This strain carries the Salmonella virulence plasmid pSTV. PMID:27081132

  9. Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au /GaN Schottky contacts

    NASA Astrophysics Data System (ADS)

    Wang, R. X.; Xu, S. J.; Shi, S. L.; Beling, C. D.; Fung, S.; Zhao, D. G.; Yang, H.; Tao, X. M.

    2006-10-01

    Under identical preparation conditions, Au /GaN Schottky contacts were prepared on two kinds of GaN epilayers with significantly different background electron concentrations and mobility as well as yellow emission intensities. Current-voltage (I-V) and variable-frequency capacitance-voltage (C-V) characteristics show that the Schottky contacts on the GaN epilayer with a higher background carrier concentration and strong yellow emission exhibit anomalous reverse-bias I-V and C-V characteristics. This is attributed to the presence of deep level centers. Theoretical simulation of the low-frequency C-V curves leads to a determination of the density and energy level position of the deep centers.

  10. [Professor ZHANG Yu-Lian's experiences in treatment of post-stroke ataxia by regulating marrow sea acupuncture].

    PubMed

    Zhang, Su-Ling

    2014-08-01

    The experiences and characteristics of professor ZHANG Yu-lian in regulating marrow sea acupuncture for treatment of post-stroke ataxia is introduced. Professor ZHANG established regulating marrow sea acupuncture based on the fundamentals of traditional Chinese medicine combined with brain functional region projection and cerebrovascular distribution of modern medicine. "Three acupoints regulating balance" "3 acupoints regulating transportation" "3 acupoints regulating tremor" and Fengchi (GB 20), Fengfu (GB 16), Wangu (GB 12), Tianzhu (BL 10) and C3-C6 Jiaji (Ex-B2) acupoints were applied in this kind of manipulation. We combined holding spirits of doctor and patient together, and controlled the sensation transduction with different manipulations to reach the foci, which emphasis on the doctor-patient cooperation and body-mind co-regulation, finally promote patients' comprehensive rehabilitation.

  11. Schoolbook Texts: Behavioral Achievement Priming in Math and Language.

    PubMed

    Engeser, Stefan; Baumann, Nicola; Baum, Ingrid

    2016-01-01

    Prior research found reliable and considerably strong effects of semantic achievement primes on subsequent performance. In order to simulate a more natural priming condition to better understand the practical relevance of semantic achievement priming effects, running texts of schoolbook excerpts with and without achievement primes were used as priming stimuli. Additionally, we manipulated the achievement context; some subjects received no feedback about their achievement and others received feedback according to a social or individual reference norm. As expected, we found a reliable (albeit small) positive behavioral priming effect of semantic achievement primes on achievement in math (Experiment 1) and language tasks (Experiment 2). Feedback moderated the behavioral priming effect less consistently than we expected. The implication that achievement primes in schoolbooks can foster performance is discussed along with general theoretical implications.

  12. Schoolbook Texts: Behavioral Achievement Priming in Math and Language

    PubMed Central

    Engeser, Stefan; Baumann, Nicola; Baum, Ingrid

    2016-01-01

    Prior research found reliable and considerably strong effects of semantic achievement primes on subsequent performance. In order to simulate a more natural priming condition to better understand the practical relevance of semantic achievement priming effects, running texts of schoolbook excerpts with and without achievement primes were used as priming stimuli. Additionally, we manipulated the achievement context; some subjects received no feedback about their achievement and others received feedback according to a social or individual reference norm. As expected, we found a reliable (albeit small) positive behavioral priming effect of semantic achievement primes on achievement in math (Experiment 1) and language tasks (Experiment 2). Feedback moderated the behavioral priming effect less consistently than we expected. The implication that achievement primes in schoolbooks can foster performance is discussed along with general theoretical implications. PMID:26938446

  13. Carbon nanotube assisted Lift off of GaN layers on sapphire

    NASA Astrophysics Data System (ADS)

    Long, Hao; Feng, Xiaohui; Wei, Yang; Yu, Tongjun; Fan, Shoushan; Ying, Leiying; Zhang, Baoping

    2017-02-01

    Laser lift off (LLO) was one of the most essential processes in fabrication of vertical GaN-based LEDs. However, traditional laser lift off of GaN on sapphire substrates needed high laser energy threshold, which deteriorated the GaN crystal. In this paper, it was found that inserting carbon nanotube between GaN and sapphire could effectively reduce the laser energy threshold in GaN LLO, from 1.5 J /cm2 of conventional GaN/sapphire to 1.3 J /cm2 of CNT inserted GaN/sapphire. The temperature distributions at the GaN/sapphire interfaces with and without CNTs were simulated by the finite elements calculation under laser irradiation. It was found that, due to the higher laser absorption coefficient of CNT, the CNT played as a powerful heating wire, sending out the thermal outside to elevate the GaN's temperature, and thus reduce the laser threshold for LLO. Raman and photoluminescence measurements indicated that residual stress of GaN membranes was as small as 0.3 GPa by the carbon nanotube assisted LLO. This work not only opens new application of CNTs, but also demonstrates the potential of high performance blue and green LEDs.

  14. Hybrid device based on GaN nanoneedles and MEH-PPV/PEDOT:PSS polymer

    SciTech Connect

    Shin, Min Jeong; Gwon, Dong-Oh; Lee, Chan-Mi; Lee, Gang Seok; Jeon, In-Jun; Ahn, Hyung Soo; Yi, Sam Nyung; Ha, Dong Han

    2015-08-15

    Highlights: • A hybrid device was demonstrated by using MEH-PPV, PEDOT:PSS, and GaN nanoneedles. • I–V curve of the hybrid device showed its rectification behaviour, similar to a diode. • EL peak originated by the different potential barriers at MEH-PPV and GaN interface. - Abstract: A hybrid device that combines the properties of organic and inorganic semiconductors was fabricated and studied. It incorporated poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as organic polymers and GaN nanoneedles as an inorganic semiconductor. Layers of the two polymers were spin coated on to the GaN nanoneedles. The one peak in the electroluminescence spectrum originated from the MEH-PPV layer owing to the different potential barriers of electrons and holes at its interface with the GaN nanoneedles. However, the photoluminescence spectrum showed peaks due to both GaN nanoneedles and MEH-PPV. Such hybrid structures, suitably developed, might be able to improve the efficiency of optoelectronic devices.

  15. Correlation between macroscopic transport parameters and microscopic electrical properties in GaN

    NASA Astrophysics Data System (ADS)

    Witte, H.; Krtschil, A.; Schrenk, E.; Fluegge, K.; Dadgar, A.; Krost, A.

    2005-02-01

    In GaN layers grown by metal-organic vapor phase epitaxy on sapphire substrates the temperature-dependent Hall (TDH) and photo-Hall-effect (PHE) measurements show essential differences between undoped and Si-doped GaN. In undoped GaN the maximum of the Hall mobility occurs at temperatures near 300K with a low value. In PHE, an illumination introduces an enhancement of the mobility and a decrease of the electron density. In contrast, in Si-doped GaN the maximum Hall mobility is higher by a factor of 10 and is observed at temperatures between 100 and 180K. The photoinduced changes in the mobility and electron density are only marginal. Intensity dependent PHE measurements suggest the existence of internal potential barriers caused by inhomogeneities in the undoped samples. These results are combined with the surface-potential roughness on a microscale, as determined by scanning surface-potential microscopy (SSPM). In SSPM the undoped layers show strong potential fluctuations while they are lower for the Si-doped GaN samples. A correlation among the rms roughness of the surface potential, the maximum Hall mobility in TDH, and the maximum changes of the photo-Hall mobility is observed. In undoped GaN the mobility seems to be determined by the scattering at inner potential barriers stemming from structural inhomogeneities.

  16. Strain-induced step bunching in orientation-controlled GaN on Si

    NASA Astrophysics Data System (ADS)

    Narita, Tetsuo; Iguchi, Hiroko; Horibuchi, Kayo; Otake, Nobuyuki; Hoshi, Shinichi; Tomita, Kazuyoshi

    2016-05-01

    We report a technique for the fabrication of high-quality GaN-on-silicon (Si) substrates for use in various power applications. GaN epitaxial layers were generated on Si(111) vicinal faces that had been previously covered with a thin coating of Al2O3 to control the orientation of the AlN seed layers. We obtained orientation-controlled GaN layers and found a linear relationship between the GaN c-axis and Si[111] tilt angles. As a result, the threading dislocation density in the AlN seed layer was reduced and high-quality GaN layers were generated. The X-ray rocking curves for these layers exhibited full width at half maximum values of 390‧‧ and 550‧‧ for the (004) and (114) reflections, respectively. Significant step bunching was observed on a GaN(0001) vicinal face produced using this technique, attributed to strain-induced attractive interactions between steps. Thus, by controlling the strain near the surface layer, we achieved the step flow growth of GaN on Si.

  17. Size dictated thermal conductivity of GaN

    DOE PAGES

    Thomas Edwin Beechem; McDonald, Anthony E.; Fuller, Elliot James; ...

    2016-04-01

    The thermal conductivity on n- and p-type doped gallium nitride (GaN) epilayers having thickness of 3-4 μm was investigated using time domain thermoreflectance (TDTR). Despite possessing carrier concentrations ranging across 3 decades (1015 – 1018 cm–3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends–and their overall reduction relative to bulk–are explained leveraging established scattering models where it is shown that size effects play a primary role in limiting thermal conductivity for layers even tens of microns thick. GaNmore » device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness.« less

  18. Ge doping of GaN beyond the Mott transition

    NASA Astrophysics Data System (ADS)

    Ajay, A.; Schörmann, J.; Jiménez-Rodriguez, M.; Lim, C. B.; Walther, F.; Rohnke, M.; Mouton, I.; Amichi, L.; Bougerol, C.; Den Hertog, M. I.; Eickhoff, M.; Monroy, E.

    2016-11-01

    We present a study of germanium as n-type dopant in wurtzite GaN films grown by plasma-assisted molecular-beam epitaxy, reaching carrier concentrations of up to 6.7  ×  1020 cm-3 at 300 K, well beyond the Mott density. The Ge concentration and free carrier density were found to scale linearly with the Ge flux in the studied range. All the GaN:Ge layers present smooth surface morphology with atomic terraces, without trace of pits or cracks, and the mosaicity of the samples has no noticeable dependence on the Ge concentration. The variation of the GaN:Ge band gap with the carrier concentration is consistent with theoretical calculations of the band gap renormalization due to electron-electron and electron-ion interaction, and Burstein-Moss effect.

  19. Influence of dopants on defect formation in GaN

    SciTech Connect

    Liliental-Weber, Z.; Jasinski, J.; Benamara, M.; Grzegory, I.; Porowski, S.; Lampert, D.J.H.; Eiting, C.J.; Dupuis R.D.

    2001-10-15

    Influence of p-dopants (Mg and Be) on the structure of GaN has been studied using Transmission Electron Microscopy (TEM). Bulk GaN:Mg and GaN:Be crystals grown by a high pressure and high temperature process and GaN:Mg grown by metal-organic chemical-vapor deposition (MOCVD) have been studied. Structural dependence on growth polarity was observed in the bulk crystals. Spontaneous ordering in bulk GaN:Mg on c-plane (formation of Mg-rich planar defects with characteristics of inversion domains) was observed for growth in the N to Ga polar direction (N polarity). On the opposite site of the crystal (growth in the Ga to N polar direction) Mg-rich pyramidal defects empty inside (pinholes) were observed. Both these defects were also observed in MOCVD grown crystals. Pyramidal defects were also observed in the bulk GaN:Be crystals.

  20. Electron spin dynamics in cubic GaN

    NASA Astrophysics Data System (ADS)

    Buß, J. H.; Schupp, T.; As, D. J.; Brandt, O.; Hägele, D.; Rudolph, J.

    2016-12-01

    The electron spin dynamics in cubic GaN is comprehensively investigated by time-resolved magneto-optical Kerr-rotation spectroscopy over a wide range of temperatures, magnetic fields, and doping densities. The spin dynamics is found to be governed by the interplay of spin relaxation of localized electrons and Dyakonov-Perel relaxation of delocalized electrons. Localized electrons significantly contribute to spin relaxation up to room temperature at moderate doping levels, while Dyakonov-Perel relaxation dominates for high temperatures or degenerate doping levels. Quantitative agreement to Dyakonov-Perel theory requires a larger value of the spin-splitting constant than theoretically predicted. Possible reasons for this discrepancy are discussed, including the role of charged dislocations.

  1. Dislocation generation in GaN by dicing process

    NASA Astrophysics Data System (ADS)

    Taguchi, Hideyuki; Kitahara, Amane; Miyake, Syugo; Nakaue, Akimitu; Nishikawa, Atsushi; Fujiwara, Yasufumi

    2013-03-01

    In order to analyze effect of the dicing process on the GaN epitaxial layer, the GaN-wafer is cut in sizes of the 0.7 mm square and the 1.7 mm square. The crystal characteristics of the GaN-chips have been measured using X-ray measurements and Raman spectra measurements. The full-width half maximum (FWHM) values of the X-ray rocking curves of (0002), (10-13) and (10-12) of the 0.7 mm square GaN-chip become wider than that of before the dicing process. The E2 (high) peak of Raman spectra at the edge in the 0.7mm square GaN-chip is shifted to lower wave number. In consideration of crystallography, we infer from these results that both the crystal strains and the screw dislocations have been generated during the dicing process.

  2. Intrinsic polarization control in rectangular GaN nanowire lasers

    DOE PAGES

    Li, Changyi; Liu, Sheng; Luk, Ting S.; ...

    2016-02-01

    In this study, we demonstrate intrinsic, linearly polarized lasing from single GaN nanowires using cross-sectional shape control. A two-step top-down fabrication approach was employed to create straight nanowires with controllable rectangular cross-sections. A clear lasing threshold of 444kW/cm2 and a narrow spectral line width of 0.16 nm were observed under optical pumping at room temperature, indicating the onset of lasing. The polarization was along the short dimension (y-direction) of the nanowire due to the higher transverse confinement factors for y-polarized transverse modes resulting from the rectangular nanowire cross-section. The results show that cross-sectioned shape control can enable inherent control overmore » the polarization of nanowire lasers without additional environment requirements, such as placement onto lossy substrates.« less

  3. Intrinsic polarization control in rectangular GaN nanowire lasers

    SciTech Connect

    Li, Changyi; Liu, Sheng; Luk, Ting S.; Figiel, Jeffrey J.; Brener, Igal; Brueck, S. R. J.; Wang, George T.

    2016-02-01

    In this study, we demonstrate intrinsic, linearly polarized lasing from single GaN nanowires using cross-sectional shape control. A two-step top-down fabrication approach was employed to create straight nanowires with controllable rectangular cross-sections. A clear lasing threshold of 444kW/cm2 and a narrow spectral line width of 0.16 nm were observed under optical pumping at room temperature, indicating the onset of lasing. The polarization was along the short dimension (y-direction) of the nanowire due to the higher transverse confinement factors for y-polarized transverse modes resulting from the rectangular nanowire cross-section. The results show that cross-sectioned shape control can enable inherent control over the polarization of nanowire lasers without additional environment requirements, such as placement onto lossy substrates.

  4. Spontaneous emission enhancement in micropatterned GaN

    NASA Astrophysics Data System (ADS)

    Niehus, M.; Sanguino, P.; Monteiro, T.; Soares, M. J.; Schwarz, R.

    2004-10-01

    With two interfering pulses from the fourth harmonic of a Nd-YAG laser we burnt a periodic lattice structure into the surface of GaN thin films. The lattice period of this permanent grating could be controlled between less than one and several tens of microns. Above the decomposition threshold, nitrogen evades from the sample surface, and the residual metallic gallium accumulates in the form of tiny droplets at the surfaces. The patterned structure shows structural similarities with microcavities. The question arises if the residual metallic gallium may act as a partially reflecting mirror. To test this hypothesis, we studied the steady-state and transient photoluminescence through the modulation of light emerging from the ubiquitous broad "yellow" photoluminescence band. The microlattice is evidenced by energy-equidistant spontaneous emission enhancement peaks in the steady-state photoluminescence spectra. We suggest that the partial reflection due to the residual metallic gallium leads to the observed enhancement effect.

