High pressure phase transitions in lawsonite at simultaneous high pressure and temperature: A single crystal study

NASA Astrophysics Data System (ADS)

O'Bannon, E. F., III; Vennari, C.; Beavers, C. C. G.; Williams, Q. C.

2015-12-01

Lawsonite (CaAl2Si2O7(OH)2.H2O) is a hydrous mineral with a high overall water content of ~11.5 wt.%. It is a significant carrier of water in subduction zones to depths greater than ~150 km. The structure of lawsonite has been extensively studied under room temperature, high-pressure conditions. However, simultaneous high-pressure and high-temperature experiments are scarce. We have conducted synchrotron-based simultaneous high-pressure and temperature single crystal experiments on lawsonite up to a maximum pressure of 8.4 GPa at ambient and high temperatures. We used a natural sample of lawsonite from Valley Ford, California (Sonoma County). At room pressure and temperature lawsonite crystallizes in the orthorhombic system with Cmcm symmetry. Room temperature compression indicates that lawsonite remains in the orthorhombic Cmcm space group up to ~9.0 GPa. Our 5.0 GPa crystal structure is similar to the room pressure structure, and shows almost isotropic compression of the crystallographic axes. Unit cell parameters at 5.0 GPa are a- 5.7835(10), b- 8.694(2), and c- 13.009(3). Single-crystal measurements at simultaneous high-pressure and temperature (e.g., >8.0 GPa and ~100 oC) can be indexed to a monoclinic P-centered unit cell. Interestingly, a modest temperature increase of ~100 oC appears to initiate the orthorhombic to monoclinic phase transition at ~0.6-2.4 GPa lower than room temperature compression studies have shown. There is no evidence of dehydration or H atom disorder under these conditions. This suggests that the orthorhombic to monoclinic transition could be kinetically impeded at 298 K, and that monoclinic lawsonite could be the dominant water carrier through much of the depth range of upper mantle subduction processes.

Magneto-optical Kerr effect of a Ni2.00Mn1.16Ga0.84 single crystal across austenite and intermartensite transitions

NASA Astrophysics Data System (ADS)

Fikáček, Jan; Heczko, Oleg; Kopecký, Vít; Kaštil, Jiří; Honolka, Jan

2018-04-01

We carried out magneto-optical Kerr effect (MOKE) and magnetization measurements on a single crystal of Ni2.00Mn1.16Ga0.84, which is a magnetic shape memory material with application potential for actuator devices or for energy recuperation. Up to the time of our study, there had been reports of MOKE measurements in polar geometry. Against earlier predictions, we show that surface magnetic states of the martensite and the austenite can be also probed efficiently via longitudinal MOKE. A single-variant magnetic state prepared at room temperature is characterized by square-shaped ferromagnetic hysteresis loops yielding coercive fields, which are key material properties for future applications. Temperature dependencies of Kerr rotation were found to be linearly proportional to magnetization for martensitic phases. After passing through an inter-martensitic structural transition below room temperature in zero magnetic field, the coercive fields are more than doubled in comparison with the room temperature values. Above room temperature where an austenite structure is formed, MOKE signals are dominated by quadratic contributions and the magnitude of Kerr rotation drops due to changes in the electronic and magnetic domains structure.

A Two-Dimensional Manganese Gallium Nitride Surface Structure Showing Ferromagnetism at Room Temperature.

PubMed

Ma, Yingqiao; Chinchore, Abhijit V; Smith, Arthur R; Barral, María Andrea; Ferrari, Valeria

2018-01-10

Practical applications of semiconductor spintronic devices necessitate ferromagnetic behavior at or above room temperature. In this paper, we demonstrate a two-dimensional manganese gallium nitride surface structure (MnGaN-2D) which is atomically thin and shows ferromagnetic domain structure at room temperature as measured by spin-resolved scanning tunneling microscopy and spectroscopy. Application of small magnetic fields proves that the observed magnetic domains follow a hysteretic behavior. Two initially oppositely oriented MnGaN-2D domains are rotated into alignment with only 120 mT and remain mostly in alignment at remanence. The measurements are further supported by first-principles theoretical calculations which reveal highly spin-polarized and spin-split surface states with spin polarization of up to 95% for manganese local density of states.

Accessing protein conformational ensembles using room-temperature X-ray crystallography

PubMed Central

Fraser, James S.; van den Bedem, Henry; Samelson, Avi J.; Lang, P. Therese; Holton, James M.; Echols, Nathaniel; Alber, Tom

2011-01-01

Modern protein crystal structures are based nearly exclusively on X-ray data collected at cryogenic temperatures (generally 100 K). The cooling process is thought to introduce little bias in the functional interpretation of structural results, because cryogenic temperatures minimally perturb the overall protein backbone fold. In contrast, here we show that flash cooling biases previously hidden structural ensembles in protein crystals. By analyzing available data for 30 different proteins using new computational tools for electron-density sampling, model refinement, and molecular packing analysis, we found that crystal cryocooling remodels the conformational distributions of more than 35% of side chains and eliminates packing defects necessary for functional motions. In the signaling switch protein, H-Ras, an allosteric network consistent with fluctuations detected in solution by NMR was uncovered in the room-temperature, but not the cryogenic, electron-density maps. These results expose a bias in structural databases toward smaller, overpacked, and unrealistically unique models. Monitoring room-temperature conformational ensembles by X-ray crystallography can reveal motions crucial for catalysis, ligand binding, and allosteric regulation. PMID:21918110

Improvement of Superplasticity in High-Mg Aluminum Alloys by Sacrifice of Some Room Temperature Formability

NASA Astrophysics Data System (ADS)

Jin, H.; Amirkhiz, B. Shalchi; Lloyd, D. J.

2018-03-01

The mechanical properties of fully annealed Al-4.6 wt pct Mg alloys with different levels of Mn and Fe have been characterized at room and superplastic forming (SPF) temperatures. The effects of Mn and Fe on the intermetallic phase, grain structure, and cavitation were investigated and correlated to the formability at different temperatures. Although both Mn and Fe contribute to the formation of Al6(Mn,Fe) phase, which refines the grain structure by particle-stimulated nucleation and Zener pinning, their effects are different. An increasing Mn reduces the room temperature formability due to the increasing number of intermetallic particles, but significantly improves the superplasticity by fine grain size-induced grain boundary sliding. Meanwhile, the Fe makes the constituent particles very coarse, resulting in reduced formability at all temperatures due to extensive cavitation. A combination of high Mn and low Fe is therefore beneficial to SPF, while low levels of both elements are good for cold forming. Consequently, the superplasticity of high-Mg aluminum alloys can be significantly improved by modifying the chemical composition with sacrifice of some room temperature formability.

Does Z' equal 1 or 2? Enhanced powder NMR crystallography verification of a disordered room temperature crystal structure of a p38 inhibitor for chronic obstructive pulmonary disease.

PubMed

Widdifield, Cory M; Nilsson Lill, Sten O; Broo, Anders; Lindkvist, Maria; Pettersen, Anna; Svensk Ankarberg, Anna; Aldred, Peter; Schantz, Staffan; Emsley, Lyndon

2017-06-28

The crystal structure of the Form A polymorph of N-cyclopropyl-3-fluoro-4-methyl-5-[3-[[1-[2-[2-(methylamino)ethoxy]phenyl]cyclopropyl]amino]-2-oxo-pyrazin-1-yl]benzamide (i.e., AZD7624), determined using single-crystal X-ray diffraction (scXRD) at 100 K, contains two molecules in the asymmetric unit (Z' = 2) and has regions of local static disorder. This substance has been in phase IIa drug development trials for the treatment of chronic obstructive pulmonary disease, a disease which affects over 300 million people and contributes to nearly 3 million deaths annually. While attempting to verify the crystal structure using nuclear magnetic resonance crystallography (NMRX), we measured 13 C solid-state NMR (SSNMR) spectra at 295 K that appeared consistent with Z' = 1 rather than Z' = 2. To understand this surprising observation, we used multinuclear SSNMR ( 1 H, 13 C, 15 N), gauge-including projector augmented-wave density functional theory (GIPAW DFT) calculations, crystal structure prediction (CSP), and powder XRD (pXRD) to determine the room temperature crystal structure. Due to the large size of AZD7624 (ca. 500 amu, 54 distinct 13 C environments for Z' = 2), static disorder at 100 K, and (as we show) dynamic disorder at ambient temperatures, NMR spectral assignment was a challenge. We introduce a method to enhance confidence in NMR assignments by comparing experimental 13 C isotropic chemical shifts against site-specific DFT-calculated shift distributions established using CSP-generated crystal structures. The assignment and room temperature NMRX structure determination process also included measurements of 13 C shift tensors and the observation of residual dipolar coupling between 13 C and 14 N. CSP generated ca. 90 reasonable candidate structures (Z' = 1 and Z' = 2), which when coupled with GIPAW DFT results, room temperature pXRD, and the assigned SSNMR data, establish Z' = 2 at room temperature. We find that the polymorphic Form A of AZD7624 is maintained at room temperature, although dynamic disorder is present on the NMR timescale. Of the CSP-generated structures, 2 are found to be fully consistent with the SSNMR and pXRD data; within this pair, they are found to be structurally very similar (RMSD 16 = 0.30 Å). We establish that the CSP structure in best agreement with the NMR data possesses the highest degree of structural similarity with the scXRD-determined structure (RMSD 16 = 0.17 Å), and has the lowest DFT-calculated energy amongst all CSP-generated structures with Z' = 2.

Comparative studies on the room-temperature ferrielectric and ferrimagnetic Ni3TeO6-type A2FeMoO6 compounds (A = Sc, Lu)

PubMed Central

Song, Guang; Zhang, Weiyi

2016-01-01

First-principles calculations have been carried out to study the structural, electric, and magnetic properties of Ni3TeO6-type A2FeMoO6 compounds (A = Sc, Lu). Their electric and magnetic properties behave like room-temperature ferrielectric and ferrimagnetic insulators where polarization comes from the un-cancelled antiparallel dipoles of (A(1), Fe3+) and (A(2), Mo3+) ion groups, and magnetization from un-cancelled antiparallel moments of Fe3+ and Mo3+ ions. The net polarization increases with A’s ionic radius and is 7.1 and 8.7 μCcm−2 for Sc2FeMoO6 and Lu2FeMoO6, respectively. The net magnetic moment is 2 μB per formula unit. The magnetic transition temperature is estimated well above room-temperature due to the strong antiferromagnetic superexchange coupling among Fe3+ and Mo3+ spins. The estimated paraelectric to ferrielectric transition temperature is also well above room-temperature. Moreover, strong magnetoelectric coupling is also anticipated because the magnetic ions are involved both in polarization and magnetization. The fully relaxed Ni3TeO6-type A2FeMoO6 structures are free from soft-phonon modes and correspond to stable structures. As a result, Ni3TeO6-type A2FeMoO6 compounds are possible candidates for room-temperature multiferroics with large magnetization and polarization. PMID:26831406

Room-temperature serial crystallography at synchrotron X-ray sources using slowly flowing free-standing high-viscosity microstreams.

PubMed

Botha, Sabine; Nass, Karol; Barends, Thomas R M; Kabsch, Wolfgang; Latz, Beatrice; Dworkowski, Florian; Foucar, Lutz; Panepucci, Ezequiel; Wang, Meitian; Shoeman, Robert L; Schlichting, Ilme; Doak, R Bruce

2015-02-01

Recent advances in synchrotron sources, beamline optics and detectors are driving a renaissance in room-temperature data collection. The underlying impetus is the recognition that conformational differences are observed in functionally important regions of structures determined using crystals kept at ambient as opposed to cryogenic temperature during data collection. In addition, room-temperature measurements enable time-resolved studies and eliminate the need to find suitable cryoprotectants. Since radiation damage limits the high-resolution data that can be obtained from a single crystal, especially at room temperature, data are typically collected in a serial fashion using a number of crystals to spread the total dose over the entire ensemble. Several approaches have been developed over the years to efficiently exchange crystals for room-temperature data collection. These include in situ collection in trays, chips and capillary mounts. Here, the use of a slowly flowing microscopic stream for crystal delivery is demonstrated, resulting in extremely high-throughput delivery of crystals into the X-ray beam. This free-stream technology, which was originally developed for serial femtosecond crystallography at X-ray free-electron lasers, is here adapted to serial crystallography at synchrotrons. By embedding the crystals in a high-viscosity carrier stream, high-resolution room-temperature studies can be conducted at atmospheric pressure using the unattenuated X-ray beam, thus permitting the analysis of small or weakly scattering crystals. The high-viscosity extrusion injector is described, as is its use to collect high-resolution serial data from native and heavy-atom-derivatized lysozyme crystals at the Swiss Light Source using less than half a milligram of protein crystals. The room-temperature serial data allow de novo structure determination. The crystal size used in this proof-of-principle experiment was dictated by the available flux density. However, upcoming developments in beamline optics, detectors and synchrotron sources will enable the use of true microcrystals. This high-throughput, high-dose-rate methodology provides a new route to investigating the structure and dynamics of macromolecules at ambient temperature.

Wide bandgap BaSnO3 films with room temperature conductivity exceeding 104 S cm−1

PubMed Central

Prakash, Abhinav; Xu, Peng; Faghaninia, Alireza; Shukla, Sudhanshu; Ager, Joel W.; Lo, Cynthia S.; Jalan, Bharat

2017-01-01

Wide bandgap perovskite oxides with high room temperature conductivities and structural compatibility with a diverse family of organic/inorganic perovskite materials are of significant interest as transparent conductors and as active components in power electronics. Such materials must also possess high room temperature mobility to minimize power consumption and to enable high-frequency applications. Here, we report n-type BaSnO3 films grown using hybrid molecular beam epitaxy with room temperature conductivity exceeding 104 S cm−1. Significantly, these films show room temperature mobilities up to 120 cm2 V−1 s−1 even at carrier concentrations above 3 × 1020 cm−3 together with a wide bandgap (3 eV). We examine the mobility-limiting scattering mechanisms by calculating temperature-dependent mobility, and Seebeck coefficient using the Boltzmann transport framework and ab-initio calculations. These results place perovskite oxide semiconductors for the first time on par with the highly successful III–N system, thereby bringing all-transparent, high-power oxide electronics operating at room temperature a step closer to reality. PMID:28474675

Wide bandgap BaSnO 3 films with room temperature conductivity exceeding 10 4 S cm -1

DOE PAGES

Prakash, Abhinav; Xu, Peng; Faghaninia, Alireza; ...