  5. Microstructure of laterally overgrown GaN layers

    SciTech Connect

    Liliental-Weber, Zuzanna; Cherns, David

    2001-04-03

    Transmission electron microscopy study of plan-view and cross-section samples of epitaxial laterally overgrown (ELOG) GaN samples is described. Two types of dislocation with the same type of Burgers vector but different line direction have been observed. It is shown that threading edge dislocations bend to form dislocation segments in the c-plane as a result of shear stresses developed in the wing material along the stripe direction. It is shown that migration of these dislocations involves both glide and climb. Propagation of threading parts over the wing area is an indication of high density of point defects present in the wing areas on the ELOG samples. This finding might shed new light on the optical properties of such samples.

  6. Descendants of primed Arabidopsis plants exhibit resistance to biotic stress.

    PubMed

    Slaughter, Ana; Daniel, Xavier; Flors, Victor; Luna, Estrella; Hohn, Barbara; Mauch-Mani, Brigitte

    2012-02-01

    An attack of plants by pathogens or treatment with certain resistance-inducing compounds can lead to the establishment of a unique primed state of defense. Primed plants show enhanced defense reactions upon further challenge with biotic or abiotic stress. Here, we report that the primed state in Arabidopsis (Arabidopsis thaliana) is still functional in the next generation without additional treatment. We compared the reactions of Arabidopsis plants that had been either primed with β-amino-butyric acid (BABA) or with an avirulent isolate of the bacteria Pseudomonas syringae pv tomato (PstavrRpt2). The descendants of primed plants showed a faster and higher accumulation of transcripts of defense-related genes in the salicylic acid signaling pathway and enhanced disease resistance upon challenge inoculation with a virulent isolate of P. syringae. In addition, the progeny of primed plants was also more resistant against the oomycete pathogen Hyaloperonospora arabidopsidis. When transgenerationally primed plants were subjected to an additional priming treatment, their descendants displayed an even stronger primed phenotype, suggesting that plants can inherit a sensitization for the priming phenomenon. Interestingly, this primed to be primed phenotype was much reduced in the Arabidopsis β-amino-butyric acid priming mutant ibs1 (induced BABA sterility1). Our results demonstrate that the primed state of plants is transferred to their progeny and confers improved protection from pathogen attack as compared to the descendants of unprimed plants.

  7. Contrasts of atmospheric circulation and associated tropical convection between Huaihe River valley and Yangtze River valley mei-yu flooding

    NASA Astrophysics Data System (ADS)

    Hong, Jieli; Liu, Yimin

    2012-07-01

    The significant differences of atmospheric circulation between flooding in the Huaihe and Yangtze River valleys during early mei-yu (i.e., the East Asian rainy season in June) and the related tropical convection were investigated. During the both flooding cases, although the geopotential height anomalies always exhibit equivalent barotropic structures in middle to high latitudes at middle and upper troposphere, the phase of the Rossby wave train is different over Eurasian continent. During flooding in the Huaihe River valley, only one single blocking anticyclone is located over Baikal Lake. In contrast, during flooding in the Yangtze River valley, there are two blocking anticyclones. One is over the Ural Mountains and the other is over Northeast Asia. In the lower troposphere a positive geopotential height anomaly is located at the western ridge of subtropical anticyclone over Western Pacific (SAWP) in both flooding cases, but the location of the height anomaly is much farther north and west during the Huaihe River mei-yu flooding. Furthermore, abnormal rainfall in the Huaihe River valley and the regions north of it in China is closely linked with the latent heating anomaly over the Arabian Sea and Indian peninsula. However, the rainfall in the Yangtze River valley and the regions to its south in China is strongly related to the convection over the western tropical Pacific. Numerical experiments demonstrated that the enhanced latent heating over the Arabian Sea and Indian peninsula causes water vapor convergence in the region south of Tibetan Plateau and in the Huaihe River valley extending to Japan Sea with enhanced precipitation; and vapor divergence over the Yangtze River valley and the regions to its south with deficient precipitation. While the weakened convection in the tropical West Pacific results in moisture converging over the Yangtze River and the region to its south, along with abundant rainfall.

  8. GaN Based Electronics And Their Applications

    NASA Astrophysics Data System (ADS)

    Ren, Fan

    2002-03-01

    The Group III-nitrides were initially researched for their promise to fill the void for a blue solid state light emitter. Electronic devices from III-nitrides have been a more recent phenomenon. The thermal conductivity of GaN is three times that of GaAs. For high power or high temperature applications, good thermal conductivity is imperative for heat removal or sustained operation at elevated temperatures. The development of III-N and other wide bandgap technologies for high temperature applications will likely take place at the expense of competing technologies, such as silicon-on-insulator (SOI), at moderate temperatures. At higher temperatures (>300°C), novel devices and components will become possible. The automotive industry will likely be one of the largest markets for such high temperature electronics. One of the most noteworthy advantages for III-N materials over other wide bandgap semiconductors is the availability of AlGaN/GaN and InGaN/GaN heterostructures. A 2-dimensional electron gas (2DEG) has been shown to exist at the AlGaN/GaN interface, and heterostructure field effect transistors (HFETs) from these materials can exhibit 2DEG mobilities approaching 2000 cm2 / V?s at 300K. Power handling capabilities of 12 W/mm appear feasible, and extraordinary large signal performance has already been demonstrated, with a current state-of-the-art of >10W/mm at X-band. In this talk, high speed and high temperature AlGaN/GaN HEMTs as well as MOSHEMTs, high breakdown voltage GaN (>6KV) and AlGaN (9.7 KV) Schottky diodes, and their applications will be presented.

  9. Zn-dopant dependent defect evolution in GaN nanowires

    NASA Astrophysics Data System (ADS)

    Yang, Bing; Liu, Baodan; Wang, Yujia; Zhuang, Hao; Liu, Qingyun; Yuan, Fang; Jiang, Xin

    2015-10-01

    Zn doped GaN nanowires with different doping levels (0, <1 at%, and 3-5 at%) have been synthesized through a chemical vapor deposition (CVD) process. The effect of Zn doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a hexagonal wurtzite (WZ) structure with good crystallinity. Several kinds of twin boundaries, including (101&cmb.macr;3), (101&cmb.macr;1) and (202&cmb.macr;1), as well as Type I stacking faults (...ABABC&cmb.b.line;BCB...), are observed in the nanowires. The increasing Zn doping level (<1 at%) induces the formation of screw dislocations featuring a predominant screw component along the radial direction of the GaN nanowires. At high Zn doping level (3-5 at%), meta-stable cubic zinc blende (ZB) domains are generated in the WZ GaN nanowires. The WZ/ZB phase boundary (...ABABAC&cmb.b.line;BA...) can be identified as Type II stacking faults. The density of stacking faults (both Type I and Type II) increases with increasing the Zn doping levels, which in turn leads to a rough-surface morphology in the GaN nanowires. First-principles calculations reveal that Zn doping will reduce the formation energy of both Type I and Type II stacking faults, favoring their nucleation in GaN nanowires. An understanding of the effect of Zn doping on the defect evolution provides an important method to control the microstructure and the electrical properties of p-type GaN nanowires.Zn doped GaN nanowires with different doping levels (0, <1 at%, and 3-5 at%) have been synthesized through a chemical vapor deposition (CVD) process. The effect of Zn doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a

  10. Prime factorization using magnonic holographic devices

    NASA Astrophysics Data System (ADS)

    Khivintsev, Yuri; Ranjbar, Mojtaba; Gutierrez, David; Chiang, Howard; Kozhevnikov, Alexander; Filimonov, Yuri; Khitun, Alexander

    2016-09-01

    Determining the prime factors of a given number N is a problem that requires super-polynomial time for conventional digital computers. A polynomial-time algorithm was invented by Shor for quantum computers. In this paper, we present experimental data that demonstrate prime factorization using spin-wave interference but without quantum entanglement. Prime factorization includes three major steps. First, a general-type computer calculates the sequence of numbers mkmod(N), where N is the number to be factorized, m is a randomly chosen positive integer, and k = 1, 2, 3, 4, 5, 6…. Next, the period of the calculated sequence r is determined by exploiting spin-wave interference. Finally, the general-type computer determines the primes based on the obtained r. The experiment for period finding was conducted on a six-terminal Y3Fe2(FeO4)3 device. We chose number 15 for testing and determined its primes using a sequence of measurements. The obtained experimental data for a micrometer-sized prototype aimed to demonstrate the benefits of using spin-wave devices to solve complex computational problems. Scalability is one of the major strengths inherent in this type of wave-based device, which may provide a route to nanometer-sized logic circuits. We discuss the physical and technological limitations of this approach, which define the maximum size of N and the computational speed. Although this classical approach cannot compete with the quantum algorithm in terms of efficiency, magnonic holographic devices can potentially be used as complementary logic units aimed at speeding up prime factorization for classical computers.

  11. Mare Orientale Prime Meridian lunar coordinate system

    NASA Astrophysics Data System (ADS)

    Walden, B.; York, C.; McGown, R.; Billings, T.

    The Moon was the first extraterrestrial body to be mapped. From 1514 to 1840, navigators sailing the open seas needed accurate lunar maps to determine longitude by the "lunar-distance" method. For the convenience of early navigators, astronomers and selenographers, the lunar prime meridian was made to bisect the lunar disk as seen from Earth, formalized as the present Mean Earth / Polar Axis system. In 1961, the International Astronomical Union reversed lunar east and west to avoid confusion by astronauts and their controllers, so that now Mare Orientale -- the Eastern Sea -- lies on the Moon's western limb. By international agreement in 1974, lunar longitude was defined to increase eastward from zero to 360 degrees and prime meridians are generally defined by an observable feature. Examination of popular lunar maps indicates these newer standards are not widely accepted. Modern navigation no longer relies on the Moon. Lunar maps are now made by satellite imagery from lunar orbit. Today, humankind anticipates navigating the Moon itself. A relatively simple change to the lunar coordinate system could benefit upcoming lunar activities and promote acceptance of a 360 degree standard: move the lunar prime meridian. We propose the lunar prime meridian intersect some natural monument that most nearly represents the center longitude of Mare Orientale (perhaps crater Hohmann), and longitude increase eastward from zero to 360 degrees. Mare Orientale is a dramatic large "target," easily identifiable from space. Nearside traffic will use low longitude numbers from zero to r ughly 180 degrees,o and will not frequently cross this prime meridian. Earth's angle above the eastern horizon equals approximate longitude. Low and high longitude numbers will reflect the distinctive nearside and farside geological domains. The face of the Moon as seen from Earth will no longer be split in two. Calculations are simplified and sources of error eliminated. This system is more convenient and

  12. High electron mobility GaN grown under N-rich conditions by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Koblmueller, G.; Wu, F.; Mates, T.; Speck, J. S.; Fernandez-Garrido, S.; Calleja, E.

    2007-11-26

    An alternative approach is presented for the plasma-assisted molecular beam epitaxy of high-quality GaN. Under N-rich growth conditions, an unexpected layer-by-layer growth mode was found for a wide range of growth temperatures in the GaN thermal decomposition regime (>750 deg. C). Consequently, superior surface morphologies with roughness of less than 1 nm (rms) have been achieved. For lightly Si-doped GaN films, room-temperature electron mobilities exceeding 1100 cm{sup 2}/V s were measured, surpassing the commonly insulating nature of GaN grown under N-rich conditions at low temperature.

  13. A growth diagram for plasma-assisted molecular beam epitaxy of GaN nanocolumns on Si(111)

    SciTech Connect

    Fernandez-Garrido, S.; Grandal, J.; Calleja, E.; Sanchez-Garcia, M. A.; Lopez-Romero, D.

    2009-12-15

    The morphology of GaN samples grown by plasma-assisted molecular beam epitaxy on Si(111) was systematically studied as a function of impinging Ga/N flux ratio and growth temperature (730-850 deg. C). Two different growth regimes were identified: compact and nanocolumnar. A growth diagram was established as a function of growth parameters, exhibiting the transition between growth regimes, and showing under which growth conditions GaN cannot be grown due to thermal decomposition and Ga desorption. Present results indicate that adatoms diffusion length and the actual Ga/N ratio on the growing surface are key factors to achieve nanocolumnar growth.

  14. High-resistivity GaN buffer templates and their optimization for GaN-based HFETs

    NASA Astrophysics Data System (ADS)

    Hubbard, S. M.; Zhao, G.; Pavlidis, D.; Sutton, W.; Cho, E.

    2005-11-01

    High-resistance (HR) GaN templates for AlGaN/GaN heterojunction field effect transistor (HFET) applications were grown using organometallic vapor phase epitaxy. The GaN sheet resistance was tuned using final nucleation layer (NL) annealing temperature and NL thickness. Using an annealing temperature of 1033 °C and NL thickness of 26 nm, GaN with sheet resistance of 10 10 Ω/sq was achieved, comparable to that of Fe-doped GaN. Material characterization results show that the high-resistance GaN is achieved due to compensating acceptor levels that may be introduced through edge-type threading dislocations. Optimization of annealing temperature and NL thickness provided a means to maximize GaN sheet resistance without significantly degrading material quality. In situ laser reflectance was used to correlate the NL properties to sheet resistance and material quality, providing a figure of merit for expected sheet resistance. AlGaN/GaN HFET layers grown using HR GaN templates with R of 10 10 Ω/sq gave surface and interface roughness of 14 and 7 Å, respectively. The 2DEG Hall mobility and sheet charge of HFETs grown using HR GaN templates was comparable to similar layers grown using unintentionally doped (UID) GaN templates.

  15. Crystallographic Wet Chemical Etching of Semipolar GaN (11-22) Grown on m-Plane Sapphire Substrates.

    PubMed

    Kim, Jae-Kwan; Lee, Sung Nam; Song, Keun-Man; Yoon, Jae-Sik; Lee, Ji-Myon

    2015-07-01

    This paper reports the etch rates and etched surface morphology of semipolar GaN using a potassium hydroxide (KOH) solution. Semipolar (11-22) GaN could be etched easily using a KOH solution and the etch rate was higher than that of Ga-polar c-plane GaN (0001). The etch rate was anisotropic and the highest etch rate was measured to be approximately 116 nm/min for the (1011) plane and 62 nm/min for the (11-20) plane GaN using a 4 M KOH solution at 100 °C, resulting in specific surface features, such as inclined trigonal cells.

  16. Growth and characterization of GaN thin films on Si(111) substrates using SiC intermediate layer

    SciTech Connect

    Lim, K.Y.; Lee, K.J.; Park, C.I.; Kim, K.C.; Choi, S.C.; Lee, W.H.; Suh, E.K.; Yang, G.M.; Nahm, K.S.

    2000-07-01

    GaN films have been grown atop Si-terminated 3C-SiC intermediate layer on Si(111) substrates using low pressure metalorganic chemical vapor deposition (LP-MOCVD). The SiC intermediate layer was grown by chemical vapor deposition (CVD) using tetramethylsilane (TMS) as the single source precursor. The Si terminated SiC surface was obtained by immediately flow of SiH{sub 4} gas after growth of SiC film. LP-MOCVD growth of GaN on 3C-SiC/Si(111) was carried out with trimethylgallium (TMG) and NH{sub 3}. Single crystalline hexagonal GaN layers can be grown on Si terminated SiC intermediate layer using an AlN or GaN buffer layer. Compared with GaN layers grown using a GaN buffer layer, the crystal qualities of GaN films with AlN buffer layers are extremely improved. The GaN films were characterized by x-ray diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). Full width at half maximum (FWHM) of double crystal x-ray diffraction (DCXD) rocking curve for GaN (0002) on 3C-SiC/Si(111) was 890 arcsec. PL near band edge emission peak position and FWHM at room temperature are 3.38 eV and 79.35 meV, respectively.

  17. Retro-priming, priming, and double testing: psi and replication in a test–retest design

    PubMed Central

    Rabeyron, Thomas

    2014-01-01

    Numerous experiments have been conducted in recent years on anomalous retroactive influences on cognition and affect (Bem, 2010), yet more data are needed to understand these processes precisely. For this purpose, we carried out an initial retro-priming study in which the response times of 162 participants were measured (Rabeyron and Watt, 2010). In the current paper, we present the results of a second study in which we selected those participants who demonstrated the strongest retro-priming effect during the first study, in order to see if we could replicate this effect and therefore select high scoring participants. An additional objective was to try to find correlations between psychological characteristics (anomalous experiences, mental health, mental boundaries, trauma, negative life events) and retro-priming results for the high scoring participants. The retro-priming effect was also compared with performance on a classical priming task. Twenty-eight participants returned to the laboratory for this new study. The results, for the whole group, on the retro-priming task, were negative and non-significant (es = −0.25, ns) and the results were significant on the priming task (es = 0.63, p < 0.1). We obtained overall negative effects on retro-priming results for all the sub-groups (students, male, female). Ten participants were found to have positive results on the two retro-priming studies, but no specific psychological variables were found for these participants compared to the others. Several hypotheses are considered in explaining these results, and the author provide some final thoughts concerning psi and replicability. PMID:24672466

  18. High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

    SciTech Connect

    McSkimming, Brian M. Speck, James S.; Chaix, Catherine

    2015-09-15

    In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N{sub 2} gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 10{sup 16} and ∼5 × 10{sup 17}, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.

  19. Emergence, Self-Organization and Prime Numbers

    NASA Astrophysics Data System (ADS)

    Berezin, Alexander A.

    1998-04-01

    Pattern of primes (PP) is critical for dynamics of universal emergence, self-organization and complexity ascendance [1-3]. Due to gradual logarithmic dilution of primes (prime number theorem), PP gives only base envelop for above effects. More informative are full factorizational spectra (FS) of all intermediate composites. Tower exponential mappings like f(N) = 10(N)10 with (N) indicating N vertical arrows [4] lead to infinite fractal-like hierarchy of integer trails; say, FS of intervals between f(N) and f(N+1). This allows FAPP-infinite informational content of PP and FS be "used" as catalyzer of emergence dynamics. This is "Platonic pressure effect" (physical embodiments of PP and FS). Said effect may provide more direct picture for cosmogenesis than traditional quantum tunneling ("Big Bang") and/or inflationary scenarios. Furthermore, we can speculate that metrics of (Mega)universe at tower exponential scales becomes asymptotically Euclidean (multi or infinitely dimensional), due to unchangability of PP and FS. - [1] Arnold Arnold, "The Corrupted Sciences", Paladin (Harper Collins), 1992; [2] Peter Plichta, "God's Secret Formula: Deciphering the Riddle of the Universe and the Prime Number Code", Element, 1997; [3] Alexander Berezin, URAM Journal, 20, 72 (1997); [4] Donald E. Knuth, Science, 194, 1235, 17 Dec 1976. abstract.

  20. Values in Prime-Time Television.

    ERIC Educational Resources Information Center

    Selnow, Gary W.

    1990-01-01

    Describes how values are portrayed on prime-time network television. Looks at the prominence of values incidents in a story line and at how fully the values are explained. Examines how values incidents are structured and linked. Concludes that values incidents play an integral, if not principal, role in television programs. (RS)

  1. Maple Explorations, Perfect Numbers, and Mersenne Primes

    ERIC Educational Resources Information Center

    Ghusayni, B.

    2005-01-01

    Some examples from different areas of mathematics are explored to give a working knowledge of the computer algebra system Maple. Perfect numbers and Mersenne primes, which have fascinated people for a very long time and continue to do so, are studied using Maple and some questions are posed that still await answers.

  2. Tcf15 Primes Pluripotent Cells for Differentiation

    PubMed Central

    Davies, Owen R.; Lin, Chia-Yi; Radzisheuskaya, Aliaksandra; Zhou, Xinzhi; Taube, Jessica; Blin, Guillaume; Waterhouse, Anna; Smith, Andrew J.H.; Lowell, Sally

    2013-01-01

    Summary The events that prime pluripotent cells for differentiation are not well understood. Inhibitor of DNA binding/differentiation (Id) proteins, which are inhibitors of basic helix-loop-helix (bHLH) transcription factor activity, contribute to pluripotency by blocking sequential transitions toward differentiation. Using yeast-two-hybrid screens, we have identified Id-regulated transcription factors that are expressed in embryonic stem cells (ESCs). One of these, Tcf15, is also expressed in the embryonic day 4.5 embryo and is specifically associated with a novel subpopulation of primed ESCs. An Id-resistant form of Tcf15 rapidly downregulates Nanog and accelerates somatic lineage commitment. We propose that because Tcf15 can be held in an inactive state through Id activity, it may prime pluripotent cells for entry to somatic lineages upon downregulation of Id. We also find that Tcf15 expression is dependent on fibroblast growth factor (FGF) signaling, providing an explanation for how FGF can prime for differentiation without driving cells out of the pluripotent state. PMID:23395635

  3. A Fresh Approach to Prime Numbers.

    ERIC Educational Resources Information Center

    Hampton, Homer F.

    1979-01-01

    The introduction of prime numbers in the intermediate grades should be handled with care or the concept will appear arbitrary, artificial, and unreal to the pupils. The approach suggested here is in the form of a game-like activity. A knowledge of multiplication and factors is a prerequisite. (BB)

  4. Attentional Control and Asymmetric Associative Priming

    ERIC Educational Resources Information Center

    Hutchison, Keith A.; Heap, Shelly J.; Neely, James H.; Thomas, Matthew A.

    2014-01-01

    Participants completed a battery of 3 attentional control (AC) tasks (OSPAN, antisaccade, and Stroop, as in Hutchison, 2007) and performed a lexical decision task with symmetrically associated (e.g., "sister-brother") and asymmetrically related primes and targets presented in both the forward (e.g., "atom-bomb") and backward…

  5. Predicting the Unbeaten Path through Syntactic Priming

    ERIC Educational Resources Information Center

    Arai, Manabu; Nakamura, Chie; Mazuka, Reiko

    2015-01-01

    A number of previous studies showed that comprehenders make use of lexically based constraints such as subcategorization frequency in processing structurally ambiguous sentences. One piece of such evidence is lexically specific syntactic priming in comprehension; following the costly processing of a temporarily ambiguous sentence, comprehenders…

  6. Thematic Mathematics: The Combinatorics of Prime Factorizations

    ERIC Educational Resources Information Center

    Griffiths, Martin

    2010-01-01

    In this article, we use a particular example to illustrate a thematic approach to the teaching and learning of mathematics. Our theme, suitable for undergraduates and able sixth-form students, is the enumeration of mathematical objects associated with the prime factorizations of integers. It is shown in detail how this gives rise to some beautiful…

  7. Phonological Priming and Cohort Effects in Toddlers

    ERIC Educational Resources Information Center

    Mani, Nivedita; Plunkett, Kim

    2011-01-01

    Adult word recognition is influenced by prior exposure to phonologically or semantically related words ("cup" primes "cat" or "plate") compared to unrelated words ("door"), suggesting that words are organised in the adult lexicon based on their phonological and semantic properties and that word recognition implicates not just the heard word, but…

  8. Values in Prime Time Alcoholic Beverage Commercials.

    ERIC Educational Resources Information Center

    Frazer, Charles F.

    Content analysis was used to study the values evident in televised beer and wine commercials. Seventy-seven prime time commercials, 7.6% of a week's total, were analyzed along value dimensions adapted from Gallup's measure of popular social values. The intensity of each value was coded on a five-point scale. None of the commercials in the beer and…

  9. PRIME: probing the very early universe

    NASA Astrophysics Data System (ADS)

    Zheng, Wei; Ford, Holland C.; Kruk, Jeffrey W.; Tsvetanov, Zlatan I.; Szalay, Alexander; Hartig, George F.; Stockman, Hervey S.; Postman, Marc; Voit, G. M.; Shu, Peter K.; Greenhouse, Matthew A.; Rix, Hans-Walter; Lenzen, Rainer; Kent, Steven M.; Stoughton, Christopher; Omont, Alain; Mellier, Yannick

    2003-03-01

    PRIME (The Primordial Explorer) is a proposed Explorer-class mission. It will carry out a deep sky survey from space in four near-infrared bands between ~0.9-3.5 μm. It surveys a quarter of the sky to AB magnitude of ~24, which is ~600 times deeper than 2MASS and ~ five million times deeper than COBE at long wavelengths. Deeper surveys in selected sky regions are also planned. PRIME will reach an epoch during which the first quasars, galaxies and clusters of galaxies were formed in the early universe, map the large-scale structure of the dark matter, discover Type-Ia supernovae to be used in measuring the acceleration of the expanding universe, and detect thousands of brown dwarfs and even Jupiter-size planets in the vicinity of the solar system. Most of these objects are so rare that they may be identified only in large and deep surveys. PRIME will serve as the precursor for the Next Generation Space Telescope (NGST), supplying rare targets for its spectroscopy and deep imaging. It is more than capable of providing targets for the largest ground-based telescopes (10-30m). Combining PRIME with other surveys (SDSS, GALEX) will yield the largest astronomical database ever built.

  10. PRIMING THE PUMP AND CONTROLLING THE FLOW.

    ERIC Educational Resources Information Center

    BUCHAN, VIVIAN

    THE BEGINNING WRITER NEEDS BOTH ENCOURAGEMENT AND DIRECTION. ONCE A STUDENT, NONVERBAL OR FLUENT, HAS EXPRESSED AN OPINION, SIGNIFICANT OR TRIVIAL, THE PUMP CAN BE PRIMED BY ASKING HIM "WHY," AND HIS FLOW OF "BECAUSES" CAN BE CONTROLLED BY CHANNELING THEM INTO A SIMPLE PATTERN. THE NONVERBAL STUDENT IS ENCOURAGED TO WRITE WHEN HE LEARNS THAT A…

  11. Comparison of affective and semantic priming in different SOA.

    PubMed

    Jiang, Zhongqing; Qu, Yuhong; Xiao, Yanli; Wu, Qi; Xia, Likun; Li, Wenhui; Liu, Ying

    2016-11-01

    Researchers have been at odds on whether affective or semantic priming is faster or stronger. The present study selects a series of facial expression photos and words, which have definite emotional meaning or gender meaning, to set up experiment including both affective and semantic priming. The intensity of emotion and gender information in the prime as well as the strength of emotional or semantic (in gender) relationship between the prime and the target is matched. Three groups of participants are employed separately in our experiment varied with stimulus onset asynchrony (SOA) as 50, 250 or 500 ms. The results show that the difference between two types of priming effect is revealed when the SOA is at 50 ms, in which the affective priming effect is presented when the prime has negative emotion. It indicates that SOA can affect the comparison between the affective and semantic priming, and the former takes the priority in the automatic processing level.

  12. Semantic priming without association: a meta-analytic review.

    PubMed

    Lucas, M

    2000-12-01

    A meta-analysis of 26 studies indicated that automatic semantic priming can occur without association. Priming did not vary substantially with differences in variables that affect automatic versus strategic processing, such as time spent processing the prime and target, relationship proportion, and task (except that average effects were smaller in the naming task). Although category coordinates were investigated in the majority of studies, synonyms, antonyms, and script relations also demonstrated priming; functional relations showed greater priming, and essential and perceptual relations showed less. The average effect size for semantic priming was smaller than that for associative priming, suggesting that there is an "associative boost" from adding an associative relationship to a semantic one. The implications of these findings for the modularity thesis and for models of semantic priming are discussed.

  13. Piezo-generator integrating a vertical array of GaN nanowires

    NASA Astrophysics Data System (ADS)

    Jamond, N.; Chrétien, P.; Houzé, F.; Lu, L.; Largeau, L.; Maugain, O.; Travers, L.; Harmand, J. C.; Glas, F.; Lefeuvre, E.; Tchernycheva, M.; Gogneau, N.

    2016-08-01

    We demonstrate the first piezo-generator integrating a vertical array of GaN nanowires (NWs). We perform a systematic multi-scale analysis, going from single wire properties to macroscopic device fabrication and characterization, which allows us to establish for GaN NWs the relationship between the material properties and the piezo-generation, and to propose an efficient piezo-generator design. The piezo-conversion of individual MBE-grown p-doped GaN NWs in a dense array is assessed by atomic force microscopy (AFM) equipped with a Resiscope module yielding an average output voltage of 228 ± 120 mV and a maximum value of 350 mV generated per NW. In the case of p-doped GaN NWs, the piezo-generation is achieved when a positive piezo-potential is created inside the nanostructures, i.e. when the NWs are submitted to compressive deformation. The understanding of the piezo-generation mechanism in our GaN NWs, gained from AFM analyses, is applied to design a piezo-generator operated under compressive strain. The device consists of NW arrays of several square millimeters in size embedded into spin-on glass with a Schottky contact for rectification and collection of piezo-generated carriers. The generator delivers a maximum power density of ˜12.7 mW cm-3. This value sets the new state of the art for piezo-generators based on GaN NWs and more generally on nitride NWs, and offers promising prospects for the use of GaN NWs as high-efficiency ultra-compact energy harvesters.

  14. Piezo-generator integrating a vertical array of GaN nanowires.

    PubMed

    Jamond, N; Chrétien, P; Houzé, F; Lu, L; Largeau, L; Maugain, O; Travers, L; Harmand, J C; Glas, F; Lefeuvre, E; Tchernycheva, M; Gogneau, N

    2016-08-12

    We demonstrate the first piezo-generator integrating a vertical array of GaN nanowires (NWs). We perform a systematic multi-scale analysis, going from single wire properties to macroscopic device fabrication and characterization, which allows us to establish for GaN NWs the relationship between the material properties and the piezo-generation, and to propose an efficient piezo-generator design. The piezo-conversion of individual MBE-grown p-doped GaN NWs in a dense array is assessed by atomic force microscopy (AFM) equipped with a Resiscope module yielding an average output voltage of 228 ± 120 mV and a maximum value of 350 mV generated per NW. In the case of p-doped GaN NWs, the piezo-generation is achieved when a positive piezo-potential is created inside the nanostructures, i.e. when the NWs are submitted to compressive deformation. The understanding of the piezo-generation mechanism in our GaN NWs, gained from AFM analyses, is applied to design a piezo-generator operated under compressive strain. The device consists of NW arrays of several square millimeters in size embedded into spin-on glass with a Schottky contact for rectification and collection of piezo-generated carriers. The generator delivers a maximum power density of ∼12.7 mW cm(-3). This value sets the new state of the art for piezo-generators based on GaN NWs and more generally on nitride NWs, and offers promising prospects for the use of GaN NWs as high-efficiency ultra-compact energy harvesters.

  15. Crystallographically tilted and partially strain relaxed GaN grown on inclined {111} facets etched on Si(100) substrate

    NASA Astrophysics Data System (ADS)

    Ansah Antwi, K. K.; Soh, C. B.; Wee, Q.; Tan, Rayson J. N.; Yang, P.; Tan, H. R.; Sun, L. F.; Shen, Z. X.; Chua, S. J.

    2013-12-01

    High resolution X-ray diffractometry (HR-XRD), Photoluminescence, Raman spectroscopy, and Transmission electron microscope measurements are reported for GaN deposited on a conventional Si(111) substrate and on the {111} facets etched on a Si(100) substrate. HR-XRD reciprocal space mappings showed that the GaN(0002) plane is tilted by about 0.63° ± 0.02° away from the exposed Si{111} growth surface for GaN deposited on the patterned Si(100) substrate, while no observable tilt existed between the GaN(0002) and Si(111) planes for GaN deposited on the conventional Si(111) substrate. The ratio of integrated intensities of the yellow to near band edge (NBE) luminescence (IYL/INBE) was determined to be about one order of magnitude lower in the case of GaN deposited on the patterned Si(100) substrate compared with GaN deposited on the conventional Si(111) substrate. The Raman E2(high) optical phonon mode at 565.224 ± 0.001 cm-1 with a narrow full width at half maximum of 1.526 ± 0.002 cm-1 was measured, for GaN deposited on the patterned Si(100) indicating high material quality. GaN deposition within the trench etched on the Si(100) substrate occurred via diffusion and mass-transport limited mechanism. This resulted in a differential GaN layer thickness from the top (i.e., 1.8 μm) of the trench to the bottom (i.e., 0.3 μm) of the trench. Mixed-type dislocation constituted about 80% of the total dislocations in the GaN grown on the inclined Si{111} surface etched on Si(100).