2017-05-05

Wide bandgap perovskite oxides with high room temperature conductivities and structural compatibility with a diverse family of organic/inorganic perovskite materials are of sign ificant interest as transparent conductors and as active components in power electronics. Such materials must also possess high room temperature mobility to minimize power consumption and to enable high-frequency applications. Here, we report n-type BaSnO 3 films grown using hybrid molecular beam epitaxy with room temperature conductivity exceeding 10 4 S cm -1 . Significantly, these films show room temperature mobilities up to 120 cm 2 V -1 s -1 even at carrier concentrations abovemore » 3 × 10 20 cm -3 together with a wide bandgap (3 eV). We examine the mobility-limiting scattering mechanisms by calculating temperature-dependent mobility, and Seebeck coefficient using the Boltzmann transport framework and ab-initio calculations. These results place perovskite oxide semiconductors for the first time on par with the highly successful III-N system, thereby bringing all-transparent, high-power oxide electronics operating at room temperature a step closer to reality.« less

Highly responsive ground state of PbTaSe 2 : Structural phase transition and evolution of superconductivity under pressure

DOE PAGES

Kaluarachchi, Udhara S.; Deng, Yuhang; Besser, Matthew F.; ...

2017-06-09

Transport and magnetic studies of PbTaSe 2 under pressure suggest the existence of two superconducting phases with the low temperature phase boundary at ~ 0.25 GPa that is defined by a very sharp, first order, phase transition. The first order phase transition line can be followed via pressure dependent resistivity measurements, and is found to be near 0.12 GPa near room temperature. Transmission electron microscopy and x-ray diffraction at elevated temperatures confirm that this first order phase transition is structural and occurs at ambient pressure near ~ 425 K. The new, high temperature/high pressure phase has a similar crystal structuremore » and slightly lower unit cell volume relative to the ambient pressure, room temperature structure. Based on first-principles calculations this structure is suggested to be obtained by shifting the Pb atoms from the 1 a to 1 e Wyckoff position without changing the positions of Ta and Se atoms. PbTaSe 2 has an exceptionally pressure sensitive, structural phase transition with Δ T s / Δ P ≈ -1400 K/GPa near room temperature, and ≈ -1700 K/GPa near 4 K. This first order transition causes a ~ 1 K (~ 25 % ) steplike decrease in T c as pressure is increased through 0.25 GPa.« less

Broad-gain (Δλ/λ0

PubMed

Fujita, Kazuue; Furuta, Shinichi; Dougakiuchi, Tatsuo; Sugiyama, Atsushi; Edamura, Tadataka; Yamanishi, Masamichi

2011-01-31

Broad-gain operation of λ~8.7 μm quantum cascade lasers based on dual-upper-state to multiple-lower-state transition design is reported. The devices exhibit surprisingly wide (~500 cm(-1)) electroluminescence spectra which are very insensitive to voltage and temperature changes above room temperature. With recourse to the temperature-insensitivity of electroluminescence spectra, the lasers demonstrate an extremely-weak temperature-dependence of laser performances: T0-value of 510 K, associated with a room temperature threshold current density of 2.6 kA/cm2. In addition, despite such wide gain spectra, room temperature, continuous wave operation of the laser with buried hetero structure is achieved.

Room temperature ferromagnetism in BiFe1-xMnxO3 thin film induced by spin-structure manipulation

NASA Astrophysics Data System (ADS)

Shigematsu, Kei; Asakura, Takeshi; Yamamoto, Hajime; Shimizu, Keisuke; Katsumata, Marin; Shimizu, Haruki; Sakai, Yuki; Hojo, Hajime; Mibu, Ko; Azuma, Masaki

2018-05-01

The evolution of crystal structure, spin structure, and macroscopic magnetization of manganese-substituted BiFeO3 (BiFe1-xMnxO3), a candidate for multiferroic materials, were investigated on bulk and epitaxial thin-film. Mn substitution for Fe induced collinear antiferromagnetic spin structure around room temperature by destabilizing the cycloidal spin modulation which prohibited the appearance of net magnetization generated by Dzyaloshinskii-Moriya interaction. For the bulk samples, however, no significant signal of ferromagnetism was observed because the direction of the ordered spins was close to parallel to the electric polarization so that spin-canting did not occur. On the contrary, BiFe1-xMnxO3 thin film on SrTiO3 (001) had a collinear spin structure with the spin direction perpendicular to the electric polarization at room temperature, where the appearance of spontaneous magnetization was expected. Indeed, ferromagnetic hysteresis behavior was observed for BiFe0.9Mn0.1O3 thin film.

High pressure–low temperature phase diagram of barium: Simplicity versus complexity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desgreniers, Serge; Tse, John S., E-mail: John.Tse@usask.ca; State Key Laboratory of Superhard Materials, Jilin University, 130012 Changchun

2015-11-30

Barium holds a distinctive position among all elements studied upon densification. Indeed, it was the first example shown to violate the long-standing notion that high compression of simple metals should preserve or yield close-packed structures. From modest pressure conditions at room temperature, barium transforms at higher pressures from its simple structures to the extraordinarily complex atomic arrangements of the incommensurate and self-hosting Ba-IV phases. By a detailed mapping of the pressure/temperature structures of barium, we demonstrate the existence of another crystalline arrangement of barium, Ba-VI, at low temperature and high pressure. The simple structure of Ba-VI is unlike that ofmore » complex Ba-IV, the phase encountered in a similar pressure range at room temperature. First-principles calculations predict Ba-VI to be stable at high pressure and superconductive. The results illustrate the complexity of the low temperature-high pressure phase diagram of barium and the significant effect of temperature on structural phase transformations.« less

Super-formable pure magnesium at room temperature.

PubMed

Zeng, Zhuoran; Nie, Jian-Feng; Xu, Shi-Wei; H J Davies, Chris; Birbilis, Nick

2017-10-17

Magnesium, the lightest structural metal, is difficult to form at room temperature due to an insufficient number of deformation modes imposed by its hexagonal structure and a strong texture developed during thermomechanical processes. Although appropriate alloying additions can weaken the texture, formability improvement is limited because alloying additions do not fundamentally alter deformation modes. Here we show that magnesium can become super-formable at room temperature without alloying. Despite possessing a strong texture, magnesium can be cold rolled to a strain at least eight times that possible in conventional processing. The resultant cold-rolled sheet can be further formed without cracking due to grain size reduction to the order of one micron and inter-granular mechanisms becoming dominant, rather than the usual slip and twinning. These findings provide a pathway for developing highly formable products from magnesium and other hexagonal metals that are traditionally difficult to form at room temperature.Replacing steel or aluminium vehicle parts with magnesium would result in reduced emissions, but shaping magnesium without cracking remains challenging. Here, the authors successfully extrude and roll textured magnesium into ductile foil at low temperatures by activating intra-granular mechanisms.

Thermostability of bovine submaxillary mucin (BSM) in bulk solution and at a sliding interface.

PubMed

Madsen, Jan Busk; Pakkanen, Kirsi I; Lee, Seunghwan

2014-06-15

Thermostability of bovine submaxillary mucin (BSM) was studied in terms of its structure, hydrodynamic size, surface adsorption, and lubricating properties in the temperature range of 5-85°C. The overall random coil structure of BSM showed a gradual loosening with increasing temperature as characterized by circular dichroism (CD) spectroscopy, but this change was fully reversible upon lowering temperature. Extended heating up to 120 min at 80°C did not make any appreciable changes in the structure of BSM when it was cooled to room temperature. The hydrodynamic size of BSM, as studied by dynamic light scattering (DLS), showed a slight increase after heating at high temperature (80°C). Optical waveguide lightmode spectroscopy (OWLS) studies showed facile adsorption of BSM onto poly(dimethylsiloxane) (PDMS) surface (>180 ng/cm(2)) at room temperature due to its amphiphilic characteristics. Adsorbed mass of BSM was noticeably reduced after heating at 80°C, possibly resulting from its aggregation. BSM showed excellent lubricity at self-mated sliding contacts between PDMS at room temperature or lower (friction coefficient≈0.02), even when BSM solution was pre-heated up to 120 min at 80°C. Gradual degradation of lubricity of BSM was observed with increasing temperature, but it was also reversibly recovered with decreasing temperature. Structural and functional stability of BSM against heating is proposed to originate from heavy glycosylation and lack of higher degree of protein structure in BSM. Copyright © 2014 Elsevier Inc. All rights reserved.

Temperature evolution of the structural properties of monodomain ferroelectric thin film

NASA Astrophysics Data System (ADS)

Janolin, Pierre-Eymeric; Le Marrec, Françoise; Chevreul, Jacques; Dkhil, Brahim

2007-05-01

The structural evolution of epitaxial monodomain (only 180° domains) ferroelectric PbTiO3 thin film has been investigated, using high-resolution, temperature-dependent, x-ray diffraction. The full set of lattice parameters was obtained from room temperature up to 850K. It allowed the calculation of the different strains stored in the film at room temperature, underlying the difference between the mechanical strain and the misfit strain. The evolution of the misfit strain as a function of temperature was also calculated and was found to be consistent with the theoretical temperature-misfit strain phase diagram. These data strongly suggest that the film remains ferroelectric and tetragonal up to 940K.

The Conformational Flexibility of the Acyltransferase from the Disorazole Polyketide Synthase Is Revealed by an X-ray Free-Electron Laser Using a Room-Temperature Sample Delivery Method for Serial Crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mathews, Irimpan I.; Allison, Kim; Robbins, Thomas

The crystal structure of the trans-acyltransferase (AT) from the disorazole polyketide synthase (PKS) was determined at room temperature to a resolution of 2.5 Å using a new method for sample delivery directly into an X-ray free-electron laser. A novel sample extractor efficiently delivered limited quantities of microcrystals directly from the native crystallization solution into the X-ray beam at room temperature. The AT structure revealed important catalytic features of this core PKS enzyme, including the occurrence of conformational changes around the active site. The implications of these conformational changes on polyketide synthase reaction dynamics are discussed.

The Conformational Flexibility of the Acyltransferase from the Disorazole Polyketide Synthase Is Revealed by an X-ray Free-Electron Laser Using a Room-Temperature Sample Delivery Method for Serial Crystallography

DOE PAGES

Mathews, Irimpan I.; Allison, Kim; Robbins, Thomas; ...

2017-08-23

The crystal structure of the trans-acyltransferase (AT) from the disorazole polyketide synthase (PKS) was determined at room temperature to a resolution of 2.5 Å using a new method for sample delivery directly into an X-ray free-electron laser. A novel sample extractor efficiently delivered limited quantities of microcrystals directly from the native crystallization solution into the X-ray beam at room temperature. The AT structure revealed important catalytic features of this core PKS enzyme, including the occurrence of conformational changes around the active site. The implications of these conformational changes on polyketide synthase reaction dynamics are discussed.

On-site chemical pre-lithiation of S cathode at room temperature on a 3D nano-structured current collector

NASA Astrophysics Data System (ADS)

Wu, Yunwen; Momma, Toshiyuki; Ahn, Seongki; Yokoshima, Tokihiko; Nara, Hiroki; Osaka, Tetsuya

2017-10-01

This work reports a new chemical pre-lithiation method to fabricate lithium sulfide (Li2S) cathode. This pre-lithiation process is taken place simply by dropping the organolithium reagent lithium naphthalenide (Li+Naph-) on the prepared sulfur cathode. It is the first time realizing the room temperature chemical pre-lithaition reaction attributed by the 3D nanostructured carbon nanotube (CNT) current collector. It is confirmed that the Li2S cathode fabricated at room temperature showing higher capacity and lower hysteresis than the Li2S cathode fabricated at high temperature pre-lithiation. The pre-lithiated Li2S cathode at room temperature shows stable cycling performance with a 600 mAh g-1 capacity after 100 cycles at 0.1 C-rate and high capacity of 500 mAh g-1 at 2 C-rate. This simple on-site pre-lithiation method at room temperature is demonstrated to be applicable for the in-situ pre-lithiation in a Li metal free battery.

The influences of fluorine and process variations on polysilicon film stress and MOSFET hot carrier effects

NASA Technical Reports Server (NTRS)

Lowry, Lynn E.; Macwilliams, Kenneth P.; Isaac, Mary

1991-01-01

The use of fluorinated gate oxides may provide an improvement in nMOSFET reliability by enhancing hot carrier resistance. In order to clarify the mechanisms by which polysilicon processing and fluorination influence the oxide behavior, a matrix of nMOSFET structures was prepared using various processing, doping, and implantation strategies. These structures were evaluated for crystalline morphology and chemical element distribution. Mechanical stress measurements were taken on the polysilicon films from room temperature to cryogenic temperature. These examinations showed that fluorination of a structure with randomly oriented polysilicon can reduce residual mechanical stress and improve hot carrier resistance at room temperature.