  16. Crystallographically tilted and partially strain relaxed GaN grown on inclined (111) facets etched on Si(100) substrate

    SciTech Connect

    Ansah Antwi, K. K.; Soh, C. B.; Wee, Q.; Tan, Rayson J. N.; Tan, H. R.; Yang, P.; Sun, L. F.; Shen, Z. X.; Chua, S. J.

    2013-12-28

    High resolution X-ray diffractometry (HR-XRD), Photoluminescence, Raman spectroscopy, and Transmission electron microscope measurements are reported for GaN deposited on a conventional Si(111) substrate and on the (111) facets etched on a Si(100) substrate. HR-XRD reciprocal space mappings showed that the GaN(0002) plane is tilted by about 0.63° ± 0.02° away from the exposed Si(111) growth surface for GaN deposited on the patterned Si(100) substrate, while no observable tilt existed between the GaN(0002) and Si(111) planes for GaN deposited on the conventional Si(111) substrate. The ratio of integrated intensities of the yellow to near band edge (NBE) luminescence (I{sub YL}/I{sub NBE}) was determined to be about one order of magnitude lower in the case of GaN deposited on the patterned Si(100) substrate compared with GaN deposited on the conventional Si(111) substrate. The Raman E{sub 2}(high) optical phonon mode at 565.224 ± 0.001 cm{sup −1} with a narrow full width at half maximum of 1.526 ± 0.002 cm{sup −1} was measured, for GaN deposited on the patterned Si(100) indicating high material quality. GaN deposition within the trench etched on the Si(100) substrate occurred via diffusion and mass-transport limited mechanism. This resulted in a differential GaN layer thickness from the top (i.e., 1.8 μm) of the trench to the bottom (i.e., 0.3 μm) of the trench. Mixed-type dislocation constituted about 80% of the total dislocations in the GaN grown on the inclined Si(111) surface etched on Si(100)

  17. Rhizosphere priming effects in two contrasting soils

    NASA Astrophysics Data System (ADS)

    Lloyd, Davidson; Kirk, Guy; Ritz, Karl

    2015-04-01

    Inputs of fresh plant-derived carbon may stimulate the turnover of existing soil organic matter by so-called priming effects. Priming may occur directly, as a result of nutrient 'mining' by existing microbial communities, or indirectly via population adjustments. However the mechanisms are poorly understood. We planted C4 Kikuyu grass (Pennisetum clandestinum) in pots with two contrasting C3 soils (clayey, fertile TB and sandy, acid SH), and followed the soil CO2 efflux and its δ13C. The extent of C deposition in the rhizosphere was altered by intermittently clipping the grass in half the pots; there were also unplanted controls. At intervals, pots were destructively sampled for root and shoot biomass. Total soil CO2 efflux was measured using a gas-tight PVC chamber fitted over bare soil, and connected to an infra-red gas analyser; the δ13C of efflux was measured in air sub-samples withdrawn by syringe. The extent of priming was inferred from the δ13C of efflux and the δ13C of the plant and soil end-members. In unclipped treatments, in both soils, increased total soil respiration and rhizosphere priming effects (RPE) were apparent compared to the unplanted controls. The TB soil had greater RPE overall. The total respiration in clipped TB soil was significantly greater than in the unplanted controls, but in the clipped SH soil it was not significantly different from the controls. Clipping affected plant C partitioning with greater allocation to shoot regrowth from about 4 weeks after planting. Total plant biomass decreased in the order TB unclipped > SH unclipped >TB clipped > SH clipped. The results are consistent with priming driven by microbial activation stimulated by rhizodeposits and by nitrogen demand from the growing plants under N limited conditions. Our data suggest that photosynthesis drives RPE and soil differences may alter the rate and intensity of RPE but not the direction.

  18. GaN Initiative for Grid Applications (GIGA)

    SciTech Connect

    Turner, George

    2015-07-03

    For nearly 4 ½ years, MIT Lincoln Laboratory (MIT/LL) led a very successful, DoE-funded team effort to develop GaN-on-Si materials and devices, targeting high-voltage (>1 kV), high-power, cost-effective electronics for grid applications. This effort, called the GaN Initiative for Grid Applications (GIGA) program, was initially made up of MIT/LL, the MIT campus group of Prof. Tomas Palacios (MIT), and the industrial partner M/A Com Technology Solutions (MTS). Later in the program a 4th team member was added (IQE MA) to provide commercial-scale GaN-on-Si epitaxial materials. A basic premise of the GIGA program was that power electronics, for ubiquitous utilization -even for grid applications - should be closer in cost structure to more conventional Si-based power electronics. For a number of reasons, more established GaN-on-SiC or even SiC-based power electronics are not likely to reach theses cost structures, even in higher manufacturing volumes. An additional premise of the GIGA program was that the technical focus would be on materials and devices suitable for operating at voltages > 1 kV, even though there is also significant commercial interest in developing lower voltage (< 1 kV), cost effective GaN-on-Si devices for higher volume applications, like consumer products. Remarkable technical progress was made during the course of this program. Advances in materials included the growth of high-quality, crack-free epitaxial GaN layers on large-diameter Si substrates with thicknesses up to ~5 μm, overcoming significant challenges in lattice mismatch and thermal expansion differences between Si and GaN in the actual epitaxial growth process. Such thick epilayers are crucial for high voltage operation of lateral geometry devices such as Schottky barrier (SB) diodes and high electron mobility transistors (HEMTs). New “Normally-Off” device architectures were demonstrated – for safe operation of power electronics circuits. The trade-offs between lateral and

  19. Cross-structural priming: prepositional phrase attachment primes relative clause attachment.

    PubMed

    Loncke, Maaike; Van Laere, Sébastien M J; Desmet, Timothy

    2011-01-01

    In this paper we show that attachment height (high vs. low attachment) of a modifier to a complex noun phrase (CNP; e.g., "the servant of the actress"), can be primed between dissimilar syntactic structures. In a sentence completion experiment, we found that the attachment height of a prepositional phrase (PP) in the prime sentence primed the attachment height of a relative clause (RC) in the target sentence. This cross-structural priming effect cannot be explained in terms of the priming of specific phrase-structure rules or even sequences of specific phrase-structure rules (Scheepers, 2003), because the attachment of a PP to a CNP is generated by a different phrase-structure rule than the attachment of an RC. However, the present data suggest that the location at which the RC is attached to the CNP is mentally represented, independent of the specific phrase-structure rule that is attached, or by extension, that the abstract hierarchical configuration of the full CNP and the attached RC is represented (Desmet & Declercq, 2006). This is the first demonstration of a cross-structural priming effect that cannot be captured by phrase-structure rules.

  20. Lexical enhancement during prime-target integration: ERP evidence from matched-case identity priming.

    PubMed

    Vergara-Martínez, Marta; Gómez, Pablo; Jiménez, María; Perea, Manuel

    2015-06-01

    A number of experiments have revealed that matched-case identity PRIME-TARGET pairs are responded to faster than mismatched-case identity prime-TARGET pairs for pseudowords (e.g., JUDPE-JUDPE < judpe-JUDPE), but not for words (JUDGE-JUDGE = judge-JUDGE). These findings suggest that prime-target integration processes are enhanced when the stimuli tap onto lexical representations, overriding physical differences between the stimuli (e.g., case). To track the time course of this phenomenon, we conducted an event-related potential (ERP) masked-priming lexical decision experiment that manipulated matched versus mismatched case identity in words and pseudowords. The behavioral results replicated previous research. The ERP waves revealed that matched-case identity-priming effects were found at a very early time epoch (N/P150 effects) for words and pseudowords. Importantly, around 200 ms after target onset (N250), these differences disappeared for words but not for pseudowords. These findings suggest that different-case word forms (lower- and uppercase) tap into the same abstract representation, leading to prime-target integration very early in processing. In contrast, different-case pseudoword forms are processed as two different representations. This word-pseudoword dissociation has important implications for neural accounts of visual-word recognition.

  1. It takes time to prime: semantic priming in the ocular lexical decision task.

    PubMed

    Hoedemaker, Renske S; Gordon, Peter C

    2014-12-01

    Two eye-tracking experiments were conducted in which the manual response mode typically used in lexical decision tasks (LDTs) was replaced with an eye-movement response through a sequence of 3 words. This ocular LDT combines the explicit control of task goals found in LDTs with the highly practiced ocular response used in reading text. In Experiment 1, forward saccades indicated an affirmative lexical decision (LD) on each word in the triplet. In Experiment 2, LD responses were delayed until all 3 letter strings had been read. The goal of the study was to evaluate the contribution of task goals and response mode to semantic priming. Semantic priming is very robust in tasks that involve recognition of words in isolation, such as LDT, but limited during text reading, as measured using eye movements. Gaze durations in both experiments showed robust semantic priming even though ocular response times were much shorter than manual LDs for the same words in the English Lexicon Project. Ex-Gaussian distribution fits revealed that the priming effect was concentrated in estimates of tau (τ), meaning that priming was most pronounced in the slow tail of the distribution. This pattern shows differential use of the prime information, which may be more heavily recruited in cases in which the LD is difficult, as indicated by longer response times. Compared with the manual LD responses, ocular LDs provide a more sensitive measure of this task-related influence on word recognition as measured by the LDT.

  2. Alcohol Expectancy Priming and Drinking Behavior: The Role of Compatibility between Prime and Expectancy Content

    PubMed Central

    Friedman, Ronald S.; McCarthy, Denis M.; Pedersen, Sarah L.; Hicks, Joshua A.

    2009-01-01

    According to information-processing models of alcohol use, alcohol expectancies constitute representations in long-term memorythat may be activated in the presence of drinking-related cues, thereby influencing alcohol consumption. A fundamental implication of this approach is that primed expectancies should affect drinking only for those individuals who possess the specific expectancies primed. To test this notion, in the present study, participants were initially assessed on three distinct domains of positive alcohol expectancies. Approximately one week later, they completed an ad libitum drinking study during which only a single expectancy domain (sociability) was primed in the experimental condition. Consistent with predictions, following exposure to sociability primes, but not control primes, individuals with stronger expectancies that alcohol would enhance sociability uniquely showed increased placebo consumption of nonalcoholic beer. These results, which demonstrate the moderating role of compatibility between the specific content of primes and that of underlying expectancies, offer new, direct support for memory network-based models of drinking behavior. PMID:19586149

  3. A Statistical Argument for the Weak Twin Primes Conjecture

    ERIC Educational Resources Information Center

    Bruckman, P. S.

    2006-01-01

    Certain definitions introduce appropriate concepts, among which are the definitions of the counting functions of the primes and twin primes, along with definitions of the correlation coefficient in a bivariate sample space. It is argued conjecturally that the characteristic functions of the prime "p" and of the quantity "p"+2 are highly…

  4. Going back to Donald: how comparisons shape judgmental priming effects.

    PubMed

    Mussweiler, Thomas; Damisch, Lysann

    2008-12-01

    The authors examine how judgmental priming effects are shaped by comparisons. Specifically, they suggest that concept priming involves spontaneous activation of concept-consistent standards, which are then spontaneously compared to the judgmental target. In 6 studies, they used a variety of priming methods (contextual cue, subliminal priming, indirect priming) to test these notions of spontaneous standard activation and spontaneous comparison. Study 1 demonstrates that priming a trait concept activates concept-consistent standards. Study 2 suggests that these activated standards contribute to priming effects. If alternative standards that are not particularly consistent with the primed concept are activated, priming effects diminish. Studies 3-6 show that the magnitude and direction of priming effects depend on the intensity and the type of the engaged comparison. Specifically, Study 3 demonstrates that the magnitude of a priming effect depends on the intensity of comparative processing. Studies 4 through 6 show that the direction of a priming effect (assimilation vs. contrast) depends on whether judges engage in a similarity or dissimilarity testing comparison mechanism--a factor which has been found to shape comparison consequences in other domains. (PsycINFO Database Record (c) 2008 APA, all rights reserved).

  5. Integrative Priming Occurs Rapidly and Uncontrollably during Lexical Processing

    ERIC Educational Resources Information Center

    Estes, Zachary; Jones, Lara L.

    2009-01-01

    Lexical priming, whereby a prime word facilitates recognition of a related target word (e.g., "nurse" [right arrrow] "doctor"), is typically attributed to association strength, semantic similarity, or compound familiarity. Here, the authors demonstrate a novel type of lexical priming that occurs among unassociated, dissimilar,…

  6. Persistent Structural Priming from Language Comprehension to Language Production

    ERIC Educational Resources Information Center

    Bock, Kathryn; Dell, Gary S.; Chang, Franklin; Onishi, Kristine H.

    2007-01-01

    To examine the relationship between syntactic processes in language comprehension and language production, we compared structural persistence from sentence primes that speakers heard to persistence from primes that speakers produced. [Bock, J. K., & Griffin, Z. M. (2000). The persistence of structural priming: transient activation or implicit…

  7. The effects of alerting signals in masked priming

    PubMed Central

    Fischer, Rico; Plessow, Franziska; Kiesel, Andrea

    2013-01-01

    Alerting signals often serve to reduce temporal uncertainty by predicting the time of stimulus onset. The resulting response time benefits have often been explained by facilitated translation of stimulus codes into response codes on the basis of established stimulus-response (S-R) links. In paradigms of masked S-R priming alerting signals also modulate response activation processes triggered by subliminally presented prime stimuli. In the present study we tested whether facilitation of visuo-motor translation processes due to alerting signals critically depends on established S-R links. Alerting signals resulted in significantly enhanced masked priming effects for masked prime stimuli that included and that did not include established S-R links (i.e., target vs. novel primes). Yet, the alerting-priming interaction was more pronounced for target than for novel primes. These results suggest that effects of alerting signals on masked priming are especially evident when S-R links between prime and target exist. At the same time, an alerting-priming interaction also for novel primes suggests that alerting signals also facilitate stimulus-response translation processes when masked prime stimuli provide action-trigger conditions in terms of programmed S-R links. PMID:23882248

  8. Structural Priming and Frequency Effects Interact in Chinese Sentence Comprehension

    PubMed Central

    Wei, Hang; Dong, Yanping; Boland, Julie E.; Yuan, Fang

    2016-01-01

    Previous research in several European languages has shown that the language processing system is sensitive to both structural frequency and structural priming effects. However, it is currently not clear whether these two types of effects interact during online sentence comprehension, especially for languages that do not have morphological markings. To explore this issue, the present study investigated the possible interplay between structural priming and frequency effects for sentences containing the Chinese ambiguous construction V NP1 de NP2 in a self-paced reading experiment. The sentences were disambiguated to either the more frequent/preferred NP structure or the less frequent VP structure. Each target sentence was preceded by a prime sentence of three possible types: NP primes, VP primes, and neutral primes. When the ambiguous construction V NP1 de NP2 was disambiguated to the dispreferred VP structure, participants experienced more processing difficulty following an NP prime relative to following a VP prime or a neutral baseline. When the ambiguity was resolved to the preferred NP structure, prime type had no effect. These results suggest that structural priming in comprehension is modulated by the baseline frequency of alternative structures, with the less frequent structure being more subject to structural priming effects. These results are discussed in the context of the error-based, implicit learning account of structural priming. PMID:26869954

  9. 48 CFR 45.501 - Prime contractor alternate locations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 48 Federal Acquisition Regulations System 1 2010-10-01 2010-10-01 false Prime contractor alternate... CONTRACT MANAGEMENT GOVERNMENT PROPERTY Support Government Property Administration 45.501 Prime contractor... administration from another contract administration office, for purposes of evaluating prime...

  10. Prospective and Retrospective Processing in Associative Mediated Priming

    ERIC Educational Resources Information Center

    Jones, Lara L.

    2012-01-01

    Mediated priming refers to the faster word recognition of a target (e.g., milk) following presentation of a prime (e.g., pasture) that is related indirectly via a connecting "mediator" (e.g., cow). Association strength may be an important factor in whether mediated priming occurs prospectively (with target activation prior to its presentation) or…

  11. Identifiable Orthographically Similar Word Primes Interfere in Visual Word Identification

    ERIC Educational Resources Information Center

    Burt, Jennifer S.