Thermal Characterization and Flammability of Structural Epoxy Adhesive and Carbon/Epoxy Composite with Environmental and Chemical Degradation (Postprint)

DTIC Science & Technology

2012-01-01

this study). TGA scans show the thermal degradation of carbon/ epoxy composite by fuel additive at room temperature. Through Microscale Combustion...concerns regarding the durability of structural epoxy adhesive contaminated by hydraulic fluid or fuel additive , under simplified test conditions (no...higher than room tem- perature) or fuel additive (at all temperatures of this study). TGA scans show the thermal degradation of carbon/ epoxy composite

Room-temperature synthesis of core-shell structured magnetic covalent organic frameworks for efficient enrichment of peptides and simultaneous exclusion of proteins.

PubMed

Lin, Guo; Gao, Chaohong; Zheng, Qiong; Lei, Zhixian; Geng, Huijuan; Lin, Zian; Yang, Huanghao; Cai, Zongwei

2017-03-28

Core-shell structured magnetic covalent organic frameworks (Fe 3 O 4 @COFs) were synthesized via a facile approach at room temperature. Combining the advantages of high porosity, magnetic responsiveness, chemical stability and selectivity, Fe 3 O 4 @COFs can serve as an ideal absorbent for the highly efficient enrichment of peptides and the simultaneous exclusion of proteins from complex biological samples.

The room-temperature synthesis of anisotropic CdHgTe quantum dot alloys: a "molecular welding" effect.

PubMed

Taniguchi, Shohei; Green, Mark; Lim, Teck

2011-03-16

The room-temperature chemical transformation of spherical CdTe nanoparticles into anisotropic alloyed CdHgTe particles using mercury bromide in a toluene/methanol system at room temperature has been investigated. The resulting materials readily dissolved in toluene and exhibited a significant red-shift in the optical properties toward the infrared region. Structural transformations were observed, with electron microscopy showing that the CdTe nanoparticles were chemically attached ('welded') to other CdTe nanoparticles, creating highly complex anisotropic heterostructures which also incorporated mercury.

Synthesis and characterization of CoPt nanoparticles prepared by room temperature chemical reduction with PAMAM dendrimer as template.

PubMed

Wan, Haiying; Shi, Shifan; Bai, Litao; Shamsuzzoha, Mohammad; Harrell, J W; Street, Shane C

2010-08-01

We describe an approach to synthesize monodisperse CoPt nanoparticles with dendrimer as template by a simple chemical reduction method in aqueous solution using NaBH4 as reducing agent at room temperature. The as-made CoPt nanoparticles buried in the dendrimer matrix have the chemically disordered fcc structure and can be transformed to the fct phase after annealing at 700 degrees C. This is the first report of dendrimer-mediated room temperature synthesis of monodisperse magnetic nanoparticles in aqueous solution.

Paramagnetic-to-nonmagnetic transition in antiperovskite nitride Cr3GeN studied by 14N-NMR and µSR

NASA Astrophysics Data System (ADS)

Takao, K.; Liu, Z.; Uji, K.; Waki, T.; Tabata, Y.; Watanabe, I.; Nakamura, H.

2017-06-01

The antiperovskite-related nitride Cr3GeN forms a tetragonal structure with the space group P\\bar{4}{2}1m at room temperature. It shows a tetragonal (P\\bar{4}{2}1m) to tetragonal (I4/mcm) structural transition with a large hysteresis at 300-400 K. The magnetic susceptibility of Cr3GeN shows Curie-Weiss type temperature dependence at high temperature, but is almost temperature-independent below room temperature. We carried out µSR and 14N-NMR microscopy measurements to reveal the magnetic ground state of Cr3GeN. Gradual muon spin relaxation, which is nearly temperature-independent below room temperature, was observed, indicating that Cr3GeN is magnetically inactive. In the 14N-NMR measurement, a quadrupole-split spectrum was obtained at around 14 K = 0. The temperature dependence of 14(1/T1) satisfies the Korringa relation. These experimental results indicate that the ground state of Cr3GeN is Pauli paramagnetic, without antiferromagnetic long-range order.

Structure of Room Temperature Ionic Liquids on Charged Graphene: An integrated experimental and computational study

NASA Astrophysics Data System (ADS)

Uysal, Ahmet; Zhou, Hua; Lee, Sang Soo; Fenter, Paul; Feng, Guang; Li, Song; Cummings, Peter; Fulvio, Pasquale; Dai, Sheng; McDonough, Jake; Gogotsi, Yury

2014-03-01

Electrical double layer capacitors (EDLCs) with room temperature ionic liquid (RTIL) electrolytes and carbon electrodes are promising candidates for energy storage devices with high power density and long cycle life. We studied the potential and time dependent changes in the electric double layer (EDL) structure of an imidazolium-based room temperature ionic liquid (RTIL) electrolyte at an epitaxial graphene (EG) surface. We used in situ x-ray reflectivity (XR) to determine the EDL structure at static potentials, during cyclic voltammetry (CV) and potential step measurements. The static potential structures were also investigated with fully atomistic molecular dynamics (MD) simulations. Combined XR and MD results show that the EDL structure has alternating anion/cation layers within the first nanometer of the interface. The dynamical response of the EDL to potential steps has a slow component (>10 s) and the RTIL structure shows hysteresis during CV scans. We propose a conceptual model that connects nanoscale interfacial structure to the macroscopic measurements. This material is based upon work supported as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science (SC), Office of Basic Energy

Nickel aluminide alloy suitable for structural applications

DOEpatents

Liu, Chain T.

1998-01-01

Alloys for use in structural applications based upon NiAl to which are added selected elements to enhance room temperature ductility and high temperature strength. Specifically, small additions of molybdenum produce a beneficial alloy, while further additions of boron, carbon, iron, niobium, tantalum, zirconium and hafnium further improve performance of alloys at both room temperature and high temperatures. A preferred alloy system composition is Ni--(49.1.+-.0.8%)Al--(1.0.+-.0.8%)Mo--(0.7.+-.0.5%)Nb/Ta/Zr/Hf--(nearly zero to 0.03%)B/C, where the % is at. % in each of the concentrations. All alloys demonstrated good oxidation resistance at the elevated temperatures. The alloys can be fabricated into components using conventional techniques.

Pronounced pre-martensitic anomaly in the magnetization on Ni2MnGa thin films

NASA Astrophysics Data System (ADS)

Neckel, I. T.; Müller, C.; Nobrega, K. Z.; Dartora, C. A.; Schreiner, W. H.; Mosca, D. H.

2018-05-01

We have prepared [110]-textured Ni2MnGa thin films exhibiting an unusual pre-martensitic transition accompanied by an extremely large magnetization change. The thin films were grown by molecular beam epitaxy directly on epi-ready GaAs(111)B. Crystalline structure was investigated in situ by reflection high-energy electron diffraction (RHEED) and ex situ by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the film exhibits cubic crystalline structure (L2 1) at room temperature with lattice parameter a = 5.88 Å which undergoes martensitic transition. Magnetic characterization shows ferromagnetic behavior at room temperature with Curie temperature higher than room temperature. Martensitic transformation occurs at TM ∼ 185 K. A phenomenological model based on Landau theory of phase transformation was developed to explain the anomalous pre-martensitic transition at ∼285 K.

The Conformational Flexibility of the Acyltransferase from the Disorazole Polyketide Synthase Is Revealed by an X-ray Free-Electron Laser Using a Room-Temperature Sample Delivery Method for Serial Crystallography

PubMed Central

Allison, Kim; Robbins, Thomas; Lyubimov, Artem Y.; Uervirojnangkoorn, Monarin; Brunger, Axel T.; Khosla, Chaitan; DeMirci, Hasan; McPhillips, Scott E.; Hollenbeck, Michael; Soltis, Michael; Cohen, Aina E.

2017-01-01

The crystal structure of the trans-acyltrans-ferase (AT) from the disorazole polyketide synthase (PKS) was determined at room temperature to a resolution of 2.5 Å using a new method for the direct delivery of the sample into an X-ray free-electron laser. A novel sample extractor efficiently delivered limited quantities of microcrystals directly from the native crystallization solution into the X-ray beam at room temperature. The AT structure revealed important catalytic features of this core PKS enzyme, including the occurrence of conformational changes around the active site. The implications of these conformational changes for polyketide synthase reaction dynamics are discussed. PMID:28832129

Reversible photoinduced spectral change in Eu2O3 at room temperature

NASA Astrophysics Data System (ADS)

Mochizuki, Shosuke; Nakanishi, Tauto; Suzuki, Yuya; Ishi, Kimihiro

2001-12-01

When Eu2O3 powder compact and film are irradiated with ultraviolet (UV) laser light in a vacuum, their photoluminescence (PL) spectra change from a red sharp-line structure to a white broad band, which can be clearly seen with the naked eye. After removing the UV laser light, the white PL continues for more than several months at room temperature under room light, in spite of any changes of atmosphere. By irradiating with the same UV laser light at room temperature under O2 gas atmosphere, the original red PL state reappears. Such a reversible phenomenon may well yield materials for white-light-emitting devices and erasable optical storage.

Delayed elastic effects in the glass ceramics Zerodur and ULE at room temperature.

PubMed

Pepi, J W; Golini, D

1991-08-01

The time-dependent phenomenon of delayed elasticity was studied at room temperature and is presented here for Zerodur and ULE. The effect is believed to be related to the alkali oxide content of the glass and to the rearrangement of the ion groups within the structure during stress.

Room temperature ferromagnetism of tin oxide nanocrystal based on synthesis methods

NASA Astrophysics Data System (ADS)

Sakthiraj, K.; Hema, M.; Balachandrakumar, K.

2016-04-01

The experimental conditions used in the preparation of nanocrystalline oxide materials play an important role in the room temperature ferromagnetism of the product. In the present work, a comparison was made between sol-gel, microwave assisted sol-gel and hydrothermal methods for preparing tin oxide nanocrystal. X-ray diffraction analysis indicates the formation of tetragonal rutile phase structure for all the samples. The crystallite size was estimated from the HRTEM images and it is around 6-12 nm. Using optical absorbance measurement, the band gap energy value of the samples has been calculated. It reveals the existence of quantum confinement effect in all the prepared samples. Photoluminescence (PL) spectra confirms that the luminescence process originates from the structural defects such as oxygen vacancies present in the samples. Room temperature hysteresis loop was clearly observed in M-H curve of all the samples. But the sol-gel derived sample shows the higher values of saturation magnetization (Ms) and remanence (Mr) than other two samples. This study reveals that the sol-gel method is superior to the other two methods for producing room temperature ferromagnetism in tin oxide nanocrystal.

A Stable Room-Temperature Luminescent Biphenylmethyl Radical.

PubMed

Ai, Xin; Chen, Yingxin; Feng, Yuting; Li, Feng

2018-03-05

There is only one family of room-temperature luminescent radicals, the triphenylmethyl radicals, to date. Herein, we synthesize a new stable room-temperature luminescent radical, (N-carbazolyl)bis(2,4,6-tirchlorophenyl)methyl radical (CzBTM), which has improved properties compared to the triphenylmethyl radicals. X-ray crystallography, electron paramagnetic resonance spectroscopy, and magnetic susceptibility measurements confirmed the radical structure. CzBTM shows room-temperature deep-red to near-infrared emission in various solutions. Both thermal and photo stability were significantly enhanced by the replacement of trichlorobenzene by the carbazole moiety. The electroluminescence results of CzBTM verify its potential application to circumvent the problem of triplet harvesting in traditional fluorescent OLEDs. A new family of stable luminescent radicals based on CzBTM is anticipated. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-quality RNA extracted from biopsied samples dehydrated and stored dried at room temperature without chemical preservation for up to 3 months as evidenced by RT-PCR results.

PubMed

Sadler, Theodore R; Khodavirdi, Ani C

2015-07-01

Handling and maintenance of biological tissues for nucleic acid and/or protein analysis has long been a challenge because of the perceived instability of these molecules at room temperature if not preserved or processed. Structural damage and compromised integrity of aforementioned biomolecules subsequent to preservation have also posed difficulties in their use in research. The development of technologies employing nonfixative methods with the capability to store at room temperature have been of growing interest. Our previous publication exploring preservation of proteins by desiccation challenged the convention of their unstable nature. Herein, we report the results of quantitative and qualitative analyses of RNA from tissue samples that were desiccated and stored at room temperature for up to 3 months. Our results indicate that viable RNA can be obtained from dehydrated ex vivo tissue samples that have been stored at room temperature.

Room-temperature processed tin oxide thin film as effective hole blocking layer for planar perovskite solar cells

NASA Astrophysics Data System (ADS)

Tao, Hong; Ma, Zhibin; Yang, Guang; Wang, Haoning; Long, Hao; Zhao, Hongyang; Qin, Pingli; Fang, Guojia

2018-03-01

Tin oxide (SnO2) film with high mobility and good transmittance has been reported as a promising semiconductor material for high performance perovskite solar cells (PSCs). In this study, ultrathin SnO2 film synthesized by radio frequency magnetron sputtering (RFMS) method at room temperature was employed as hole blocking layer for planar PSCs. The room-temperature sputtered SnO2 film not only shows favourable energy band structure but also improves the surface topography of fluorine doped SnO2 (FTO) substrate and perovskite (CH3NH3PbI3) layer. Thus, this SnO2 hole blocking layer can efficiently promote electron transport and suppress carrier recombination. Furthermore, the best efficiency of 13.68% was obtained for planar PSC with SnO2 hole blocking layer prepared at room temperature. This research highlights the room-temperature preparation process of hole blocking layer in PSC and has a certain reference significance for the usage of flexible and low-cost substrates.

On the temperature prediction in a fire escape passage

NASA Astrophysics Data System (ADS)

Casano, G.; Piva, S.

2017-11-01

Fire safety engineering requires a detailed understanding of fire behaviour and of its effects on structures and people. Many factors may condition the fire scenario, as for example, heat transfer between the flame and the boundary structures. Currently advanced numerical codes for the prediction of the fire behaviour are available. However, these solutions often require heavy calculations and long times. In this context analytical solutions can be useful for a fast analysis of simplified schematizations. After that, it is more effective the final utilization of the advanced fire codes. In this contribution, the temperature in a fire escape passage, separated with a thermally resistant wall from a fire room, is analysed. The escape space is included in a building where the neighbouring rooms are at a constant undisturbed temperature. The presence of the neighbouring rooms is considered with an equivalent heat transfer coefficient, in a boundary condition of the third type. An analytical solution is used to predict the temperature distribution during the fire. It allows to obtain useful information on the temperature reached in the escape area in contact with a burning room; it is useful also for a fast choice of the thermal characteristics of a firewall.

Large magnetoelectric coupling in magnetically short-range ordered Bi₅Ti₃FeO₁₅ film.

PubMed

Zhao, Hongyang; Kimura, Hideo; Cheng, Zhenxiang; Osada, Minoru; Wang, Jianli; Wang, Xiaolin; Dou, Shixue; Liu, Yan; Yu, Jianding; Matsumoto, Takao; Tohei, Tetsuya; Shibata, Naoya; Ikuhara, Yuichi

2014-06-11

Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi₅Ti₃FeO₁₅ with high ferroelectric Curie temperature of ~1000 K. Bi₅Ti₃FeO₁₅ thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mössbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic ordering at ~620 K. In Bi₅Ti₃FeO₁₅ with a stable ferroelectric order, the spin canting of magnetic-ion-based nanodomains via the Dzyaloshinskii-Moriya interaction might yield a robust magneto-electric coupling of ~400 mV/Oe·cm even at room temperature.

Tensile properties to 650 C and deformation structures in a precipitation strengthened titanium-aluminum alloy

NASA Technical Reports Server (NTRS)

Mendiratta, M. G.

1973-01-01

Appreciable strength levels were retained to 650 C in a Ti-10Al-1Si alloy aged in the (alpha + alpha sub 2) phase field to yield optimum room temperature strength and ductility. The aging treatment precipitated a uniform distribution of alpha sub 2-particles such that, at room temperature, dislocations bypassed instead of shearing the particles at low strains. Specimens fractured at room temperature exhibited fine uniform dimples even for those aging conditions that imparted no macroscopic ductility. The main crack appeared to propagate through the planar slip bands that had cut through the alpha sub 2-particles. A two-step aging process produced a higher volume fraction of bimodally distributed alpha sub 2-particles that led to higher strength levels at elevated temperatures. Both for the single size and the bimodal alpha sub 2-particle distributions, elevated-temperature deformation structures consisted mainly of planar slip bands that sheared through the alpha sub 2-particles.

Dynamically Switching the Polarization State of Light Based on the Phase Transition of Vanadium Dioxide

NASA Astrophysics Data System (ADS)

Jia, Zhi-Yong; Shu, Fang-Zhou; Gao, Ya-Jun; Cheng, Feng; Peng, Ru-Wen; Fan, Ren-Hao; Liu, Yongmin; Wang, Mu

2018-03-01

There have been great endeavors devoted to manipulating the polarization state of light by plasmonic nanostructures in recent decades. However, the topic of active polarizers has attracted much less attention. We present a composite plasmonic nanostructure consisting of vanadium dioxide that can dynamically modulate the polarization state of the reflected light through a thermally induced phase transition of vanadium dioxide. We design a system consisting of anisotropic plasmonic nanostructures with vanadium dioxide that exhibits distinct reflections subjected to different linearly polarized incidence at room temperature and in the heated state. Under a particular linearly polarized incidence, the polarization state of the reflected light changes at room temperature, and reverts to its original polarization state above the phase-transition temperature. The composite structure can also be used to realize a dynamically switchable infrared image, wherein a pattern can be visualized at room temperature while it disappears above the phase-transition temperature. The composite structure could be potentially used for versatile optical modulators, molecular detection, and polarimetric imaging.

Thermal Aging Study of a Dow Corning SE 1700 Porous Structure Made by Direct Ink Writing: 1-Year Results and Long-Term Predictions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Small, Ward; Pearson, Mark A.; Maiti, Amitesh

Dow Corning SE 1700 (reinforced polydimethylsiloxane) porous structures were made by direct ink writing (DIW). The specimens (~50% porosity) were subjected to various compressive strains (15, 30, 45%) and temperatures (room temperature, 35, 50, 70°C) in a nitrogen atmosphere (active purge) for 1 year. Compression set and load retention of the aged specimens were measured periodically during the study. Compression set increased with strain and temperature. After 1 year, specimens aged at room temperature, 35, and 50°C showed ~10% compression set (relative to the applied compressive deflection), while those aged at 70°C showed 20-40%. Due to the increasing compression set,more » load retention decreased with temperature, ranging from ~90% at room temperature to ~60-80% at 70°C. Long-term compression set and load retention at room temperature were predicted by applying time-temperature superposition (TTS). The predictions show compression set relative to the compressive deflection will be ~10-15% with ~70-90% load retention after 50 years at 15-45% strain, suggesting the material will continue to be mechanically functional. Comparison of the results to previously acquired data for cellular (M97*, M9760, M9763) and RTV (S5370) silicone foams suggests that the SE 1700 DIW porous specimens are on par with, or outperform, the legacy foams.« less

Structural and electrical characteristics of Bi2YTiVO9 ceramic

NASA Astrophysics Data System (ADS)

Gupta, Prabhasini; Padhee, Rajib; Mahapatra, P. K.; Choudhary, R. N. P.

2018-04-01

Studies of structural and electrical characteristics of a member of the Aurivillius structural family (Bi2YTiVO9), prepared by a standard ceramics technology, have been carried out. The phase-pure compound is found to crystallize in the orthorhombic crystal system. The dielectric constant remains around 200 in the studied frequency range of (1 kHz to 1 MHz) and in a temperature range from room temperature to 200 °C. The loss tangent remains in the range of 0.0236 to 0.0056 at room temperature and 0.081 to 0.009 at 200 °C in the same frequency range. The room temperature hysteresis loop exhibits the ferroelectric nature of the sample with remnant polarization of 0.025 μC/cm2 at the coercive field of 4.880 kV cm‑1. The experimental data obtained from Cole-Cole plot on static as well as infinitely high-frequency permittivity, relaxation time and relaxation distribution parameters are used to simulate ε‧, ε″and tanδ which match nicely with experimental data. The conductivity can be explained on the basis of Correlated Barrier Hopping (CBH) model. With 30.92% tenability and a figure of merit of 13 at room temperature and 1 kHz frequency, combined with a stable relative permittivity around 200 with a maximum variation of 6% over a temperature range of 200 °C and low loss tangent, the compound might have some tenability applications.

Correlation between structural, electrical and magnetic properties of GdMnO3 bulk ceramics

NASA Astrophysics Data System (ADS)

Samantaray, S.; Mishra, D. K.; Pradhan, S. K.; Mishra, P.; Sekhar, B. R.; Behera, Debdhyan; Rout, P. P.; Das, S. K.; Sahu, D. R.; Roul, B. K.

2013-08-01

This paper reports the effect of sintering temperature on ferroelectric properties of GdMnO3 (GMO) bulk ceramics at room temperature prepared by the conventional solid state reaction route following slow step sintering schedule. Ferroelectric hysteresis loop as well as sharp dielectric anomaly in pure (99.999%) GMO sintered ceramics has been clearly observed. Samples sintered at 1350 °C become orthorhombic with Pbnm space group and showed frequency independent sharp dielectric anomalies at 373 K and a square type of novel ferroelectric hysteresis loop was observed at room temperature. Interestingly, dielectric anomalies and ferroelectric behavior were observed to be dependent upon sintering temperature of GdMnO3. Room temperature dielectric constant (ɛr) value at different frequencies is observed to be abnormally high. The magnetic field and temperature dependent magnetization show antiferromagnetic behavior at 40 K for both 1350 °C and 1700 °C sintered GMO. Present findings showed the possibility of application of GdMnO3 at room temperature as multifunctional materials.

Mossbauer Study of Low Temperature Magnetic and magnetooptic Properties of Amorphous Tb/Fe Multilayers

NASA Astrophysics Data System (ADS)

Chowdhury, Ataur

Magnetic and magnetooptic properties of multilayers critically depend on detailed magnetic and structural ordering of the interface. To study these properties in Tb/Fe multilayers, samples with varying layer thicknesses were fabricated by planar magnetic sputtering on polyester substrates. Mossbauer effect spectra were recorded at different temperatures ranging between 20 K and 300 K. The results show that perpendicular magnetic anisotropy (PMA) increases as temperature decreases for samples that show parallel anisotropy at room temperature, and for samples that show strong PMA at room temperature, no significant change in PMA is observed at low temperature (<100 K). Hyperfine field of samples that display parallel anisotropy at room temperature shows oscillatory behavior, reminiscent of RKKY oscillations, at low temperatures (<100 K). Plausible causes of these properties will be discussed in the paper.

Nickel aluminide alloy suitable for structural applications

DOEpatents

Liu, C.T.

1998-03-10

Alloys are disclosed for use in structural applications based upon NiAl to which are added selected elements to enhance room temperature ductility and high temperature strength. Specifically, small additions of molybdenum produce a beneficial alloy, while further additions of boron, carbon, iron, niobium, tantalum, zirconium and hafnium further improve performance of alloys at both room temperature and high temperatures. A preferred alloy system composition is Ni--(49.1{+-}0.8%)Al--(1.0{+-}0.8%)Mo--(0.7 + 0.5%)Nb/Ta/Zr/Hf--(nearly zero to 0.03%)B/C, where the % is at. % in each of the concentrations. All alloys demonstrated good oxidation resistance at the elevated temperatures. The alloys can be fabricated into components using conventional techniques. 4 figs.

Size effect on the structural, magnetic, and magnetotransport properties of electron doped manganite La0.15Ca0.85MnO3

NASA Astrophysics Data System (ADS)

Thomas, Rini; Das, Gangadhar; Mondal, Rajib; Pradheesh, R.; Mahato, R. N.; Geetha Kumary, T.; Nirmala, R.; Morozkin, A. V.; Lamsal, J.; Yelon, W. B.; Nigam, A. K.; Malik, S. K.

2012-04-01

Nanocrystalline La0.15Ca0.85MnO3 samples of various grain sizes ranging from ˜17 to 42 nm have been prepared by sol-gel technique. Phase purity and composition were verified by room temperature x-ray diffraction and SEM-EDAX analysis. The bulk La0.15Ca0.85MnO3 is known to order antiferromagnetically around 170 K and to undergo a simultaneous crystal structural transition. DC magnetization measurements on 17 nm size La0.15Ca0.85MnO3 show a peak at ˜130 K (TN) in zero-field-cooled (ZFC) state. Field-cooled magnetization bifurcates from ZFC data around 200 K hinting a weak ferromagnetic component near room temperature due to surface moments of the nanoparticle sample. Low temperature powder neutron diffraction experiments reveal that the incomplete structural transition from room temperature orthorhombic to low temperature orthorhombic-monoclinic state also occurs in the nanoparticle sample as in the bulk. Magnetization in the ordered state decreases as particle size increases, thus indicating the reduction of the competing ferromagnetic surface moments.

Over 7% magnetic field-induced strain in a Ni-Mn-Ga five-layered martensite

NASA Astrophysics Data System (ADS)

Pagounis, E.; Chulist, R.; Szczerba, M. J.; Laufenberg, M.

2014-08-01

A Ni-Mn-Ga single crystal with a modulated five-layered martensite structure is reported, demonstrating giant magnetic field induced strain (MFIS) of 7.1% at room temperature and of 6% at temperatures close to the austenite transformation (TA = 71 °C). The room temperature MFIS clearly exceeds the best results of around 6% measured earlier in 10M martensites. The larger MFIS is connected to the huge (>1%) change in the lattice distortion of the 10M structure, obtained within a narrow temperature interval of 47 K, which has been previously observed only during intermartensitic transformation. The present material shall effectively reduce the size of magnetic shape memory actuators.

Rapid and high throughput fabrication of high temperature stable structures through PDMS transfer printing

NASA Astrophysics Data System (ADS)

Hohenberger, Erik; Freitag, Nathan; Korampally, Venumadhav

2017-07-01

We report on a facile and low cost fabrication approach for structures—gratings and enclosed nanochannels, through simple solution processed chemistries in conjunction with nanotransfer printing techniques. The ink formulation primarily consisting of an organosilicate polymeric network with a small percentage of added 3-aminopropyl triethoxysilane crosslinker allows one to obtain robust structures that are not only stable towards high temperature processing steps as high as 550 °C but also exhibit exceptional stability against a host of organic solvent washes. No discernable structure distortion was observed compared to the as-printed structures (room temperature processed) when printed structures were subjected to temperatures as high as 550 °C. We further demonstrate the applicability of this technique towards the fabrication of more complex nanostructures such as enclosed channels through a double transfer method, leveraging the exceptional room temperature cross-linking ability of the printed structures and their subsequent resistance to dissolution in organic solvent washes. The exceptional temperature and physico-chemical stability of the nanotransfer printed structures makes this a useful fabrication tool that may be applied as is, or integrated with conventional lithographic techniques for the large area fabrication of functional nanostructures and devices.

Rietveld refined structural and room temperature vibrational properties of BaTiO3 doped La0.67Ba0.33MnO3 composites

NASA Astrophysics Data System (ADS)

Dar, M. A.; Sheikh, M. W.; Malla, M. S.; Varshney, Dinesh

2016-05-01

The composites of (1-x) La0.67Ba0.33MnO3 (LBMO) + xBaTiO3 (BTO) (x = 0, 0.25 and 1.0) were synthesized by conventional solid-state reaction method. Rietveld refinement was employed to characterize the structural information of the prepared ceramics. The result of the Rietveld refinement of X-ray powder diffraction of La0.67Ba0.33MnO3 and BaTiO3 shows that these compounds crystallize in rhombohedral (R3c) and tetragonal (P4mm), respectively. The structural parameters and the reliability factors for the LBMO-BTO composite ceramics were successfully determined by the Rietveld refinement. At room temperature, Raman active phonon modes predicted by the group theory were observed only in BaTiO3 and composite sample. Pure LBMO does not show any Raman active Phonon mode at room temperature.