    2009-01-01

    University students participated in five experiments concerning the effects of unmasked, orthographically similar, primes on visual word recognition in the lexical decision task (LDT) and naming tasks. The modal prime-target stimulus onset asynchrony (SOA) was 350 ms. When primes were words that were orthographic neighbors of the targets, and…

  12. Do Stimulus-Action Associations Contribute to Repetition Priming?

    ERIC Educational Resources Information Center

    Dennis, Ian; Perfect, Timothy J.

    2013-01-01

    Despite evidence that response learning makes a major contribution to repetition priming, the involvement of response representations at the level of motor actions remains uncertain. Levels of response representation were investigated in 4 experiments that used different tasks at priming and test. Priming for stimuli that required congruent…

  13. Novel Word Lexicalization and the Prime Lexicality Effect

    ERIC Educational Resources Information Center

    Qiao, Xiaomei; Forster, Kenneth I.

    2013-01-01

    This study investigates how newly learned words are integrated into the first-language lexicon using masked priming. Two lexical decision experiments are reported, with the aim of establishing whether newly learned words behave like real words in a masked form priming experiment. If they do, they should show a prime lexicality effect (PLE), in…

  14. The Role of Polysemy in Masked Semantic and Translation Priming

    ERIC Educational Resources Information Center

    Finkbeiner, Matthew; Forster, Kenneth; Nicol, Janet; Nakamura, Kumiko

    2004-01-01

    A well-known asymmetry exists in the bilingual masked priming literature in which lexical decision is used: namely, masked primes in the dominant language (L1) facilitate decision times on targets in the less dominant language (L2), but not vice versa. In semantic categorization, on the other hand, priming is symmetrical. In Experiments 1-3 we…

  15. Cognitive Conflict and Inhibition in Primed Dichotic Listening

    ERIC Educational Resources Information Center

    Saetrevik, Bjorn; Specht, Karsten

    2009-01-01

    In previous behavioral studies, a prime syllable was presented just prior to a dichotic syllable pair, with instructions to ignore the prime and report one syllable from the dichotic pair. When the prime matched one of the syllables in the dichotic pair, response selection was biased towards selecting the unprimed target. The suggested mechanism…

  16. Give and Take: Syntactic Priming during Spoken Language Comprehension

    ERIC Educational Resources Information Center

    Thothathiri, Malathi; Snedeker, Jesse

    2008-01-01

    Syntactic priming during language production is pervasive and well-studied. Hearing, reading, speaking or writing a sentence with a given structure increases the probability of subsequently producing the same structure, regardless of whether the prime and target share lexical content. In contrast, syntactic priming during comprehension has proven…

  17. Masked Translation Priming with Semantic Categorization: Testing the Sense Model

    ERIC Educational Resources Information Center

    Wang, Xin; Forster, Kenneth I.

    2010-01-01

    Four experiments are reported which were designed to test hypotheses concerning the asymmetry of masked translation priming. Experiment 1 confirmed the presence of L2-L1 priming with a semantic categorization task and demonstrated that this effect was restricted to exemplars. Experiment 2 showed that the translation priming effect was not due to…

  18. Being Forward Not Backward: Lexical Limits to Masked Priming

    ERIC Educational Resources Information Center

    Davis, Chris; Kim, Jeesun; Forster, Kenneth I.

    2008-01-01

    This study investigated whether masked priming is mediated by existing memory representations by determining whether nonwords targets would show repetition priming. To avoid the potential confound that nonword repetition priming would be obscured by a familiarity response bias, the standard lexical decision and naming tasks were modified to make…

  19. Electrophysiological and Behavioral Evidence of Syntactic Priming in Sentence Comprehension

    ERIC Educational Resources Information Center

    Tooley, Kristen M.; Traxler, Matthew J.; Swaab, Tamara Y.

    2009-01-01

    Event-related potentials and eye tracking were used to investigate the nature of priming effects in sentence comprehension. Participants read 2 sentences (a prime sentence and a target sentence), both of which had a difficult and ambiguous sentence structure. The prime and target sentences contained either the same verb or verbs that were very…

  20. 7 CFR 29.1166 - Primings (P Group).

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    .... Grades, Grade Names, Minimum Specifications, and Tolerances P2L—Fine Quality Lemon Primings Prematurely... tolerance 25 percent, of which not over 10 percent may be waste. P3L—Good Quality Lemon Primings Prematurely... tolerance 40 percent, of which not over 20 percent may be waste. P4L—Fair Quality Lemon Primings...

  1. 7 CFR 29.1166 - Primings (P Group).

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    .... Grades, Grade Names, Minimum Specifications, and Tolerances P2L—Fine Quality Lemon Primings Prematurely... tolerance 25 percent, of which not over 10 percent may be waste. P3L—Good Quality Lemon Primings Prematurely... tolerance 40 percent, of which not over 20 percent may be waste. P4L—Fair Quality Lemon Primings...

  2. 7 CFR 29.1166 - Primings (P Group).

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    .... Grades, Grade Names, Minimum Specifications, and Tolerances P2L—Fine Quality Lemon Primings Prematurely... tolerance 25 percent, of which not over 10 percent may be waste. P3L—Good Quality Lemon Primings Prematurely... tolerance 40 percent, of which not over 20 percent may be waste. P4L—Fair Quality Lemon Primings...

  3. 7 CFR 29.1166 - Primings (P Group).

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    .... Grades, Grade Names, Minimum Specifications, and Tolerances P2L—Fine Quality Lemon Primings Prematurely... tolerance 25 percent, of which not over 10 percent may be waste. P3L—Good Quality Lemon Primings Prematurely... tolerance 40 percent, of which not over 20 percent may be waste. P4L—Fair Quality Lemon Primings...

  4. Nearly 4-Inch-Diameter Free-Standing GaN Wafer Fabricated by Hydride Vapor Phase Epitaxy with Pit-Inducing Buffer Layer

    NASA Astrophysics Data System (ADS)

    Sato, Tadashige; Okano, Shinya; Goto, Takenari; Yao, Takafumi; Seto, Ritsu; Sato, Akira; Goto, Hideki

    2013-08-01

    A free-standing GaN wafer was fabricated by depositing a GaN buffer that induced the formation of pits (hereafter, pit-inducing GaN buffer) on a low-temperature-grown GaN buffer on the sapphire substrate. A high-temperature-grown GaN layer was grown on the pit-inducing GaN buffer that induced the formation of pits on the high-temperature-grown GaN layer. The pit-inducing buffer suppresses crack formation in the thick GaN film thereby releasing growth stress. Thermal stress in GaN on a sapphire system is also discussed on the basis of calculations utilizing a bilayer model. We have succeeded in the fabrication of a nearly 4-in.-diameter free-standing GaN thick wafer with a pit-inducing GaN buffer by one-stop hydride vapor phase epitaxy, which will lead to a low-cost fabrication of free-standing GaN wafers.

  5. The temporal dynamics of masked repetition picture priming effects: manipulations of stimulus-onset asynchrony (SOA) and prime duration.

    PubMed

    Eddy, Marianna D; Holcomb, Phillip J

    2010-06-22

    The current study used event-related potentials (ERPs) and masked repetition priming to examine the time-course of picture processing. We manipulated the stimulus-onset asynchrony (110 ms, 230 ms, 350 ms, and 470 ms) between repeated and unrepeated prime-target pairs while holding the prime duration constant (50 ms) (Experiment 1) as well as the prime durations (30 ms, 50 ms, 70 ms, and 90 ms) (Experiment 2) with a constant SOA of 110 ms in a masked repetition priming paradigm with pictures. The aim of this study was to further elucidate the mechanisms underlying previously observed ERP components in masked priming with pictures. We found that both the N/P190 and N400 are modulated by changes in prime duration and SOA, however, it appears that longer prime exposure rather than a longer SOA leads to more in-depth processing as indexed by larger N400 effects.

  6. GaN Microwave DC-DC Converters

    NASA Astrophysics Data System (ADS)

    Ramos Franco, Ignacio

    Increasing the operating frequency of switching converters can have a direct impact in the miniaturization and integration of power converters. The size of energy-storage passive components and the difficulty to integrate them with the rest of the circuitry is a major challenge in the development of a fully integrated power supply on a chip. The work presented in this thesis attempts to address some of the difficulties encountered in the design of high-frequency converters by applying concepts and techniques usually used in the design of high-efficiency power amplifiers and high-efficiency rectifiers at microwave frequencies. The main focus is in the analysis, design, and characterization of dc-dc converters operating at microwave frequencies in the low gigahertz range. The concept of PA-rectifier duality, where a high-efficiency power amplifier operates as a high-efficiency rectifier is investigated through non-linear simulations and experimentally validated. Additionally, the concept of a self-synchronous rectifier, where a transistor rectifier operates synchronously without the need of a RF source or driver is demonstrated. A theoretical analysis of a class-E self-synchronous rectifier is presented and validated through non-linear simulations and experiments. Two GaN class-E2 dc-dc converters operating at a switching frequency of 1 and 1.2 GHz are demonstrated. The converters achieve 80 % and 75 % dc-dc efficiency respectively and are among the highest-frequency and highest-efficiency reported in the literature. The application of the concepts established in the analysis of a self-synchronous rectifier to a power amplifier culminated in the development of an oscillating, self-synchronous class-E 2 dc-dc converter. Finally, a proof-of-concept fully integrated GaN MMIC class-E 2 dc-dc converter switching at 4.6 GHz is demonstrated for the first time to the best of our knowledge. The 3.8 mm x 2.6 mm chip contains distributed inductors and does not require any

  7. Nanostructural engineering of nitride nucleation layers for GaN substrate dislocation reduction.

    SciTech Connect

    Koleske, Daniel David; Lee, Stephen Roger; Lemp, Thomas Kerr; Coltrin, Michael Elliott; Cross, Karen Charlene; Thaler, Gerald

    2009-07-01

    With no lattice matched substrate available, sapphire continues as the substrate of choice for GaN growth, because of its reasonable cost and the extensive prior experience using it as a substrate for GaN. Surprisingly, the high dislocation density does not appear to limit UV and blue LED light intensity. However, dislocations may limit green LED light intensity and LED lifetime, especially as LEDs are pushed to higher current density for high end solid state lighting sources. To improve the performance for these higher current density LEDs, simple growth-enabled reductions in dislocation density would be highly prized. GaN nucleation layers (NLs) are not commonly thought of as an application of nano-structural engineering; yet, these layers evolve during the growth process to produce self-assembled, nanometer-scale structures. Continued growth on these nuclei ultimately leads to a fully coalesced film, and we show in this research program that their initial density is correlated to the GaN dislocation density. In this 18 month program, we developed MOCVD growth methods to reduce GaN dislocation densities on sapphire from 5 x 10{sup 8} cm{sup -2} using our standard delay recovery growth technique to 1 x 10{sup 8} cm{sup -2} using an ultra-low nucleation density technique. For this research, we firmly established a correlation between the GaN nucleation thickness, the resulting nucleation density after annealing, and dislocation density of full GaN films grown on these nucleation layers. We developed methods to reduce the nuclei density while still maintaining the ability to fully coalesce the GaN films. Ways were sought to improve the GaN nuclei orientation by improving the sapphire surface smoothness by annealing prior to the NL growth. Methods to eliminate the formation of additional nuclei once the majority of GaN nuclei were developed using a silicon nitride treatment prior to the deposition of the nucleation layer. Nucleation layer thickness was determined

  8. Interface Electronic State Characterization of Plasma Enhanced Atomic Layer Deposited Dielectrics on GaN

    NASA Astrophysics Data System (ADS)

    Yang, Jialing

    In this dissertation, the interface chemistry and electronic structure of plasma-enhanced atomic layer deposited (PEALD) dielectrics on GaN are investigated with x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). Three interrelated issues are discussed in this study: (1) PEALD dielectric growth process optimization, (2) interface electronic structure of comparative PEALD dielectrics on GaN, and (3) interface electronic structure of PEALD dielectrics on Ga- and N-face GaN. The first study involved an in-depth case study of PEALD Al2O3 growth using dimethylaluminum isopropoxide, with a special focus on oxygen plasma effects. Saturated and self-limiting growth of Al2O3 films were obtained with an enhanced growth rate within the PEALD temperature window (25--220 °C). The properties of Al2O3 deposited at various temperatures were characterized to better understand the relation between the growth parameters and film properties. In the second study, the interface electronic structures of PEALD dielectrics on Ga-face GaN films were measured. Five promising dielectrics (Al2O3, HfO2, SiO2, La2O 3, and ZnO) with a range of band gap energies were chosen. Prior to dielectric growth, a combined wet chemical and in-situ H 2/N2 plasma clean process was employed to remove the carbon contamination and prepare the surface for dielectric deposition. The surface band bending and band offsets were measured by XPS and UPS for dielectrics on GaN. The trends of the experimental band offsets on GaN were related to the dielectric band gap energies. In addition, the experimental band offsets were near the calculated values based on the charge neutrality level model. The third study focused on the effect of the polarization bound charge of the Ga- and N-face GaN on interface electronic structures. A surface pretreatment process consisting of a NH4OH wet chemical and an in-situ NH3 plasma treatment was applied to remove carbon contamination, retain monolayer oxygen coverage, and

  9. Thermal evolution of microstructure in ion-irradiated GaN

    SciTech Connect

    Bae, In-Tae; Jiang, Weilin; Wang, Chong M.; Weber, William J.; Zhang, Yanwen

    2009-04-20

    The thermal evolution of the microstructure created by irradiation of a GaN single crystal with 2 MeV Au2+ ions at 150 K is characterized following annealing at 973 K using transmission electron microscopy. In the as-irradiated sample characterized at 300 K, Ga nanocrystals with the diamond structure, which is an unstable configuration for Ga, are directly observed together with nitrogen bubbles in the irradiation-induced amorphous layer. Upon thermal annealing, the thickness of the amorphous layer decreases by ~13.1 %, and nano-beam electron diffraction analysis indicates no evidence for residual Ga nanocrystals, but instead reveals a mixture of hexagonal and cubic GaN phases in the annealed sample. Nitrogen molecules, captured in the as-irradiated bubbles, appear to debond and react with the Ga nanocrystals during the thermal annealing to form crystalline GaN. In addition, electron energy loss spectroscopy measurements reveal an atomic volume change of 18.9 % for the as-irradiated amorphous layer relative to the virgin single crystal GaN. This relative swelling of the damaged layer reduces to 7.7 % after thermal annealing. Partial recrystallization and structural relaxation of the GaN amorphous state are believed responsible for the volume change.

  10. Ultrathin GaN quantum disk nanowire LEDs with sub-250 nm electroluminescence

    NASA Astrophysics Data System (ADS)

    Sarwar, A. T. M. Golam; May, Brelon J.; Chisholm, Matthew F.; Duscher, Gerd J.; Myers, Roberto C.

    2016-04-01

    By quantum confining GaN at monolayer thickness with AlN barriers inside of a nanowire, deep ultraviolet LEDs are demonstrated. Full three-dimensional strain dependent energy band simulations are carried out within multiple quantum disk (MQD) GaN/AlN nanowire superlattice heterostructures. It is found that, even within the same nanowire MQD, the emission energy of the ultrathin GaN QDs varies from disk to disk due to the changing strain distribution and polarization charge induced energy band bending along the axial nanowire direction. MQD heterostructures are grown by plasma-assisted molecular beam epitaxy to form self-assembled catalyst-free nanowires with 1 to 2 monolayer thick GaN insertions within an AlN matrix. Photoluminescence peaks are observed at 295 nm and 283 nm from the 2 ML and 1 ML thick MQD samples, respectively. Polarization-doped nanowire LEDs are grown incorporating 1 ML thick GaN MQD active regions from which we observe deep ultraviolet electroluminescence. The shortest LED wavelength peak observed is 240 nm and attributed to electron hole recombination within 1 ML thick GaN QDs.