Room-temperature wide-range luminescence and structural, optical, and electrical properties of SILAR deposited Cu-Zn-S nano-structured thin films

NASA Astrophysics Data System (ADS)

Jose, Edwin; Kumar, M. C. Santhosh

2016-09-01

We report the deposition of nanostructured Cu-Zn-S composite thin films by Successive Ionic Layer Adsorption and Reaction (SILAR) method on glass substrates at room temperature. The structural, morphological, optical, photoluminescence and electrical properties of Cu-Zn-S thin films are investigated. The results of X-ray diffraction (XRD) and Raman spectroscopy studies indicate that the films exhibit a ternary Cu-Zn-S structure rather than the Cu xS and ZnS binary composite. Scanning electron microscope (SEM) studies show that the Cu-Zn-S films are covered well over glass substrates. The optical band gap energies of the Cu-Zn-S films are calculated using UV-visible absorption measurements, which are found in the range of 2.2 to 2.32 eV. The room temperature photoluminescence studies show a wide range of emissions from 410 nm to 565 nm. These emissions are mainly due to defects and vacancies in the composite system. The electrical studies using Hall effect measurements show that the Cu-Zn-S films are having p-type conductivity.

Ultrasonic acoustic levitation for fast frame rate X-ray protein crystallography at room temperature.

PubMed

Tsujino, Soichiro; Tomizaki, Takashi

2016-05-06

Increasing the data acquisition rate of X-ray diffraction images for macromolecular crystals at room temperature at synchrotrons has the potential to significantly accelerate both structural analysis of biomolecules and structure-based drug developments. Using lysozyme model crystals, we demonstrated the rapid acquisition of X-ray diffraction datasets by combining a high frame rate pixel array detector with ultrasonic acoustic levitation of protein crystals in liquid droplets. The rapid spinning of the crystal within a levitating droplet ensured an efficient sampling of the reciprocal space. The datasets were processed with a program suite developed for serial femtosecond crystallography (SFX). The structure, which was solved by molecular replacement, was found to be identical to the structure obtained by the conventional oscillation method for up to a 1.8-Å resolution limit. In particular, the absence of protein crystal damage resulting from the acoustic levitation was carefully established. These results represent a key step towards a fully automated sample handling and measurement pipeline, which has promising prospects for a high acquisition rate and high sample efficiency for room temperature X-ray crystallography.

Ultrasonic acoustic levitation for fast frame rate X-ray protein crystallography at room temperature

NASA Astrophysics Data System (ADS)

Tsujino, Soichiro; Tomizaki, Takashi

2016-05-01

Increasing the data acquisition rate of X-ray diffraction images for macromolecular crystals at room temperature at synchrotrons has the potential to significantly accelerate both structural analysis of biomolecules and structure-based drug developments. Using lysozyme model crystals, we demonstrated the rapid acquisition of X-ray diffraction datasets by combining a high frame rate pixel array detector with ultrasonic acoustic levitation of protein crystals in liquid droplets. The rapid spinning of the crystal within a levitating droplet ensured an efficient sampling of the reciprocal space. The datasets were processed with a program suite developed for serial femtosecond crystallography (SFX). The structure, which was solved by molecular replacement, was found to be identical to the structure obtained by the conventional oscillation method for up to a 1.8-Å resolution limit. In particular, the absence of protein crystal damage resulting from the acoustic levitation was carefully established. These results represent a key step towards a fully automated sample handling and measurement pipeline, which has promising prospects for a high acquisition rate and high sample efficiency for room temperature X-ray crystallography.

Ultrasonic acoustic levitation for fast frame rate X-ray protein crystallography at room temperature

PubMed Central

Tsujino, Soichiro; Tomizaki, Takashi

2016-01-01

Increasing the data acquisition rate of X-ray diffraction images for macromolecular crystals at room temperature at synchrotrons has the potential to significantly accelerate both structural analysis of biomolecules and structure-based drug developments. Using lysozyme model crystals, we demonstrated the rapid acquisition of X-ray diffraction datasets by combining a high frame rate pixel array detector with ultrasonic acoustic levitation of protein crystals in liquid droplets. The rapid spinning of the crystal within a levitating droplet ensured an efficient sampling of the reciprocal space. The datasets were processed with a program suite developed for serial femtosecond crystallography (SFX). The structure, which was solved by molecular replacement, was found to be identical to the structure obtained by the conventional oscillation method for up to a 1.8-Å resolution limit. In particular, the absence of protein crystal damage resulting from the acoustic levitation was carefully established. These results represent a key step towards a fully automated sample handling and measurement pipeline, which has promising prospects for a high acquisition rate and high sample efficiency for room temperature X-ray crystallography. PMID:27150272

Evaluation of Ceramic Honeycomb Core Compression Behavior at Room Temperature

NASA Technical Reports Server (NTRS)

Bird, Richard K.; Lapointe, Thomas S.

2013-01-01

Room temperature flatwise compression tests were conducted on two varieties of ceramic honeycomb core specimens that have potential for high-temperature structural applications. One set of specimens was fabricated using strips of a commercially-available thin-gage "ceramic paper" sheet molded into a hexagonal core configuration. The other set was fabricated by machining honeycomb core directly from a commercially available rigid insulation tile material. This paper summarizes the results from these tests.

High-performance single nanowire tunnel diodes.

PubMed

Wallentin, Jesper; Persson, Johan M; Wagner, Jakob B; Samuelson, Lars; Deppert, Knut; Borgström, Magnus T

2010-03-10

We demonstrate single nanowire tunnel diodes with room temperature peak current densities of up to 329 A/cm(2). Despite the large surface to volume ratio of the type-II InP-GaAs axial heterostructure nanowires, we measure peak to valley current ratios (PVCR) of up to 8.2 at room temperature and 27.6 at liquid helium temperature. These sub-100-nm-diameter structures are promising components for solar cells as well as electronic applications.

Effect of sintering on optical, structural and photoluminescence properties of ZnO thin films prepared by sol-gel process.

PubMed

Vishwas, M; Narasimha Rao, K; Arjuna Gowda, K V; Chakradhar, R P S

2010-09-15

Zinc oxide (ZnO) thin films have been deposited on glass substrates via sol-gel technique using zinc acetate dihydrate as precursor by spin coating of the sol at 2000 rpm. Effects of annealing temperature on optical, structural and photo luminescence properties of the deposited ZnO films have been investigated. The phase transition from amorphous to polycrystalline hexagonal wurtzite structure was observed at an annealing temperature of 400 degrees C. An average transmittance of 87% in the visible region has been obtained at room temperature. The optical transmittance has slightly increased with increase of annealing temperature. The band gap energy was estimated by Tauc's method and found to be 3.22 eV at room temperature. The optical band gap energy has decreased with increasing annealing temperature. The photoluminescence (PL) intensity increased with annealing temperature up to 200 degrees C and decreased at 300 degrees C. Copyright 2010 Elsevier B.V. All rights reserved.

Aging of ceramic carbonized hydroxyapatite at room temperature

NASA Astrophysics Data System (ADS)

Tkachenko, M. V.; Kamzin, A. S.

2016-08-01

The process of aging of ceramic carbonized hydroxyapatite (CHA) produced in a dry carbon dioxide atmosphere at temperatures of 800-1200°C has been studied by chemical and X-ray structural analysis, infrared spectroscopy, and scanning electron microscopy methods. The phase composition and structure of initial prepared ceramics samples and those aged for a year have been compared. It has been shown that relaxation of internal stresses occurring during pressed sample sintering causes plastic deformation of crystallites at room temperature, accompanied by redistribution of carbonate ions between A1, A2, B1, and B2 sites and CHA decomposition with the formation of CaO separations.

Cryo-cooling in macromolecular crystallography: advantages, disadvantages and optimization.

PubMed

Juers, Douglas H; Matthews, Brian W

2004-05-01

The flash-cooling of crystals in macromolecular crystallography has become commonplace. The procedure makes it possible to collect data from much smaller specimens than was the case in the past Also, flash-cooled crystals are much less prone to radiation damage than their room-temperature counterparts, allowing data to be accumulated over extended periods of time. Notwithstanding the attractiveness of the technique, it does have potential disadvantages. First, better methods need to be developed to prevent damage to crystals on freezing. There is also a risk that structures determined at low temperature may suggest conclusions based on aspects of the structure that are not necessarily relevant at room temperature.

Crystal induced phosphorescence from Benz(a)anthracene microcrystals at room temperature

NASA Astrophysics Data System (ADS)

Maity, Samir; Mazumdar, Prativa; Shyamal, Milan; Sahoo, Gobinda Prasad; Misra, Ajay

2016-03-01

Pure organic compounds that are also phosphorescent at room temperature are very rare in literature. Here, we report efficient phosphorescence emission from aggregated hydrosol of Benz(a)anthracene (BaA) at room temperature. Aggregated hydrosol of BaA has been synthesized by re-precipitation method and SDS is used as morphology directing agent. Morphology of the particles is characterized using optical and scanning electronic microcopy (SEM). Photophysical properties of the aggregated hydrosol are carried out using UV-vis, steady state and time resolved fluorescence study. The large stoke shifted structured emission from aggregated hydrosol of BaA has been explained due to phosphorescence emission of BaA at room temperature. In the crystalline state, the restricted intermolecular motions (RIM) such as rotations and vibrations are activated by crystal lattice. This rigidification effect makes the chromophore phosphorescent at room temperature. The possible stacking arrangement of the neighboring BaA within the aggregates has been substantiated by computing second order Fukui parameter as local reactivity descriptors. Computational study also reveals that the neighboring BaA molecules are present in parallel slipped conformation in its aggregated crystalline form.

Above room temperature ferromagnetism in Si:Mn and TiO(2-delta)Co.

PubMed

Granovsky, A; Orlov, A; Perov, N; Gan'shina, E; Semisalova, A; Balagurov, L; Kulemanov, I; Sapelkin, A; Rogalev, A; Smekhova, A

2012-09-01

We present recent experimental results on the structural, electrical, magnetic, and magneto-optical properties of Mn-implanted Si and Co-doped TiO(2-delta) magnetic oxides. Si wafers, both n- and p-type, with high and low resistivity, were used as the starting materials for implantation with Mn ions at the fluencies up to 5 x 10(16) cm(-2). The saturation magnetization was found to show the lack of any regular dependence on the Si conductivity type, type of impurity and the short post-implantation annealing. According to XMCD Mn impurity in Si does not bear any appreciable magnetic moment at room temperature. The obtained results indicate that above room temperature ferromagnetism in Mn-implanted Si originates not from Mn impurity but rather from structural defects in Si. The TiO(2-delta):Co thin films were deposited on LaAlO3 (001) substrates by magnetron sputtering in the argon-oxygen atmosphere at oxygen partial pressure of 2 x 10(-6)-2 x 10(-4) Torr. The obtained transverse Kerr effect spectra at the visible and XMCD spectra indicate on intrinsic room temperature ferromagnetism in TiO(2-delta):Co thin films at low (< 1%) volume fraction of Co.

Stable room-temperature ferromagnetic phase at the FeRh(100) surface

DOE PAGES

Pressacco, Federico; Uhlir, Vojtech; Gatti, Matteo; ...

2016-03-03

Interfaces and low dimensionality are sources of strong modifications of electronic, structural, and magnetic properties of materials. FeRh alloys are an excellent example because of the first-order phase transition taking place at ~400 K from an antiferromagnetic phase at room temperature to a high temperature ferromagnetic one. It is accompanied by a resistance change and volume expansion of about 1%. We have investigated the electronic and magnetic properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies characterized by different probing depths, namely X-ray magnetic circular dichroism and photoelectron spectroscopy. Furthermore, we find that the symmetry breaking induced at themore » Rh-terminated surface stabilizes a surface ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally antiferromagnetic phase at room temperature. First-principles calculations provide a microscopic description of the structural relaxation and the electron spin-density distribution that support the experimental findings.« less

Defect types and room-temperature ferromagnetism in undoped rutile TiO2 single crystals

NASA Astrophysics Data System (ADS)

Li, Dong-Xiang; Qin, Xiu-Bo; Zheng, Li-Rong; Li, Yu-Xiao; Cao, Xing-Zhong; Li, Zhuo-Xin; Yang, Jing; Wang, Bao-Yi

2013-03-01

Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane. By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy, Ti3+—VO defect complexes (or clusters) have been identified in annealed crystals at a high vacuum. We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism. In addition, excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.

The structural properties of InGaN alloys and the interdependence on the thermoelectric behavior

NASA Astrophysics Data System (ADS)

Kucukgok, Bahadir; Wu, Xuewang; Wang, Xiaojia; Liu, Zhiqiang; Ferguson, Ian T.; Lu, Na

2016-02-01

The III-Nitrides are promising candidate for high efficiency thermoelectric (TE) materials and devices due to their unique features which includes high thermal stability. A systematic study of the room temperature TE properties of metalorganic chemical vapor deposition grown InxGa1-xN were investigated for x = 0.07 to 0.24. This paper investigated the role of indium composition on the TE properties of InGaN alloys in particular the structural properties for homogenous material that did not show significant phase separation. The highest Seebeck and power factor values of 507 μV K-1 and 21.84 × 10-4 Wm-1K-1 were observed, respectively for In0.07Ga0.93N at room temperature. The highest value of figure-of-merit (ZT) was calculated to be 0.072 for In0.20Ga0.80N alloy at room temperature.