  11. Transport properties, specific heat and thermal conductivity of GaN nanocrystalline ceramic

    SciTech Connect

    Sulkowski, Czeslaw; ChuchmaLa, Andrzej; Zaleski, Andrzej J.; Matusiak, Marcin; Mucha, Jan; GLuchowski, PaweL; Strek, WiesLaw

    2010-10-15

    The structural and transport properties (resistivity, thermopower and Hall effect), specific heat and thermal conductivity have been measured for GaN nanocrystalline ceramic prepared by hot pressing. It was found that the temperature dependence of resistivity in temperature range 10-300 K shows the very low activation energy, which is ascribed to the shallow donor doping originating in amorphous phase of sample. The major charge carriers are electrons, what is indicated by negative sign of Hall constant and Seebeck coefficient. The thermopower attains large values (-58 {mu}V/K at 300 K) and was characterized by linear temperature dependence which suggests the diffusion as a major contribution to Seebeck effect. The high electron concentration of 1.3x10{sup 19} cm{sup -3} and high electronic specific heat coefficient determined to be 2.4 mJ/molK{sup 2} allow to conclude that GaN ceramic demonstrates the semimetallic-like behavior accompanied by very small mobility of electrons ({approx}0.1 cm{sup 2}/V s) which is responsible for its high resistivity. A low heat conductivity of GaN ceramics is associated with partial amorphous phase of GaN grains due to high pressure sintering. - Graphical Abstract: Thermal resistivity and thermopower measurements indicates the high phonon scattering and lack of phonon-drag contribution to thermopower in GaN nanoceramics pressed under 4 GPa at 800 {sup o}C.

  12. Electron spin relaxation in two polymorphic structures of GaN

    NASA Astrophysics Data System (ADS)

    Kang, Nam Lyong

    2015-03-01

    The relaxation process of electron spin in systems of electrons interacting with piezoelectric deformation phonons that are mediated through spin-orbit interactions was interpreted from a microscopic point of view using the formula for the electron spin relaxation times derived by a projection-reduction method. The electron spin relaxation times in two polymorphic structures of GaN were calculated. The piezoelectric material constant for the wurtzite structure obtained by a comparison with a previously reported experimental result was {{P}pe}=1.5 × {{10}29} eV {{m}-1}. The temperature and magnetic field dependence of the relaxation times for both wurtzite and zinc-blende structures were similar, but the relaxation times in zinc-blende GaN were smaller and decreased more rapidly with increasing temperature and magnetic field than that in wurtzite GaN. This study also showed that the electron spin relaxation for wurtzite GaN at low density could be explained by the Elliot-Yafet process but not for zinc-blende GaN in the metallic regime.

  13. Spontaneously grown GaN and AlGaN nanowires

    NASA Astrophysics Data System (ADS)

    Bertness, K. A.; Roshko, A.; Sanford, N. A.; Barker, J. M.; Davydov, A. V.

    2006-01-01

    We have identified crystal growth conditions in gas-source molecular beam epitaxy (MBE) that lead to spontaneous formation of GaN nanowires with high aspect ratio on Si (1 1 1) substrates. The nanowires were oriented along the GaN c-axis and normal to the substrate surface. Unlike in many other reports of GaN nanowire growth, no metal catalysts were used. Low growth rates at substrate temperatures near 820 °C were combined with high nitrogen flux (partially dissociated with RF plasma excitation) to form well-separated GaN wires with diameters from 50 to 250 nm in diameter and lengths ranging from 2 to 7 μm. The nanowires grew out of an irregular matrix layer containing deep faceted holes. X-ray diffraction indicated that the wires were fully relaxed and aligned to the silicon substrate. The growth morphology was strongly affected by the presence of Al and Be. The changes suggest that surface diffusion is a primary driving force in the growth of GaN nanowires with MBE.

  14. Ultrathin GaN quantum disk nanowire LEDs with sub-250 nm electroluminescence

    SciTech Connect

    Chisholm, Matthew F.; Golam Sarwar, A. T. M.; Myers, Roberto C.; Mays, Brelon J.; Duscher, Gerd J.

    2016-03-18

    By quantum confining GaN at monolayer thickness with AlN barriers inside of a nanowire, deep ultraviolet LEDs are demonstrated. Full three-dimensional strain dependent energy band simulations are carried out within multiple quantum disk (MQD) GaN/AlN nanowire superlattice heterostructures. It is found that, even within the same nanowire MQD, the emission energy of the ultrathin GaN QDs varies from disk to disk due to the changing strain distribution and polarization charge induced energy band bending along the axial nanowire direction. MQD heterostructures are grown by plasma-assisted molecular beam epitaxy to form self-assembled catalyst-free nanowires with 1 to 2 monolayer thick GaN insertions within an AlN matrix. Photoluminescence peaks are observed at 295 nm and 283 nm from the 2 ML and 1 ML thick MQD samples, respectively. Polarization-doped nanowire LEDs are grown incorporating 1 ML thick GaN MQD active regions from which we observe deep ultraviolet electroluminescence. As a result, the shortest LED wavelength peak observed is 240 nm and attributed to electron hole recombination within 1 ML thick GaN QDs.

  15. Improved crystalline quality of N-polar GaN epitaxial layers grown with reformed flow-rate-modulation technology

    NASA Astrophysics Data System (ADS)

    Zhang, Heng; Zhang, Xiong; Wang, Shuchang; Wang, Xiaolei; Zhao, Jianguo; Wu, Zili; Dai, Qian; Yang, Hongquan; Cui, Yiping

    2017-01-01

    A reformed flow-rate-modulation technology was developed for the metalorganic vapor phase epitaxy (MOVPE) growth of the N-polar GaN epitaxial layers. To improve the crystalline quality of the N-polar GaN epitaxial layers, a GaN nucleation layer was grown at relatively low temperature with carefully-controlled pulsed supply of Ga source and showed diverse morphology with atomic force microscope (AFM). Furthermore, the electrical and optical properties of the grown N-polar GaN epitaxial layers were investigated extensively by means of Hall effect, photoluminescence (PL), and X-ray rocking curve (XRC) measurements. The characterization results revealed that as compared with the N-polar GaN epitaxial layer grown over the conventional GaN nucleation layer which was deposited with continuous supply of both N and Ga sources, the electrical and optical properties of the N-polar GaN epitaxial layer grown with optimized supply of Ga source for the GaN nucleation layer were significantly improved.

  16. One-step fabrication of porous GaN crystal membrane and its application in energy storage

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Wang, Shouzhi; Shao, Yongliang; Wu, Yongzhong; Sun, Changlong; Huo, Qin; Zhang, Baoguo; Hu, Haixiao; Hao, Xiaopeng

    2017-03-01

    Single-crystal gallium nitride (GaN) membranes have great potential for a variety of applications. However, fabrication of single-crystalline GaN membranes remains a challenge owing to its chemical inertness and mechanical hardness. This study prepares large-area, free-standing, and single-crystalline porous GaN membranes using a one-step high-temperature annealing technique for the first time. A promising separation model is proposed through a comprehensive study that combines thermodynamic theories analysis and experiments. Porous GaN crystal membrane is processed into supercapacitors, which exhibit stable cycling life, high-rate capability, and ultrahigh power density, to complete proof-of-concept demonstration of new energy storage application. Our results contribute to the study of GaN crystal membranes into a new stage related to the elelctrochemical energy storage application.

  17. One-step fabrication of porous GaN crystal membrane and its application in energy storage

    PubMed Central

    Zhang, Lei; Wang, Shouzhi; Shao, Yongliang; Wu, Yongzhong; Sun, Changlong; Huo, Qin; Zhang, Baoguo; Hu, Haixiao; Hao, Xiaopeng

    2017-01-01

    Single-crystal gallium nitride (GaN) membranes have great potential for a variety of applications. However, fabrication of single-crystalline GaN membranes remains a challenge owing to its chemical inertness and mechanical hardness. This study prepares large-area, free-standing, and single-crystalline porous GaN membranes using a one-step high-temperature annealing technique for the first time. A promising separation model is proposed through a comprehensive study that combines thermodynamic theories analysis and experiments. Porous GaN crystal membrane is processed into supercapacitors, which exhibit stable cycling life, high-rate capability, and ultrahigh power density, to complete proof-of-concept demonstration of new energy storage application. Our results contribute to the study of GaN crystal membranes into a new stage related to the elelctrochemical energy storage application. PMID:28281562

  18. One-step fabrication of porous GaN crystal membrane and its application in energy storage.

    PubMed

    Zhang, Lei; Wang, Shouzhi; Shao, Yongliang; Wu, Yongzhong; Sun, Changlong; Huo, Qin; Zhang, Baoguo; Hu, Haixiao; Hao, Xiaopeng

    2017-03-10

    Single-crystal gallium nitride (GaN) membranes have great potential for a variety of applications. However, fabrication of single-crystalline GaN membranes remains a challenge owing to its chemical inertness and mechanical hardness. This study prepares large-area, free-standing, and single-crystalline porous GaN membranes using a one-step high-temperature annealing technique for the first time. A promising separation model is proposed through a comprehensive study that combines thermodynamic theories analysis and experiments. Porous GaN crystal membrane is processed into supercapacitors, which exhibit stable cycling life, high-rate capability, and ultrahigh power density, to complete proof-of-concept demonstration of new energy storage application. Our results contribute to the study of GaN crystal membranes into a new stage related to the elelctrochemical energy storage application.

  19. A New Method to Modify Two-Dimensional Electron Gas Density by GaN Cap Etching

    NASA Astrophysics Data System (ADS)

    Li, Zhongda; Chow, T. Paul

    2013-08-01

    We have experimentally demonstrated a new method for modifying the two-dimensional electron density (2DEG) at the AlGaN/GaN interface by etching of the GaN cap layer on top of the AlGaN. GaN MOS capacitors have been fabricated on samples with partially or fully etched GaN cap, and the 2DEG density has been extracted. The results show a linear relation between the 2DEG density and the thickness of the GaN cap being etched. We have also fabricated van der Pauw structures and obtained the 2DEG density using Hall measurements, and the results are consistent with that from the GaN MOS capacitors.

  20. Synthesis of GaN nanowires on gold-coated SiC substrates by novel pulsed electron deposition technique

    NASA Astrophysics Data System (ADS)

    Lei, M.; Yang, H.; Li, P. G.; Tang, W. H.

    2008-01-01

    A two-step approach for macro-synthesis of GaN nanowires was developed in this study. GaN nanoparticles were firstly synthesized through a facile solid-state reaction using an organic reagent dicyandiamide (C 2N 4H 4) and Ga 2O 3 as precursors. Subsequently, single-crystalline wurtzite GaN nanowires were grown on gold-coated 6H-SiC substrates via novel pulsed electron deposition (PED) technique using the as-prepared GaN nanoparticles as target, which provides a new route employing nanoparticles as precursors to fabricate GaN nanowires. It is found that pulsed electron ablation induced Ga and N plasma directly towards the gold-coated substrate to initialize the vapor-liquid-solid (VLS) growth processes. The morphological and structural properties were investigated in detail and Raman scattering spectrum of these nanowires presented some new features.

  1. The depth-profiled carrier concentration and scattering mechanism in undoped GaN film grown on sapphire

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Chen, X. D.; Fung, S.; Beling, C. D.; Ling, C. C.; Wei, Z. F.; Xu, S. J.; Zhi, C. Y.

    2004-07-01

    Temperature-dependent Hall (TDH) measurements and confocal micro-Raman spectroscopy have been used to study the free carrier spatial distribution and scattering mechanism in unintentionally doped GaN film grown on the sapphire substrate with the method of metalorganic chemical vapor deposition. Both the TDH data and the depth-profiled Raman spectra agreed with the existence of a nonuniform spatial distribution of free carriers in the GaN film with a highly conductive layer of ˜1 μm thickness near the GaN sapphire boundary. With the consideration of this parallel conduction channel adjacent to GaN sapphire boundary, detailed analysis of the TDH mobility data suggests that a relatively high concentration of nitrogen vacancies exists and nitrogen vacancy scattering has an important influence on limiting the electron mobility in the bulk film of the present GaN sample.

  2. Preparation of Freestanding GaN Wafers by Hydride Vapor Phase Epitaxy with Void-Assisted Separation

    NASA Astrophysics Data System (ADS)

    Oshima, Yuichi; Eri, Takeshi; Shibata, Masatomo; Sunakawa, Haruo; Kobayashi, Kenji; Ichihashi, Toshinari; Usui, Akira

    2003-01-01

    We have developed a novel technique for preparing large-scale freestanding GaN wafers. Hydride vapor phase epitaxy (HVPE) growth of thick GaN layer was performed on a GaN template with a thin TiN film on the top. After the cooling process of the HVPE growth, the thick GaN layer was easily separated from the template by the assistance of many voids generated around the TiN film. As a result, a freestanding GaN wafer was obtained. The wafer obtained had a diameter of 45 mm, and a mirror-like surface. The-full-width-at-half-maximum (FWHM) of (0002) and (10\\bar{1}0) peaks in the X-ray rocking curve profile were 60 and 92 arcsec, respectively. The dislocation density was evaluated at 5× 106 cm-3 by etch pit density measurement.

  3. AMIE Gan Island Ancillary Disdrometer Field Campaign Report

    SciTech Connect

    Oue, Mariko

    2016-04-01

    As part of the U.S. Department of Energy (DOE)’s Atmospheric Radiation Measurement Climate Research Facility (ARM) Madden-Julian Oscillation (MJO) Investigation Experiment (AMIE), in January 2012 a disdrometer observation took place with the second ARM Mobile Facility (AMF2), the Scanning ARM Cloud Radar (SACR), the Texas A&M SMART-R C-band radar, and the National Center for Atmospheric Research (NCAR) dual wavelength S- and Ka-bands polarimetric (SPolKa) radar on Gan Island, Maldives. In order to measure raindrop size distributions, a disdrometer of Nagoya University, Japan, was set up close to the ARM Two-Dimensional (2D) Video Disdrometer (2DVD). The SMART-R and SPolKa radars performed range-height-indicator scanning in the direction of the disdrometer site. Comparing the disdrometer data with 2DVD data, the raindrop size distribution data will be calibrated. Furthermore, the analysis of the raindrop size distribution and radar data will be expected to clarify the microphysics in tropical convective clouds.

  4. Vertical Graphene-base transistor on GaN substrate

    NASA Astrophysics Data System (ADS)

    Zubair, Ahmad; Saadat, Omair; Song, Yi; Kong, Jing; Dresselhaus, Mildred; Palacios, Tomas

    2014-03-01

    The high carrier mobility, saturation velocity and thermal conductivity make graphene an attractive candidate for RF electronics. In addition to conventional lateral transistors, several alternative vertical device structures like hot electron transistors have been demonstrated to be promising for RF applications. The unique combination of sub-nanometer thickness and high conductivity makes graphene an excellent base material for hot electron transistors by lowering the base transit time in these vertical devices. The demonstrated graphene-base hot electron transistor performance is limited by low current density and low common-base current gain. In this work, we fabricated a graphene-base transistor on GaN/AlGaN heterostructure. We studied the tunneling from GaN/AlGaN heterojunction to graphene and compared with other demonstrated vertical graphene-base devices. We also investigated the effect of AlGaN thickness and different filtering barriers on both room temperature and low temperature transport characteristics of the fabricated devices. With careful design and optimization of the structure, graphene-base transistors on GaN substrate can be a potential candidate for future graphene RF electronics.

  5. Radiation Characterization of Commercial GaN Devices

    NASA Technical Reports Server (NTRS)

    Harris, Richard D.; Scheick, Leif Z.; Hoffman, James P.; Thrivikraman, Tushar; Jenabi, Masud; Gim, Yonggyu; Miyahira, Tetsuo

    2011-01-01

    Radiative feedback from primordial protostars and final mass of the first star Commercially available devices fabricated from GaN are beginning to appear from a number of different suppliers. Based on previous materials and prototype device studies, it is expected that these commercial devices will be quite tolerant to the types of radiation encountered in space. This expectation needs to be verified and the study described herein was undertaken for that purpose. All of the parts discussed in this report are readily available commercially. The parts chosen for study are all targeted for RF applications. Three different studies were performed: 1) a preliminary DDD/TID test of a variety of part types was performed by irradiating with 50 MeV protons, 2) a detailed DDD/TID study of one particular part type was performed by irradiating with 50 MeV protons, and 3) a SEB/SEGR test was performed on a variety of part types by irradiating with heavy ions. No significant degradation was observed in the tests performed in this study.

  6. Optical Properties of GaN and ZnO

    NASA Astrophysics Data System (ADS)

    Song, J.-H.

    A brief review on the optical properties of wurtzite ZnO and GaN is presented in this chapter with an emphasis on comparison between the materials. The properties of free excitons and impurity-bound excitons, such as their energetic positions and binding energies, are summarized. The localization energy and the ionization energy of the dominant impurities obtained by emission spectroscopy are also presented. Typical aspects of emissions from donor—acceptor pairs, free-to-bound transition, and deep level recombination are discussed. Several experimental characteristics of the relevant heterostructures, InGaN/GaN and MgZnO/ZnO, are also given below. Basic optical methods characterizing the effects of internal electric fields and carrier-localization are summarized. The unique properties of polarization sensitive emissions from nonpolar films are presented. Based on the valence band structures, the polarization selection rules can be obtained in simpler forms. Some recent reports will also be introduced stating that the anisotropic strain in nonpolar films plays an important role in deciding the polarization selectivity. The results of Raman spectroscopy are summarized in the end, with the emphasis on deciding the residual strain and the carrier concentration.

  7. Repetition priming results in sensitivity attenuation

    PubMed Central

    Allenmark, Fredrik; Hsu, Yi-Fang; Roussel, Cedric; Waszak, Florian

    2015-01-01

    Repetition priming refers to the change in the ability to perform a task on a stimulus as a consequence of a former encounter with that very same item. Usually, repetition results in faster and more accurate performance. In the present study, we used a contrast discrimination protocol to assess perceptual sensitivity and response bias of Gabor gratings that are either repeated (same orientation) or alternated (different orientation). We observed that contrast discrimination performance is worse, not better, for repeated than for alternated stimuli. In a second experiment, we varied the probability of stimulus repetition, thus testing whether the repetition effect is due to bottom-up or top-down factors. We found that it is top-down expectation that determines the effect. We discuss the implication of these findings for repetition priming and related phenomena as sensory attenuation. This article is part of a Special Issue entitled SI: Prediction and Attention. PMID:25819554

  8. The Original Gemini 9 Prime Crew

    NASA Technical Reports Server (NTRS)

    1966-01-01

    The original Gemini 9 prime crew, astronauts Elliot M. See Jr. (left), command pilot, and Charles A. Bassett II, pilot, in space suits with their helmets on the table in front of them. On February 28, 1966 the prime crew for the Gemini 9 mission were killed when their twin seat T-38 trainer jet aircraft crashed into a building in which the Gemini spacecraft were being manufactured. They were on final approach to Lambert-Saint Louis Municipal Airport when bad weather conditions hampered pilot See's ability to make a good visual contact with the runway. Noticing the building at the last second as he came out of the low cloud cover, See went to full afterburner and attempted to nose-up the aircraft in an attempt to miss the building. He clipped it and his plane crashed.

  9. Average prime-pair counting formula

    NASA Astrophysics Data System (ADS)

    Korevaar, Jaap; Riele, Herman Te

    2010-04-01

    Taking r>0 , let π_{2r}(x) denote the number of prime pairs (p, p+2r) with p≤ x . The prime-pair conjecture of Hardy and Littlewood (1923) asserts that π_{2r}(x)˜ 2C_{2r} {li}_2(x) with an explicit constant C_{2r}>0 . There seems to be no good conjecture for the remainders ω_{2r}(x)=π_{2r}(x)- 2C_{2r} {li}_2(x) that corresponds to Riemann's formula for π(x)-{li}(x) . However, there is a heuristic approximate formula for averages of the remainders ω_{2r}(x) which is supported by numerical results.

  10. [A brief textual research on circulated versions of Dan tai yu an (Jade Case Records of Red Stage].

    PubMed

    Xu, Gao; Zhu, Jianping

    2014-03-01

    Dan tai yu an (Jade Case Records of Red Stage) was compiled by a doctor of the Ming Dynasty Sun Wenyin, including 6 volumes. This book involves Chinese internal medicine, paediatrics, gynaecology, external medicine, and Department of the sense organs (ENT) classified into 73 categories, each of which contains 80 kinds of disease. The total number of disease was 157. Each kind of disease is discussed under the order of etiology, syndrome, pulse condition and treatment. The range of traditional Chinese prescriptions in this book is rather extensive with its indications, administrations and modification of main prescriptions given concretely. Both internal and external treatment are included, and the individual drug and proved recipe are practical and effective, which is a significant reference to clinical practice. There are many versions of this book extant. According to our investigation and research, we replenished some information to the"General Catalogue of TCM Ancient Books", and at the same time, correct some mistakes, providing the basis for further collation and publishing.

  11. Spin-polarized currents and noise in normal-metal/superconductor junctions with Yu-Shiba-Rusinov impurities

    NASA Astrophysics Data System (ADS)

    Persson, Daniel; Shevtsov, Oleksii; Löfwander, Tomas; Fogelström, Mikael

    2016-10-01

    Conventional superconductors disordered by magnetic impurities demonstrate physical properties that are drastically different from their pristine counterparts. In our previous work [D. Persson et al., Phys. Rev. B 92, 245430 (2015), 10.1103/PhysRevB.92.245430], we explored the spectral and thermodynamic properties of such systems for two extreme cases: completely random and ferromagnetically aligned impurity magnetic moments. Here we consider the transport properties of these systems and show that they have a potential to be used in superconducting spintronic devices. Each magnetic impurity contributes a Yu-Shiba-Rusinov (YSR) bound state to the spectrum, residing at subgap energies. Provided the YSR states form metallic bands, we demonstrate that the tunneling current carried by these states can be highly spin polarized when the impurities are ferromagnetically ordered. The spin polarization can be switched by tuning the bias voltage. Moreover, even when the impurity spins are completely uncorrelated, one can still achieve almost 100 % spin polarization of the current, if the tunnel interface is spin active. We compute electric current and noise, varying parameters of the interface between tunneling and fully transparent regimes, and analyze the relative role of single-particle and Andreev reflection processes.

  12. Ancient Chinese Formula Qiong-Yu-Gao Protects Against Cisplatin-Induced Nephrotoxicity Without Reducing Anti-tumor Activity.

    PubMed

    Teng, Zhi-Ying; Cheng, Xiao-Lan; Cai, Xue-Ting; Yang, Yang; Sun, Xiao-Yan; Xu, Jin-Di; Lu, Wu-Guang; Chen, Jiao; Hu, Chun-Ping; Zhou, Qian; Wang, Xiao-Ning; Li, Song-Lin; Cao, Peng

    2015-10-29

    Cisplatin is a highly effective anti-cancer chemotherapeutic agent; however, its clinical use is severely limited by serious side effects, of which nephrotoxicity is the most important. In this study, we investigated whether Qiong-Yu-Gao (QYG), a popular traditional Chinese medicinal formula described 840 years ago, exhibits protective effects against cisplatin-induced renal toxicity. Using a mouse model of cisplatin-induced renal dysfunction, we observed that pretreatment with QYG attenuated cisplatin-induced elevations in blood urea nitrogen and creatinine levels, ameliorated renal tubular lesions, reduced apoptosis, and accelerated tubular cell regeneration. Cisplatin-mediated elevations in tumor necrosis factor alpha (TNF-α) mRNA, interleukin-1 beta (IL-1β) mRNA, and cyclooxygenase-2 (COX-2) protein in the kidney were also significantly suppressed by QYG treatment. Furthermore, QYG reduced platinum accumulation in the kidney by decreasing the expression of copper transporter 1 and organic cation transporter 2. An in vivo study using implanted Lewis lung cancer cells revealed that concurrent administration of QYG and cisplatin did not alter the anti-tumor activity of cisplatin. Our findings suggest that the traditional Chinese medicinal formula QYG inhibits cisplatin toxicity by several mechanisms that act simultaneously, without compromising its therapeutic efficacy. Therefore, QYG may be useful in the clinic as a protective agent to prevent cisplatin-induced nephrotoxicity.

  13. The frequency attenuation effect in identity and associative priming.

    PubMed

    Nievas, Francisco

    2010-05-01

    Three lexical decision experiments were carried out, where the masked priming paradigm is used to study the role of the frequency attenuation effect (more priming in low-frequency target words than in high-frequency target words) in repetition and associative priming, manipulating Prime Duration (PD) and Stimulus Onset Asynchrony (SOA). A new concept was introduced, Minimum Time Threshold (MTT), this is, the minimum time interval of exposure to the masked word in order to become aware of it. Results support the notion that MTT is a key to the appearance of the frequency attenuation effect when enough word processing time is allowed. Results do not support the unified explanation of masked priming and long-term priming as proposed by Bodner and Masson (2001). Moreover, information feedback from the semantic level was not the reason for the frequency attenuation effect in repetition priming.

  14. Intact Conceptual Priming in the Absence of Declarative Memory

    PubMed Central

    Levy, D.A.; Stark, C.E.L.; Squire, L.R.

    2009-01-01

    Priming is an unconscious (nondeclarative) form of memory whereby identification or production of an item is improved by an earlier encounter. It has been proposed that declarative memory and priming might be related—for example, that conceptual priming results in more fluent processing, thereby providing a basis for familiarity judgments. In two experiments, we assessed conceptual priming and recognition memory across a 5-min interval in 5 memory-impaired patients. All patients exhibited fully intact priming in tests of both free association (study tent; at test, provide an association to canvas) and category verification (study lemon; at test, decide: Is lemon a type of fruit?). Yet the 2 most severely amnesic patients performed at chance on matched tests of recognition memory. These findings count against the notion that conceptual priming provides feelings of familiarity that can support accurate recognition judgments. We suggest that priming is inaccessible to conscious awareness and does not influence declarative memory. PMID:15447639

  15. Task-Dependent Masked Priming Effects in Visual Word Recognition

    PubMed Central

    Kinoshita, Sachiko; Norris, Dennis

    2012-01-01

    A method used widely to study the first 250 ms of visual word recognition is masked priming: These studies have yielded a rich set of data concerning the processes involved in recognizing letters and words. In these studies, there is an implicit assumption that the early processes in word recognition tapped by masked priming are automatic, and masked priming effects should therefore be invariant across tasks. Contrary to this assumption, masked priming effects are modulated by the task goal: For example, only word targets show priming in the lexical decision task, but both words and non-words do in the same-different task; semantic priming effects are generally weak in the lexical decision task but are robust in the semantic categorization task. We explain how such task dependence arises within the Bayesian Reader account of masked priming (Norris and Kinoshita, 2008), and how the task dissociations can be used to understand the early processes in lexical access. PMID:22675316

  16. Location invariance in masked repetition priming of letters and words.

    PubMed

    Marzouki, Yousri; Meeter, Martijn; Grainger, Jonathan

    2013-01-01

    Earlier studies have suggested that information from a prime stimulus can be integrated with target information even when the two stimuli appear at different spatial locations. Here, we examined such location invariance in a masked repetition priming paradigm with single letter and word stimuli. In order to neutralize effects of acuity and spatial attention on prime processing, subliminal prime stimuli always appeared on fixation. Target location varied randomly from trial to trial along the horizontal meridian at one of seven possible locations for letter stimuli (-7° to +7°) and three positions for word stimuli (-4°, 0°, +4°). Speed of responding to letter and word targets was affected by target location, and by priming, but the size of repetition priming effects did not vary as a function of target location. These results suggest that masked repetition priming is mediated by representations that integrate information about object identity independently of object location.

  17. Interviewing to elicit information: Using priming to promote disclosure.

    PubMed

    Dawson, Evan; Hartwig, Maria; Brimbal, Laure

    2015-10-01

    Research on implicit cognition has found that activating mental concepts can lead people to behave in ways that are consistent with the primed concept. In a pilot study we tested the effects of priming attachment security on the accessibility of disclosure-related concepts. Subsequently, we tested whether activating disclosure concepts by priming attachment security would influence people's forthcomingness. Participants (N = 102) delivered a flash drive to a confederate who exposed them to details of a mock eco terrorism conspiracy, which they were subsequently interviewed about. Before being interviewed, half of the participants were primed; the other half were not. Results showed that primed participants disclosed significantly more information than those who were not primed. Our findings highlight the need for further research on basic nonconscious processes in investigative interviews, as such influences can affect the outcome of the interview. The operation of nonconscious influences in such contexts has implications for practitioners, who may be able to utilize priming to facilitate disclosure.

  18. Detecting Prime Numbers via Roots of Polynomials

    ERIC Educational Resources Information Center

    Dobbs, David E.

    2012-01-01

    It is proved that an integer n [greater than or equal] 2 is a prime (resp., composite) number if and only if there exists exactly one (resp., more than one) nth-degree monic polynomial f with coefficients in Z[subscript n], the ring of integers modulo n, such that each element of Z[subscript n] is a root of f. This classroom note could find use in…

  19. The Actual Apollo 13 Prime Crew

    NASA Technical Reports Server (NTRS)

    1970-01-01

    The actual Apollo 13 lunar landing mission prime crew from left to right are: Commander, James A. Lovell Jr., Command Module pilot, John L. Swigert Jr.and Lunar Module pilot, Fred W. Haise Jr. The original Command Module pilot for this mission was Thomas 'Ken' Mattingly Jr. but due to exposure to German measles he was replaced by his backup, Command Module pilot, John L. 'Jack' Swigert Jr.

  20. Low energy electron beam induced vacancy activation in GaN

    SciTech Connect

    Nykaenen, H.; Suihkonen, S.; Sopanen, M.; Kilanski, L.

    2012-03-19

    Experimental evidence on low energy electron beam induced point defect activation in GaN grown by metal-organic vapor phase epitaxy (MOVPE) is presented. The GaN samples are irradiated with a 5-20 keV electron beam of a scanning electron microscope and investigated by photoluminescence and positron annihilation spectroscopy measurements. The degradation of the band-to-band luminescence of the irradiated GaN films is associated with the activation of point defects. The activated defects were identified as in-grown Ga-vacancies. We propose that MOVPE-GaN contains a significant concentration of passive V{sub Ga}-H{sub n} complexes that can be activated by H removal during low energy electron irradiation.

  1. Low energy electron beam induced vacancy activation in GaN

    NASA Astrophysics Data System (ADS)

    Nykänen, H.; Suihkonen, S.; Kilanski, L.; Sopanen, M.; Tuomisto, F.

    2012-03-01

    Experimental evidence on low energy electron beam induced point defect activation in GaN grown by metal-organic vapor phase epitaxy (MOVPE) is presented. The GaN samples are irradiated with a 5-20 keV electron beam of a scanning electron microscope and investigated by photoluminescence and positron annihilation spectroscopy measurements. The degradation of the band-to-band luminescence of the irradiated GaN films is associated with the activation of point defects. The activated defects were identified as in-grown Ga-vacancies. We propose that MOVPE-GaN contains a significant concentration of passive VGa-Hn complexes that can be activated by H removal during low energy electron irradiation.

  2. Study of electrical properties of single GaN nanowires grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Mozharov, A. M.; Komissarenko, F. E.; Vasiliev, A. A.; Bolshakov, A. D.; Moiseev, E. I.; Mukhin, M. S.; Cirlin, G. E.; Mukhin, I. S.

    2016-08-01

    Electrical properties of single GaN nanowires grown by means of molecular beam epitaxy with N-plasma source were studied. Ohmic contacts connected to single n-type GaN wires were produced by the combination of electron beam lithography, metal vacuum evaporation and rapid thermal annealing technique. The optimal annealing temperature to produce ohmic contacts implemented in the form of Ti/Al/Ti/Au stack has been determined. By means of 2-terminal measurement wiring diagram the conductivity of single NW has been obtained for NWs with different growth parameters. The method of MESFET measurement circuit layout of single GaN nanowires (NWs) has been developed. In accordance with performed numerical calculation, free carriers' concentration and mobility of single NWs could be independently estimated using MESFET structure.

  3. Semipolar AlN and GaN on Si(100): HVPE technology and layer properties

    NASA Astrophysics Data System (ADS)

    Bessolov, V.; Kalmykov, A.; Konenkova, E.; Kukushkin, S.; Myasoedov, A.; Poletaev, N.; Rodin, S.