Room-Temperature-Cured Copolymers for Lithium Battery Gel Electrolytes

NASA Technical Reports Server (NTRS)

Meador, Mary Ann B.; Tigelaar, Dean M.

2009-01-01

Polyimide-PEO copolymers (PEO signifies polyethylene oxide) that have branched rod-coil molecular structures and that can be cured into film form at room temperature have been invented for use as gel electrolytes for lithium-ion electric-power cells. These copolymers offer an alternative to previously patented branched rod-coil polyimides that have been considered for use as polymer electrolytes and that must be cured at a temperature of 200 C. In order to obtain sufficient conductivity for lithium ions in practical applications at and below room temperature, it is necessary to imbibe such a polymer with a suitable carbonate solvent or ionic liquid, but the high-temperature cure makes it impossible to incorporate and retain such a liquid within the polymer molecular framework. By eliminating the high-temperature cure, the present invention makes it possible to incorporate the required liquid.

Spectroscopy of Single Free Standing Quantum Wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, M D; Hollars, C W; Huser, T

2006-03-14

We investigated the interaction of quantum confined exciton states GaAs quantum wells with native surface states. Single molecule photoluminescence (PL) spectroscopy, developed by T. Huser at LLNL was used to probe the unique bare quantum wells in the free standing quantum well structure. The latter was developed by the M. D. Williams at Clark Atlanta University. The goals of the project during this budget cycle were to procure samples containing GaAs free standing QWs, identify suitable regions for PL analysis at Lawrence Livermore, analyze the structures at room temperature and at liquid nitrogen temperatures. The specific regions of interest onmore » the sample structures were identified by scanning electron microscopy at Clark Atlanta prior to transport to LLNL. Previous attempts at other facilities using NSOM, cathodoluminescence, and conventional PL showed little luminescence activity at room temperature from the 200 {angstrom} thick wells. This suggested either excess recombination due to surface states in the quantum well region or insufficient absorption length for photoluminescence. The literature suggested that the effect of the defects could be eliminated by reducing the sample temperature below their associated activation energies. In our previous subcontract work with LLNL, a significant amount of effort was expended to modify the apparatus to allow low temperature measurements. The modifications were not successful and we concluded that in order to do the measurements at low temperature we would need to purchase a commercial optical cryostat to get reliable results. Ms. Rochelle Bryant worked during the summer as an intern at LLNL on the project under the supervision of C. Hollars and in collaboration with T. Huser and found that PL emission could be obtained at room temperature. This was a surprising result as the literature and our experience shows that there is no PL emission from GaAs at room temperature. We speculate that this is due to the small interaction region excited by the laser source. We proceeded with the project using this new found room temperature capability and have analyzed the effect of various chemical species on the PL emission from the GaAs QWs. We were able to observe some significant intensity modifications of the PL spectra with chemical adsorbants. This progress holds promise for the development of this structure as a chemical or biological sensor.« less

Low void content autoclave molded titanium alloy and polyimide graphite composite structures.

NASA Technical Reports Server (NTRS)

Vaughan, R. W.; Jones, R. J.; Creedon, J. F.

1972-01-01

This paper discusses a resin developed for use in autoclave molding of polyimide graphite composite stiffened, titanium alloy structures. Both primary and secondary bonded structures were evaluated that were produced by autoclave processing. Details of composite processing, adhesive formulary, and bonding processes are provided in this paper, together with mechanical property data for structures. These data include -65 F, room temperature, and 600 F shear strengths; strength retention after aging; and stress rupture properties at 600 F under various stress levels for up to 1000 hours duration. Typically, shear strengths in excess of 16 ksi at room temperature with over 60% strength retention at 600 F were obtained with titanium alloy substrates.

Multiferroic GaN nanofilms grown within Na-4 mica channels

NASA Astrophysics Data System (ADS)

Bhattacharya, Santanu; Datta, A.; Chakravorty, D.

2010-03-01

Gallium nitride nanofilms grown within nanochannels of Na-4 mica structure, exhibit ferromagnetism even at room temperature due to the presence of gallium vacancies at the surfaces of the nanofilms. These nanofilms also show a ferroelectric behavior at room temperature ascribed to a small distortion in the crystal structure of GaN due to its growth within the Na-4 mica nanochannels. A colossal increase in 338% in dielectric constant was observed for an applied magnetic field of 26 kOe. The magnetoelectric effect is ascribed to magnetostriction of magnetic GaN phase.

An acoustic on-chip goniometer for room temperature macromolecular crystallography.

PubMed

Burton, C G; Axford, D; Edwards, A M J; Gildea, R J; Morris, R H; Newton, M I; Orville, A M; Prince, M; Topham, P D; Docker, P T

2017-12-05

This paper describes the design, development and successful use of an on-chip goniometer for room-temperature macromolecular crystallography via acoustically induced rotations. We present for the first time a low cost, rate-tunable, acoustic actuator for gradual in-fluid sample reorientation about varying axes and its utilisation for protein structure determination on a synchrotron beamline. The device enables the efficient collection of diffraction data via a rotation method from a sample within a surface confined droplet. This method facilitates efficient macromolecular structural data acquisition in fluid environments for dynamical studies.

Dense nanocrystalline yttrium iron garnet films formed at room temperature by aerosol deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Scooter D., E-mail: scooter.johnson@nrl.navy.mil; Glaser, Evan R.; Cheng, Shu-Fan

Highlights: • We deposit yttrium iron garnet films at room temperature using aerosol deposition. • Films are 96% of theoretical density for yttrium iron garnet. • We report magnetic and structural properties post-deposition and post-annealing. • Low-temperature annealing decreases the FMR linewidth. • We discuss features of the FMR spectra at each anneal temperature. - Abstract: We have employed aerosol deposition to form polycrystalline yttrium iron garnet (YIG) films on sapphire at room temperature that are 90–96% dense. We characterize the structural and dynamic magnetic properties of the dense films using scanning electron microscopy, X-ray diffraction, and ferromagnetic resonance techniques.more » We find that the as-deposited films are pure single-phase YIG formed of compact polycrystallites ∼20 nm in size. The ferromagnetic resonance mode occurs at 2829 G with a linewidth of 308 G. We perform a series of successive anneals up to 1000 °C on a film to explore heat treatment on the ferromagnetic resonance linewidth. We find the narrowest linewidth of 98 G occurs after a 750 °C anneal.« less

Advances in processing of NiAl intermetallic alloys and composites for high temperature aerospace applications

NASA Astrophysics Data System (ADS)

Bochenek, Kamil; Basista, Michal

2015-11-01

Over the last few decades intermetallic compounds such as NiAl have been considered as potential high temperature structural materials for aerospace industry. A large number of investigations have been reported describing complex fabrication routes, introducing various reinforcing/alloying elements along with theoretical analyses. These research works were mainly focused on the overcoming of main disadvantage of nickel aluminides that still restricts their application range, i.e. brittleness at room temperature. In this paper we present an overview of research on NiAl processing and indicate methods that are promising in solving the low fracture toughness issue at room temperature. Other material properties relevant for high temperature applications are also addressed. The analysis is primarily done from the perspective of NiAl application in aero engines in temperature regimes from room up to the operating temperature (over 1150 °C) of turbine blades.

Preliminary neutron and X-ray crystallographic studies of equine cyanomethemoglobin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovalevsky, A.Y.; Fisher, S.Z.; Seaver, S.

2010-08-18

Room-temperature and 100 K X-ray and room-temperature neutron diffraction data have been measured from equine cyanomethemoglobin to 1.7 {angstrom} resolution using a home source, to 1.6 {angstrom} resolution on NE-CAT at the Advanced Photon Source and to 2.0 {angstrom} resolution on the PCS at Los Alamos Neutron Science Center, respectively. The cyanomethemoglobin is in the R state and preliminary room-temperature electron and neutron scattering density maps clearly show the protonation states of potential Bohr groups. Interestingly, a water molecule that is in the vicinity of the heme group and coordinated to the distal histidine appears to be expelled from thismore » site in the low-temperature structure.« less

Shell structures in aluminum nanocontacts at elevated temperatures

PubMed Central

2012-01-01

Aluminum nanocontact conductance histograms are studied experimentally from room temperature up to near the bulk melting point. The dominant stable configurations for this metal show a very early crossover from shell structures at low wire diameters to ionic subshell structures at larger diameters. At these larger radii, the favorable structures are temperature-independent and consistent with those expected for ionic subshell (faceted) formations in face-centered cubic geometries. When approaching the bulk melting temperature, these local stability structures become less pronounced as shown by the vanishing conductance histogram peak structure. PMID:22325572

Serial femtosecond X-ray diffraction of enveloped virus microcrystals

DOE PAGES

Lawrence, Robert M.; Conrad, Chelsie E.; Zatsepin, Nadia A.; ...

2015-08-20

Serial femtosecond crystallography (SFX) using X-ray free-electron lasers has produced high-resolution, room temperature, time-resolved protein structures. We report preliminary SFX of Sindbis virus, an enveloped icosahedral RNA virus with ~700 Å diameter. Microcrystals delivered in viscous agarose medium diffracted to ~40 Å resolution. Small-angle diffuse X-ray scattering overlaid Bragg peaks and analysis suggests this results from molecular transforms of individual particles. Viral proteins undergo structural changes during entry and infection, which could, in principle, be studied with SFX. This is a pertinent step toward determining room temperature structures from virus microcrystals that may enable time-resolved studies of enveloped viruses.

Phase-coexistence and thermal hysteresis in samples comprising adventitiously doped MnAs nanocrystals: programming of aggregate properties in magnetostructural nanomaterials.

PubMed

Zhang, Yanhua; Regmi, Rajesh; Liu, Yi; Lawes, Gavin; Brock, Stephanie L

2014-07-22

Small changes in the synthesis of MnAs nanoparticles lead to materials with distinct behavior. Samples prepared by slow heating to 523 K (type-A) exhibit the characteristic magnetostructural transition from the ferromagnetic hexagonal (α) to the paramagnetic orthorhombic (β) phase of bulk MnAs at Tp = 312 K, whereas those prepared by rapid nucleation at 603 K (type-B) adopt the β structure at room temperature and exhibit anomalous magnetic properties. The behavior of type-B nanoparticles is due to P-incorporation (up to 3%), attributed to reaction of the solvent (trioctylphosphine oxide). P-incorporation results in a decrease in the unit cell volume (∼1%) and shifts Tp below room temperature. Temperature-dependent X-ray diffraction reveals a large region of phase-coexistence, up to 90 K, which may reflect small differences in Tp from particle-to-particle within the nearly monodisperse sample. The large coexistence range coupled to the thermal hysteresis results in process-dependent phase mixtures. As-prepared type-B samples exhibiting the β structure at room temperature convert to a mixture of α and β after the sample has been cooled to 77 K and rewarmed to room temperature. This change is reflected in the magnetic response, which shows an increased moment and a shift in the temperature hysteresis loop after cooling. The proportion of α present at room temperature can also be augmented by application of an external magnetic field. Both doped (type-B) and undoped (type-A) MnAs nanoparticles show significant thermal hysteresis narrowing relative to their bulk phases, suggesting that formation of nanoparticles may be an effective method to reduce thermal losses in magnetic refrigeration applications.

Low temperature structures of dCpG-proflavine. Conformational and hydration effects.

PubMed Central

Schneider, B; Ginell, S L; Berman, H M

1992-01-01

The structure of the complex of dCpG with proflavine was determined using x-ray data taken at -130 degrees C (low temperature) and at -2 degrees C (cold temperature) and compared with the structure of the complex determined previously at room temperature (Shieh, H. S., H. M. Berman, M. Dabrow, and S. Neidle. 1980. Nucleic Acids Res. 8:85-97). Low temperature was refined with 5,125 reflections between 8.0 and 0.93 A, Anisotropically modeled temperature factors were used for DNA/drug atoms and isotropic ones for water oxygens to R factor of 12.2% in P2(1)2(1)2; a = 32.853, b = 21.760, c = 13.296 A. Cold temperature was refined isotropically with 2,846 reflections 8.0-0.89 A to R = 15.1% in P2(1)2(1)2; a = 32.867, b = 22.356, c = 13.461 A. Both structures are very similar to the room temperature one, though some important differences were observed: one guanine sugar moiety is disordered and additional water molecules have been located that give rise to infinite polyhedral hydration networks. Images FIGURE 2 PMID:1489914

Low temperature structures of dCpG-proflavine.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schneider, B.; Ginell, S. L.; Berman, H. M.

1992-12-01

The structure of the complex of dCpG with proflavine was determined using x-ray data taken at -130 degrees C (low temperature) and at -2 degrees C (cold temperature) and compared with the structure of the complex determined previously at room temperature (Shieh, H. S., H. M. Berman, M. Dabrow, and S. Neidle. 1980. Nucleic Acids Res. 8:85-97). Low temperature was refined with 5,125 reflections between 8.0 and 0.93 A, Anisotropically modeled temperature factors were used for DNA/drug atoms and isotropic ones for water oxygens to R factor of 12.2% in P2(1)2(1)2; a = 32.853, b = 21.760, c = 13.296more » A. Cold temperature was refined isotropically with 2,846 reflections 8.0-0.89 A to R = 15.1% in P2(1)2(1)2; a = 32.867, b = 22.356, c = 13.461 A. Both structures are very similar to the room temperature one, though some important differences were observed: one guanine sugar moiety is disordered and additional water molecules have been located that give rise to infinite polyhedral hydration networks.« less

Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys

NASA Astrophysics Data System (ADS)

Jin, Y.; Kharel, P.; Lukashev, P.; Valloppilly, S.; Staten, B.; Herran, J.; Tutic, I.; Mitrakumar, M.; Bhusal, B.; O'Connell, A.; Yang, K.; Huh, Y.; Skomski, R.; Sellmyer, D. J.

2016-08-01

The structural, electronic, and magnetic properties of CoFeCrX (X = Si, Ge) Heusler alloys have been investigated. Experimentally, the alloys were synthesized in the cubic L21 structure with small disorder. The cubic phase of CoFeCrSi was found to be highly stable against heat treatment, but CoFeCrGe disintegrated into other new compounds when the temperature reached 402 °C (675 K). Although the first-principle calculation predicted the possibility of tetragonal phase in CoFeCrGe, the tetragonal phase could not be stabilized experimentally. Both CoFeCrSi and CoFeCrGe compounds showed ferrimagnetic spin order at room temperature and have Curie temperatures (TC) significantly above room temperature. The measured TC for CoFeCrSi is 790 K but that of CoFeCrGe could not be measured due to its dissociation into new compounds at 675 K. The saturation magnetizations of CoFeCrSi and CoFeCrGe are 2.82 μB/f.u. and 2.78 μB/f.u., respectively, which are close to the theoretically predicted value of 3 μB/f.u. for their half-metallic phases. The calculated band gaps for CoFeCrSi and CoFeCrGe are, respectively, 1 eV and 0.5 eV. These materials have potential for spintronic device applications, as they exhibit half-metallic electronic structures with large band gaps, and Curie temperatures significantly above room temperature.

Room Temperature Monoclinic Phase in BaTiO3 Single Crystals

NASA Astrophysics Data System (ADS)

Denev, Sava; Kumar, Amit; Barnes, Andrew; Vlahos, Eftihia; Shepard, Gabriella; Gopalan, Venkatraman

2010-03-01

BaTiO3 is a well studied ferroelectric material for the last half century. It is well known to show phase transitions to tetragonal, orthorhombic and rhombohedral phases upon cooling. Yet, some old and some recent studies have argued that all these phases co-exist with a second phase with monoclinic distortion. Using optical second harmonic generation (SHG) at room temperature we directly present evidence for such monoclininc phase co-existing with tetragonal phase at room temperature. We observe domains with the expected tetragonal symmetry exhibiting 90^o and 180^o domain walls. However, at points of higher stress at the tips of the interpenetrating tetragonal domains we observe a well pronounced metastable ``staircase pattern'' with a micron-scale fine structure. Polarization studies show that this phase can be explained only by monoclinic symmetry. This phase is very sensitive to external perturbations such as temperature and fields, hence stabilizing this phase at room temperature could lead to large properties' tunability.

A Polar Corundum Oxide Displaying Weak Ferromagnetism at Room Temperature

PubMed Central

2012-01-01

Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO3 (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO3 has a weak ferromagnetic ground state below 356 K—this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO3. PMID:22280499

Soft x-ray resonant diffraction study of magnetic structure in magnetoelectric Y-type hexaferrite

NASA Astrophysics Data System (ADS)

Ueda, H.; Tanaka, Y.; Wakabayashi, Y.; Kimura, T.

2018-05-01

The effect of magnetic field on the magnetic structure associated with magnetoelectric properties in a Y-type hexaferrite, Ba1.3Sr0.7CoZnFe11AlO22, was investigated by utilizing the soft x-ray resonant diffraction technique. In this hexaferrite, the so-called alternating longitudinal conical phase is stabilized at room temperature and zero magnetic field. Below room temperature, however, this phase is transformed into the so-called transverse conical phase by applying an in-plane magnetic field (≈ 0.3 T). The transverse conical phase persists even after removing the magnetic field. The magnetoelectricity, which is magnetically-induced electric polarization, observed in the hexaferrite is discussed in terms of the temperature-dependent magnetic structure at zero field.

Near room temperature operation of a highly strained short wavelength (2.1 µm) AlAs/In0.84Ga0.16As/AlAs/InAlAs QWIP

NASA Astrophysics Data System (ADS)

Mohamed, A. H.; Missous, M.; Lai, K. T.; Haywood, S. K.

2006-06-01

A strain-compensated AlAs/InxGa1-xAs/AlAs/InyAl1-yAs (x ap 0.8, y ap 0.5) quantum well infrared photodetector (QWIP) structure was grown by molecular beam epitaxy (MBE). Conditions of exact stoichiometric growth were applied at a temperature of ~420 °C to produce structures capable of detecting IR radiation in the 2-5 µm mid-infrared spectrum. Double crystal x-ray diffraction (DCXRD) and room temperature photoluminescence (PL) experiments confirmed the excellent structural characteristics of the grown material system. A strong room temperature intersubband absorption peak was observed at a wavelength of 2.16 µm. Current-voltage (I-V) measurements as a function of temperature were carried out to electrically characterize the fabricated QWIP devices yielding devices working under background limited infrared photodetection (BLIP) conditions at 270 K. From the I-V curves, an activation energy of 270 meV at zero bias was extracted. This is in good agreement with a current transport mechanism which is dominated by thermionic emission. Photocurrent measurements were carried out and we demonstrate devices that are capable of working at a temperature as high as 270 K at a wavelength of 2.1 µm. The experimental results are in excellent agreement with the modelled values.

Observations on the relationship of structure to the mechanical properties of thin TD-NiCr sheet

NASA Technical Reports Server (NTRS)

Whittenberger, J. D.

1976-01-01

A study of the relationship between structure and mechanical properties of thin TD-NiCr sheet indicated that the elevated temperature tensile, stress-rupture, and creep strength properties are dependent on grain aspect ratio and sheet thickness. In general, the strength properties increase with increasing grain aspect ratio and sheet thickness. Tensile testing revealed an absence of ductility at elevated temperatures (not less than 1144 K). Significant creep damage as determined by subsequent tensile testing at room temperature occurs after very small amounts (less than 0.1%) of prior creep deformation over the temperature range 1144-1477 K. A threshold stress for creep appears to exist. Creep exposure below the threshold stress at T not less than 1366 K results in almost full retention of room temperature tensile properties.

Thermal and structural alternations in CuAlMnNi shape memory alloy by the effect of different pressure applications

NASA Astrophysics Data System (ADS)

Canbay, Canan Aksu; Polat, Tercan

2017-09-01

In this work the effects of the applied pressure on the characteristic transformation temperatures, the high temperature order-disorder phase transitions, the variation in diffraction peaks and the surface morphology of the CuAlMnNi shape memory alloy was investigated. The evolution of the transformation temperatures was studied by differential scanning calorimetry (DSC) with different heating and cooling rates. The differential thermal analysis measurements were performed to obtain the ordered-disordered phase transformations from room temperature to 900 °C. The characteristic transformation temperatures and the thermodynamic parameters were highly sensitive to variations in the applied pressure and also the applied pressure affected the thermodynamic parameters. The activation energy of the sample according to applied pressure values calculated by Kissinger method. The structural changes of the samples were studied by X-ray diffraction (XRD) measurements and by optical microscope observations at room temperature.

Substrate effects on photoluminescence and low temperature phase transition of methylammonium lead iodide hybrid perovskite thin films

NASA Astrophysics Data System (ADS)

Shojaee, S. A.; Harriman, T. A.; Han, G. S.; Lee, J.-K.; Lucca, D. A.

2017-07-01

We examine the effects of substrates on the low temperature photoluminescence (PL) spectra and phase transition in methylammonium lead iodide hybrid perovskite (CH3NH3PbI3) thin films. Structural characterization at room temperature with X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy indicated that while the chemical structure of films deposited on glass and quartz was similar, the glass substrate induced strain in the perovskite films and suppressed the grain growth. The luminescence response and phase transition of the perovskite thin films were studied by PL spectroscopy. The induced strain was found to affect both the room temperature and low temperature PL spectra of the hybrid perovskite films. In addition, it was found that the effects of the glass substrate inhibited a tetragonal to orthorhombic phase transition such that it occurred at lower temperatures.

Room-temperature ductile inorganic semiconductor.

PubMed

Shi, Xun; Chen, Hongyi; Hao, Feng; Liu, Ruiheng; Wang, Tuo; Qiu, Pengfei; Burkhardt, Ulrich; Grin, Yuri; Chen, Lidong

2018-05-01

Ductility is common in metals and metal-based alloys, but is rarely observed in inorganic semiconductors and ceramic insulators. In particular, room-temperature ductile inorganic semiconductors were not known until now. Here, we report an inorganic α-Ag 2 S semiconductor that exhibits extraordinary metal-like ductility with high plastic deformation strains at room temperature. Analysis of the chemical bonding reveals systems of planes with relatively weak atomic interactions in the crystal structure. In combination with irregularly distributed silver-silver and sulfur-silver bonds due to the silver diffusion, they suppress the cleavage of the material, and thus result in unprecedented ductility. This work opens up the possibility of searching for ductile inorganic semiconductors/ceramics for flexible electronic devices.

Microporous crystals and synthesis schemes

DOEpatents

Tumas, William; Ott, Kevin C.; McCleskey, T. Mark; Yates, Matthew Z.; Birnbaum, Eva R.

2008-04-22

Novel zeolites are produced by combining a polar solute, a silicon or phosphorous source, and a structure directing agent. Surfactants and a hydrophobic solvent are added to the previously mixed three species and shaken to disperse the surfactants. The reverse microemulsion is stirred overnight, at about room temperature and then iced for five to ten minutes. A metal source is added vigorously shaken for about two minutes. The mixture is then aged for about two hours at about room temperature. A mineralizer is added and the resultant mixture aged for about two hours at about room temperature. The mixture is heated to about 180.degree. C., for a suitable time period. The final novel product is then isolated.

Microporous crystals and synthesis schemes

DOEpatents

Tumas, William; Ott, Kevin C.; McCleskey, T. Mark; Yates, Matthew Z.; Birnbaum, Eva R.

2005-09-27

Novel zeolites are produced by combining a polar solute, a silicon or phosphorous source, and a structure directing agent. Surfactants and a hydrophobic solvent are added to the previously mixed three species and shaken to disperse the surfactants. The reverse microemulsion is stirred overnight, at about room temperature and then iced for five to ten minutes. A metal source is added vigorously shaken for about two minutes. The mixture is then aged for about two hours at about room temperature. A mineralizer is added and the resultant mixture aged for about two hours at about room temperature. The mixture is heated to about 180.degree. C., for a suitable time period. The final novel product is then isolated.

Room-temperature ductile inorganic semiconductor

NASA Astrophysics Data System (ADS)

Shi, Xun; Chen, Hongyi; Hao, Feng; Liu, Ruiheng; Wang, Tuo; Qiu, Pengfei; Burkhardt, Ulrich; Grin, Yuri; Chen, Lidong

2018-05-01

Ductility is common in metals and metal-based alloys, but is rarely observed in inorganic semiconductors and ceramic insulators. In particular, room-temperature ductile inorganic semiconductors were not known until now. Here, we report an inorganic α-Ag2S semiconductor that exhibits extraordinary metal-like ductility with high plastic deformation strains at room temperature. Analysis of the chemical bonding reveals systems of planes with relatively weak atomic interactions in the crystal structure. In combination with irregularly distributed silver-silver and sulfur-silver bonds due to the silver diffusion, they suppress the cleavage of the material, and thus result in unprecedented ductility. This work opens up the possibility of searching for ductile inorganic semiconductors/ceramics for flexible electronic devices.

Laterally biased structures for room temperature operation of quantum-well infrared photodetectors

NASA Astrophysics Data System (ADS)

Guzmán, Álvaro; Gargallo-Caballero, Raquel; Lü, Xiang; Grahn, Holger T.

2017-11-01

Laterally biased quantum-well infrared photodetectors (LBQWIPs) are expected to exhibit a photoresponse at room temperature. In these devices, the photocurrent is collected by means of two lateral Ohmic contacts on each side of an undoped quantum well (QW), which is coupled by tunneling to another n-doped QW. Photoexcited electrons from the n-doped QW tunnel through to the undoped QW and are swept out via a lateral bias voltage. Up to now, the practical development of these structures has not been yet achieved due to the difficulty of contacting single QWs separated by a few nanometers. In this paper, we report on a viable technology to fabricate LBQWIPs. We present two procedures to contact individual QWs, which are sufficiently close to be coupled by tunneling. The final devices exhibit very low dark-current values and clear infrared absorption peaks at 300 K, in good agreement with the results of numerical simulations. This work demonstrates the practical functionality of the laterally biased structure and paves the way for future developments of room temperature QWIPs.

Recrystallization in Si upon ion irradiation at room temperature in Co/Si(111) thin film systems

NASA Astrophysics Data System (ADS)

Banu, Nasrin; Satpati, B.; Dev, B. N.

2018-04-01

After several decades of research it was concluded that for a constant flux recrystallization in Si upon ion irradiation is possible only at high temperature. At low temperature or at room temperature only amorphization can take place. However we have observed recrystallization in Si upon ion irradiation at room temperature in a Co/Si thin film system. The Co/Si sample was prepared by deposition of 25 nm Co on clean Si(111) substrate. An oxide layer (˜ 2nm) of cobalt at the top of the film due to air exposure. The ion irradiation was done at room temperature under high vacuum with 1MeV Si+ ion with low beam current < 400 nA. Earlier we have shown similar ion induced recrystallization in Si(100) substrate which had a sandwich Si/Ni/Si structure. This system had an epitaxial buffer Si layer on Si substrate. This study also shows that the phenomenon is independent of substrate orientation and buffer layer. We have used transmission electron microscopy (TEM) to study the recrystallization behavior.