    2017-01-01

    Hydride vapor phase epitaxy (HVPE) growth of semipolar AlN and GaN layers on planar Si(100) substrates with SiC nanolayer is investigated. It is shown experimentally that the solid-phase epitaxial formation of a specially oriented SiC nucleation layer followed by epitaxy of AlN layer by HVPE at low rates enables growth of aluminum and gallium nitrides in the semipolar direction. For the best GaN(20-23) layers obtained, the full width at half maximum (FWHM) value for the x-ray diffraction rocking curve is 24 arcmin. The photoluminescence spectrum of the semipolar GaN measured at 4 K exhibits bands related to basal-plane and prismatic stacking faults (BSF and PSF).

  4. Pyramidal defects in Mg-doped GaN in light of strain-energy minimization

    NASA Astrophysics Data System (ADS)

    Lee, Dong Nyung

    2011-12-01

    The planar segregation gives rise to stress and strain fields which are approximated by a uniaxial character in a displacement controlled system. In this condition, the elastic strain energy is proportional to Young's modulus. Young's modulus of GaN is minimized when the directions normal to a conical segregation surface make about 48° with the c-axis of hexagonal GaN, which is close to the angle 47.3° between the c-axis and the directions normal to the {112¯3} planes. This implies that the formation of pyramidal defects in magnesium-doped GaN can be a compromise between minimization of the elastic strain energy due to segregation of magnesium and the planar segregation.

  5. A low cost, green method to synthesize GaN nanowires

    PubMed Central

    Zhao, Jun-Wei; Zhang, Yue-Fei; Li, Yong-He; Su, Chao-hua; Song, Xue-Mei; Yan, Hui; Wang, Ru-Zhi

    2015-01-01

    The synthesis of gallium nitride nanowires (GaN NWs) by plasma enhanced chemical vapor deposition (PECVD) are successfully demonstrated in this work. The simple and green synthesis route is to introduce gallium oxide (Ga2O3) and nitrogen (N2) for the growth of nanowires. The prepared GaN nanowires have a single crystalline wurtzite structure, which the length of some nanowires is up to 20 μm, with a maximum diameter about 140 nm. The morphology and quantity of the nanowires can be modulated by the growth substrate and process parameters. In addition, the photoluminescence and field emission properties of the prepared GaN nanowires have been investigated, which were found to be largely affected by their structures. This work renders an environmentally benign strategy and a facile approach for controllable structures on nanodevice. PMID:26643613

  6. Lattice-matched HfN buffer layers for epitaxy of GaN on Si

    SciTech Connect

    Armitage, Robert; Yang, Qing; Feick, Henning; Gebauer, Joerg; Weber, Eicke R.; Shinkai, Satoko; Sasaki, Katsutaka

    2002-05-08

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 (mu)m. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  7. P-type doping of GaN(000\\bar{1}) by magnesium ion implantation

    NASA Astrophysics Data System (ADS)

    Narita, Tetsuo; Kachi, Tetsu; Kataoka, Keita; Uesugi, Tsutomu

    2017-01-01

    Magnesium ion implantation has been performed on a GaN(000\\bar{1}) substrate, whose surface has a high thermal stability, thus allowing postimplantation annealing without the use of a protective layer. The current-voltage characteristics of p-n diodes fabricated on GaN(000\\bar{1}) showed distinct rectification at a turn-on voltage of about 3 V, although the leakage current varied widely among the diodes. Coimplantation with magnesium and hydrogen ions effectively suppressed the leakage currents and device-to-device variations. In addition, an electroluminescence band was observed at wavelengths shorter than 450 nm for these diodes. These results provide strong evidence that implanted magnesium ions create acceptors in GaN(000\\bar{1}).

  8. Synthesis, morphology and optical properties of GaN and AlGaN semiconductor nanostructures

    SciTech Connect

    Kuppulingam, B. Singh, Shubra Baskar, K.

    2014-04-24

    Hexagonal Gallium Nitride (GaN) and Aluminum Gallium Nitride (AlGaN) nanoparticles were synthesized by sol-gel method using Ethylene Diamine Tetra Acetic acid (EDTA) complex route. Powder X-ray diffraction (PXRD) analysis confirms the hexagonal wurtzite structure of GaN and Al{sub 0.25}Ga{sub 0.75}N nanoparticles. Surface morphology and elemental analysis were carried out by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectroscopy (EDX). The room temperature Photoluminescence (PL) study shows the near band edge emission for GaN at 3.35 eV and at 3.59 eV for AlGaN nanoparticles. The Aluminum (Al) composition of 20% has been obtained from PL emission around 345 nm.

  9. Nonresonant tunneling phonon depopulated GaN based terahertz quantum cascade structures

    NASA Astrophysics Data System (ADS)

    Freeman, Will; Karunasiri, Gamani

    2013-04-01

    GaN based terahertz quantum cascade structures are theoretically studied. Since the Fröhlich interaction is ˜15 times higher in GaN than in GaAs, level broadening makes obtaining appreciable optical gain difficult even with a large population inversion. A density matrix Monte Carlo method is used to calculate the broadening of the optical gain spectra as a function of lattice temperature. We find by using a proposed method of nonresonant tunneling and electron-longitudinal-optical phonon scattering for depopulation of the lower lasing state, that it is possible to sufficiently isolate the upper lasing state and control the lower lasing state lifetime to obtain high optical gain in GaN. The results predict lasing out to 300 K which is significantly higher than for GaAs based structures.

  10. Visualization of GaN surface potential using terahertz emission enhanced by local defects

    NASA Astrophysics Data System (ADS)

    Sakai, Yuji; Kawayama, Iwao; Nakanishi, Hidetoshi; Tonouchi, Masayoshi

    2015-09-01

    Wide-gap semiconductors have received significant attention for their advantages over existing semiconductors in energy-efficient power devices. To realize stable and reliable wide-gap semiconductor devices, the basic physical properties, such as the electric properties on the surface and at the interface, should be revealed. Here, we report visualization of terahertz (THz) emission from the surface of GaN, which is excited by ultraviolet femtosecond laser pulses. We found that the THz emission is enhanced by defects related to yellow luminescence, and this phenomenon is explained through the modification of band structures in the surface depletion layer owing to trapped electrons at defect sites. Our results demonstrate that the surface potential in a GaN surface could be detected by laser-induced THz emission. Moreover, this method enables feasible evaluation of the distribution of non-radiative defects, which are undetectable with photoluminescence, and it contributes to the realization normally-off GaN devices.

  11. Visualization of GaN surface potential using terahertz emission enhanced by local defects.

    PubMed

    Sakai, Yuji; Kawayama, Iwao; Nakanishi, Hidetoshi; Tonouchi, Masayoshi

    2015-09-09

    Wide-gap semiconductors have received significant attention for their advantages over existing semiconductors in energy-efficient power devices. To realize stable and reliable wide-gap semiconductor devices, the basic physical properties, such as the electric properties on the surface and at the interface, should be revealed. Here, we report visualization of terahertz (THz) emission from the surface of GaN, which is excited by ultraviolet femtosecond laser pulses. We found that the THz emission is enhanced by defects related to yellow luminescence, and this phenomenon is explained through the modification of band structures in the surface depletion layer owing to trapped electrons at defect sites. Our results demonstrate that the surface potential in a GaN surface could be detected by laser-induced THz emission. Moreover, this method enables feasible evaluation of the distribution of non-radiative defects, which are undetectable with photoluminescence, and it contributes to the realization normally-off GaN devices.

  12. Long-Lived, Coherent Acoustic Phonon Oscillations in GaN Single Crystals

    SciTech Connect

    Wu, S.; Geiser, P.; Jun, J.; Karpinski, J.; Park, J.-R.; Sobolewski, R.

    2006-01-31

    We report on coherent acoustic phonon (CAP) oscillations studied in high-quality bulk GaN single crystals with a two-color femtosecond optical pump-probe technique. Using a far-above-the-band gap ultraviolet excitation (~270 nm wavelength) and a near-infrared probe beam (~810 nm wavelength), the long-lived, CAP transients were observed within a 10 ns time-delay window between the pump and probe pulses, with a dispersionless (proportional to the probe-beam wave vector) frequency of ~45 GHz. The measured CAP attenuation corresponded directly to the absorption of the probe light in bulk GaN, indicating that the actual (intrinsic) phonon-wave attenuation in our crystals was significantly smaller than the measured 65.8 cm^-1 value. The velocity of the phonon propagation was equal to the velocity of sound in GaN.

  13. Measurement of the electrostatic edge effect in wurtzite GaN nanowires

    SciTech Connect

    Henning, Alex; Rosenwaks, Yossi; Klein, Benjamin; Bertness, Kris A.; Blanchard, Paul T.; Sanford, Norman A.

    2014-11-24

    The electrostatic effect of the hexagonal corner on the electronic structure in wurtzite GaN nanowires (NWs) was directly measured using Kelvin probe force microscopy (KPFM). By correlating electrostatic simulations with the measured potential difference between the nanowire face and the hexagonal vertices, the surface state concentration and band bending of GaN NWs were estimated. The surface band bending is important for an efficient design of high electron mobility transistors and for opto-electronic devices based on GaN NWs. This methodology provides a way to extract NW parameters without making assumptions concerning the electron affinity. We are taking advantage of electrostatic modeling and the high precision that KPFM offers to circumvent a major source of uncertainty in determining the surface band bending.

  14. Migration mechanisms and diffusion barriers of carbon and native point defects in GaN

    NASA Astrophysics Data System (ADS)

    Kyrtsos, Alexandros; Matsubara, Masahiko; Bellotti, Enrico

    2016-06-01

    Carbon related defects are readily incorporated in GaN due to its abundance during growth both with MBE and MOCVD techniques. Employing first-principles calculations, we compute the migration barriers of carbon interstitials and we discuss possible relevant mechanisms of diffusion in the wurtzite GaN crystal. In addition, we calculate the migration barriers for the diffusion of the native defects of the crystal, i.e., gallium and nitrogen interstitials and vacancies. The minimum energy path and the migration barriers of these defects are obtained using the nudged elastic band method with the climbing image modification. In addition, the dimer method is used to independently determine the results. The results yield a quantitative description of carbon diffusion in GaN allowing for the determination of the most preferable migration paths.

  15. Investigation of HCl-based surface treatment for GaN devices

    SciTech Connect

    Okada, Hiroshi; Shinohara, Masatohi; Kondo, Yutaka; Sekiguchi, Hiroto; Yamane, Keisuke; Wakahara, Akihiro

    2016-02-01

    Surface treatments of GaN in HCl-based solutions are studied by X-ray photoelectron spectroscopy (XPS) and electrical characterization of fabricated GaN surfaces. A dilute-HCl treatment (HCl:H{sub 2}O=1:1) at room temperature and a boiled-HCl treatment (undiluted HCl) at 108°C are made on high-temperature annealed n-GaN. From the XPS study, removal of surface oxide by the dilute-HCl treatment was found, and more thoroughly oxide-removal was confirmed in the boiled-HCl treatment. Effect of the surface treatment on electrical characteristics on AlGaN/GaN transistor is also studied by applying treatment processes prior to the surface SiN deposition. Increase of drain current is found in boiled-HCl treated samples. The results suggest that the boiled-HCl treatment is effective for GaN device fabrication.

  16. Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

    NASA Astrophysics Data System (ADS)

    Calabrese, Gabriele; Corfdir, Pierre; Gao, Guanhui; Pfüller, Carsten; Trampert, Achim; Brandt, Oliver; Geelhaar, Lutz; Fernández-Garrido, Sergio

    2016-05-01

    We demonstrate the self-assembled growth of vertically aligned GaN nanowire ensembles on a flexible Ti foil by plasma-assisted molecular beam epitaxy. The analysis of single nanowires by transmission electron microscopy reveals that they are single crystalline. Low-temperature photoluminescence spectroscopy demonstrates that in comparison to standard GaN nanowires grown on Si, the nanowires prepared on the Ti foil exhibit an equivalent crystalline perfection, a higher density of basal-plane stacking faults, but a reduced density of inversion domain boundaries. The room-temperature photoluminescence spectrum of the nanowire ensemble is not influenced or degraded by the bending of the substrate. The present results pave the way for the fabrication of flexible optoelectronic devices based on GaN nanowires on metal foils.

  17. Electrical characterization of ensemble of GaN nanowires grown by the molecular beam epitaxy technique

    NASA Astrophysics Data System (ADS)

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Sobanska, M.; Klosek, K.

    2013-08-01

    High quality Schottky contacts are formed on GaN nanowires (NWs) structures grown by the molecular beam epitaxy technique on Si(111) substrate. The current-voltage characteristics show the rectification ratio of about 103 and the leakage current of about 10-4 A/cm2 at room temperature. From the capacitance-voltage measurements the free carrier concentration in GaN NWs is determined as about 1016 cm-3. Two deep levels (H200 and E280) are found in the structures containing GaN NWs. H200 is attributed to an extended defect located at the interface between the substrate and SiNx or near the sidewalls at the bottom of the NWs whereas E280 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

  18. Development of semipolar (11-22) LEDs on GaN templates

    NASA Astrophysics Data System (ADS)

    Corbett, B.; Quan, Z.; Dinh, D. V.; Kozlowski, G.; O'Mahony, D.; Akhter, M.; Schulz, S.; Parbrook, P.; Maaskant, P.; Caliebe, M.; Hocker, M.; Thonke, K.; Scholz, F.; Pristovsek, M.; Han, Y.; Humphreys, C. J.; Brunner, F.; Weyers, M.; Meyer, T. M.; Lymperakis, L.

    2016-03-01

    We report on blue and green light-emitting-diodes (LEDs) grown on (11-22)-GaN templates. The templates were created by overgrowth on structured r-plane sapphire substrates. Low defect density, 100 mm diameter GaN templates were obtained by metal organic vapour phase epitaxy (VPE) and hydride VPE techniques. Chemical-mechanical polishing was used to obtain smooth surfaces for the subsequent growth of LED structures. Ohmic contacts to the p-type GaN were obtained despite the lower activated acceptor levels. The LEDs show excellent output power and fast carrier dynamics. Freestanding LEDs have been obtained by use of laser-lift-off. The work is the result of collaboration under the European Union funded ALIGHT project.

  19. Strong photoluminescence emission from GaN grown on amorphous silica substrates by gas source MBE

    NASA Astrophysics Data System (ADS)

    Iwata, K.; Asahi, H.; Asami, K.; Kuroiwa, R.; Gonda, S.

    1998-06-01

    GaN layers are grown on amorphous fused silica glass substrates by gas source MBE using an ion removed electron cyclotron resonance (ECR) radical cell. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction measurements reveal that they are polycrystalline. However, they show a strong photoluminescence emission peak without deep level emission. The emission peak is red-shifted by about 150 meV from that of the excitonic emission peak of GaN grown on a sapphire substrate and has wide spectral half-width (˜250 meV at 77 K). The peak is not corresponding to the donor-acceptor pair (DAP) emission but is excitonic from the excitation power and temperature dependence of PL spectrum. These optical properties indicate that GaN layers grown on a glass substrate are promising for fabrication of large area and low cost light emitting devices and solar cells.

  20. A high efficiency C-band internally-matched harmonic tuning GaN power amplifier

    NASA Astrophysics Data System (ADS)

    Lu, Y.; Zhao, B. C.; Zheng, J. X.; Zhang, H. S.; Zheng, X. F.; Ma, X. H.; Hao, Y.; Ma, P. J.

    2016-09-01

    In this paper, a high efficiency C-band gallium nitride (GaN) internally-matched power amplifier (PA) is presented. This amplifier consists of 2-chips of self-developed GaN high-electron mobility transistors (HEMTs) with 16 mm total gate width on SiC substrate. New harmonic manipulation circuits are induced both in the input and output matching networks for high efficiency matching at fundamental and 2nd-harmonic frequency, respectively. The developed amplifier has achieved 72.1% power added efficiency (PAE) with 107.4 W output power at 5 GHz. To the best of our knowledge, this amplifier exhibits the highest PAE in C-band GaN HEMT amplifiers with over 100 W output power. Additionally, 1000 hours' aging test reveals high reliability for practical applications.