Ion transport and structural dynamics in homologous ammonium and phosphonium-based room temperature ionic liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griffin, Philip J., E-mail: pgrif@seas.upenn.edu; Holt, Adam P.; Tsunashima, Katsuhiko

2015-02-28

Charge transport and structural dynamics in a homologous pair of ammonium and phosphonium based room temperature ionic liquids (ILs) have been characterized over a wide temperature range using broadband dielectric spectroscopy and quasi-elastic light scattering spectroscopy. We have found that the ionic conductivity of the phosphonium based IL is significantly enhanced relative to the ammonium homolog, and this increase is primarily a result of a lower glass transition temperature and higher ion mobility. Additionally, these ILs exhibit pronounced secondary relaxations which are strongly influenced by the atomic identity of the cation charge center. While the secondary relaxation in the phosphoniummore » IL has the expected Arrhenius temperature dependence characteristic of local beta relaxations, the corresponding relaxation process in the ammonium IL was found to exhibit a mildly non-Arrhenius temperature dependence in the measured temperature range—indicative of molecular cooperativity. These differences in both local and long-range molecular dynamics are a direct reflection of the subtly different inter-ionic interactions and mesoscale structures found in these homologous ILs.« less

Ion transport and structural dynamics in homologous ammonium and phosphonium-based room temperature ionic liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griffin, Phillip J.; Holt, Adam P.; Tsunashima, Katsuhiko

2015-02-01

Charge transport and structural dynamics in a homologous pair of ammonium and phosphonium based room temperature ionic liquids (ILs) have been characterized over a wide temperature range using broadband dielectric spectroscopy and quasi-elastic light scattering spectroscopy. We have found that the ionic conductivity of the phosphonium based IL is significantly enhanced relative to the ammonium homolog, and this increase is primarily a result of a lower glass transition temperature and higher ion mobility. Additionally, these ILs exhibit pronounced secondary relaxations which are strongly influenced by the atomic identity of the cation charge center. While the secondary relaxation in the phosphoniummore » IL has the expected Arrhenius temperature dependence characteristic of local beta relaxations, the corresponding relaxation process in the ammonium IL was found to exhibit a mildly non-Arrhenius temperature dependence in the measured temperature range-indicative of molecular cooperativity. These differences in both local and long-range molecular dynamics are a direct reflection of the subtly different inter-ionic interactions and mesoscale structures found in these homologous ILs.« less

The room temperature crystal structure of a bacterial phytochrome determined by serial femtosecond crystallography

DOE PAGES

Edlund, Petra; Takala, Heikki; Claesson, Elin; ...

2016-10-19

Phytochromes are a family of photoreceptors that control light responses of plants, fungi and bacteria. A sequence of structural changes, which is not yet fully understood, leads to activation of an output domain. Time-resolved serial femtosecond crystallography (SFX) can potentially shine light on these conformational changes. Here we report the room temperature crystal structure of the chromophore-binding domains of the Deinococcus radiodurans phytochrome at 2.1 Å resolution. The structure was obtained by serial femtosecond X-ray crystallography from microcrystals at an X-ray free electron laser. We find overall good agreement compared to a crystal structure at 1.35 Å resolution derived frommore » conventional crystallography at cryogenic temperatures, which we also report here. The thioether linkage between chromophore and protein is subject to positional ambiguity at the synchrotron, but is fully resolved with SFX. As a result, the study paves the way for time-resolved structural investigations of the phytochrome photocycle with time-resolved SFX.« less

The room temperature crystal structure of a bacterial phytochrome determined by serial femtosecond crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Edlund, Petra; Takala, Heikki; Claesson, Elin

Phytochromes are a family of photoreceptors that control light responses of plants, fungi and bacteria. A sequence of structural changes, which is not yet fully understood, leads to activation of an output domain. Time-resolved serial femtosecond crystallography (SFX) can potentially shine light on these conformational changes. Here we report the room temperature crystal structure of the chromophore-binding domains of the Deinococcus radiodurans phytochrome at 2.1 Å resolution. The structure was obtained by serial femtosecond X-ray crystallography from microcrystals at an X-ray free electron laser. We find overall good agreement compared to a crystal structure at 1.35 Å resolution derived frommore » conventional crystallography at cryogenic temperatures, which we also report here. The thioether linkage between chromophore and protein is subject to positional ambiguity at the synchrotron, but is fully resolved with SFX. As a result, the study paves the way for time-resolved structural investigations of the phytochrome photocycle with time-resolved SFX.« less

Understanding the impact of nanoscale aggregation on charge transport and structural dynamics in room temperature ionic liquids

NASA Astrophysics Data System (ADS)

Griffin, Philip; Holt, Adam; Wang, Yangyang; Sokolov, Alexei

2015-03-01

Amphiphilic room temperature ionic liquids (ILs) segregate on the nanoscale, forming intricate networks of charge-rich ionic domains intercalated with charge-poor aliphatic domains. While this structural phenomenon has been well established through x-ray diffraction studies and atomistic MD simulations, the precise effects of nanophase segregation on ion transport and structural dynamics in ILs remains poorly understood. Using a combination of broadband dielectric spectroscopy, light scattering spectroscopy, and rheology, we have characterized the ionic conductivity, structural dynamics, and shear viscosity of a homologous series of quaternary ammonium ionic liquids over a wide temperature range. Upon increasing the length and volume fraction of the alkyl side chains of these quaternary ammonium ILs, ionic conductivity decreases precipitously, although no corresponding slowing of the structural dynamics is observed. Instead, we identify the dynamical signature of supramolecular aggregates. Our results directly demonstrate the role that chemical structure and ionic aggregation plays in determining the charge transport properties of amphiphilic ILs.

Room-temperature solution synthesis of Ag nanoparticle functionalized molybdenum oxide nanowires and their catalytic applications.

PubMed

Dong, Wenjun; Huang, Huandi; Zhu, Yanjun; Li, Xiaoyun; Wang, Xuebin; Li, Chaorong; Chen, Benyong; Wang, Ge; Shi, Zhan

2012-10-26

A simple chemical solution route for the synthesis of large-scale high-quality Ag nanoparticle functionalized molybdenum oxide nanowire at room temperature has been developed. In the synthesis, the protonated amine was intercalated into the molybdenum bronze layers to reduce the electrostatic force of the lamellar structures, and then the Ag nanoparticle functionalized long nanowires could be easily induced by a redox reaction between a molybdenum oxide-amine intermediate and Ag(+) at room temperature. The intercalation lamellar structures improved the nucleation and growth of the Ag nanoparticles, with the result that uniform Ag nanoparticles occurred on the surface of the MoO(3) nanowire. In this way Ag nanoparticles with average sizes of around 6 nm, and high-purity nanowires with mean diameter of around 50 nm and with typical lengths of several tens to hundreds of micrometers were produced. The heteronanostructured nanowires were intricately and inseparably connected to each other with hydrogen bonds and/or bridge oxygen atoms and packed together, forming a paper-like porous network film. The Ag-MoO(3) nanowire film performs a promoted catalytic property for the epoxidation of cis-cyclooctene, and the heteronanostructured nanowire film sensor shows excellent sensing performance to hydrogen and oxygen at room temperature.

The effect of high-pressure torsion on the microstructure and properties of magnesium

NASA Astrophysics Data System (ADS)

Figueiredo, Roberto B.; Sabbaghianrad, Shima; Langdon, Terence G.

2017-05-01

High-pressure torsion provides the opportunity to introduce significant plastic strain at room temperature in magnesium and its alloys. It is now established that this processing operation produces ultrafine-grained structures and changes the properties of these materials. The present paper shows that the mechanism of grain refinement differs from f.c.c. and b.c.c. materials. It is shown that fine grains are formed at the grain boundaries of coarse grains and gradually consume the whole structure. Also, the processed material exhibits unusual mechanical properties due to the activation of grain boundary sliding at room temperature.

Submilliampere continuous-wave room-temperature lasing operation of a GaAs mushroom structure surface-emitting laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Y.J.; Dziura, T.G.; Wang, S.C.

1990-05-07

We report a GaAs mushroom structure surface-emitting laser at 900 nm with submilliampere (0.2--0.5 mA) threshold under room-temperature cw operation for the first time. The very low threshold current was achieved on devices which consisted of a 2--4 {mu}m diameter active region formed by chemical selective etching, and sandwiched between two Al{sub 0.05}Ga{sub 0.95} As/ Al{sub 0.53}Ga{sub 0.47} As distributed Bragg reflectors of very high reflectivity (98--99%) grown by metalorganic chemical vapor deposition.

Submilliampere continuous-wave room-temperature lasing operation of a GaAs mushroom structure surface-emitting laser

NASA Astrophysics Data System (ADS)

Yang, Ying Jay; Dziura, Thaddeus G.; Wang, S. C.; Hsin, Wei; Wang, Shyh

1990-05-01

We report a GaAs mushroom structure surface-emitting laser at 900 nm with submilliampere (0.2-0.5 mA) threshold under room-temperature cw operation for the first time. The very low threshold current was achieved on devices which consisted of a 2-4 μm diameter active region formed by chemical selective etching, and sandwiched between two Al0.05Ga0.95 As/ Al0.53Ga0.47 As distributed Bragg reflectors of very high reflectivity (98-99%) grown by metalorganic chemical vapor deposition.

Double-flow focused liquid injector for efficient serial femtosecond crystallography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oberthuer, Dominik; Knoška, Juraj; Wiedorn, Max O.

Serial femtosecond crystallography requires reliable and efficient delivery of fresh crystals across the beam of an X-ray free-electron laser over the course of an experiment. We introduce a double-flow focusing nozzle to meet this challenge, with significantly reduced sample consumption, while improving jet stability over previous generations of nozzles. We demonstrate its use to determine the first room-temperature structure of RNA polymerase II at high resolution, revealing new structural details. Furthermore, the double flow-focusing nozzles were successfully tested with three other protein samples and the first room temperature structure of an extradiol ring-cleaving dioxygenase was solved by utilizing the improvedmore » operation and characteristics of these devices.« less

Double-flow focused liquid injector for efficient serial femtosecond crystallography

PubMed Central

Oberthuer, Dominik; Knoška, Juraj; Wiedorn, Max O.; Beyerlein, Kenneth R.; Bushnell, David A.; Kovaleva, Elena G.; Heymann, Michael; Gumprecht, Lars; Kirian, Richard A.; Barty, Anton; Mariani, Valerio; Tolstikova, Aleksandra; Adriano, Luigi; Awel, Salah; Barthelmess, Miriam; Dörner, Katerina; Xavier, P. Lourdu; Yefanov, Oleksandr; James, Daniel R.; Nelson, Garrett; Wang, Dingjie; Calvey, George; Chen, Yujie; Schmidt, Andrea; Szczepek, Michael; Frielingsdorf, Stefan; Lenz, Oliver; Snell, Edward; Robinson, Philip J.; Šarler, Božidar; Belšak, Grega; Maček, Marjan; Wilde, Fabian; Aquila, Andrew; Boutet, Sébastien; Liang, Mengning; Hunter, Mark S.; Scheerer, Patrick; Lipscomb, John D.; Weierstall, Uwe; Kornberg, Roger D.; Spence, John C. H.; Pollack, Lois; Chapman, Henry N.; Bajt, Saša

2017-01-01

Serial femtosecond crystallography requires reliable and efficient delivery of fresh crystals across the beam of an X-ray free-electron laser over the course of an experiment. We introduce a double-flow focusing nozzle to meet this challenge, with significantly reduced sample consumption, while improving jet stability over previous generations of nozzles. We demonstrate its use to determine the first room-temperature structure of RNA polymerase II at high resolution, revealing new structural details. Moreover, the double flow-focusing nozzles were successfully tested with three other protein samples and the first room temperature structure of an extradiol ring-cleaving dioxygenase was solved by utilizing the improved operation and characteristics of these devices. PMID:28300169

Double-flow focused liquid injector for efficient serial femtosecond crystallography

DOE PAGES

Oberthuer, Dominik; Knoška, Juraj; Wiedorn, Max O.; ...

2017-03-16

Serial femtosecond crystallography requires reliable and efficient delivery of fresh crystals across the beam of an X-ray free-electron laser over the course of an experiment. We introduce a double-flow focusing nozzle to meet this challenge, with significantly reduced sample consumption, while improving jet stability over previous generations of nozzles. We demonstrate its use to determine the first room-temperature structure of RNA polymerase II at high resolution, revealing new structural details. Furthermore, the double flow-focusing nozzles were successfully tested with three other protein samples and the first room temperature structure of an extradiol ring-cleaving dioxygenase was solved by utilizing the improvedmore » operation and characteristics of these devices.« less

High Electron Mobility Transistor Structures on Sapphire Substrates Using CMOS Compatible Processing Techniques

NASA Technical Reports Server (NTRS)

Mueller, Carl; Alterovitz, Samuel; Croke, Edward; Ponchak, George

2004-01-01

System-on-a-chip (SOC) processes are under intense development for high-speed, high frequency transceiver circuitry. As frequencies, data rates, and circuit complexity increases, the need for substrates that enable high-speed analog operation, low-power digital circuitry, and excellent isolation between devices becomes increasingly critical. SiGe/Si modulation doped field effect transistors (MODFETs) with high carrier mobilities are currently under development to meet the active RF device needs. However, as the substrate normally used is Si, the low-to-modest substrate resistivity causes large losses in the passive elements required for a complete high frequency circuit. These losses are projected to become increasingly troublesome as device frequencies progress to the Ku-band (12 - 18 GHz) and beyond. Sapphire is an excellent substrate for high frequency SOC designs because it supports excellent both active and passive RF device performance, as well as low-power digital operations. We are developing high electron mobility SiGe/Si transistor structures on r-plane sapphire, using either in-situ grown n-MODFET structures or ion-implanted high electron mobility transistor (HEMT) structures. Advantages of the MODFET structures include high electron mobilities at all temperatures (relative to ion-implanted HEMT structures), with mobility continuously improving to cryogenic temperatures. We have measured electron mobilities over 1,200 and 13,000 sq cm/V-sec at room temperature and 0.25 K, respectively in MODFET structures. The electron carrier densities were 1.6 and 1.33 x 10(exp 12)/sq cm at room and liquid helium temperature, respectively, denoting excellent carrier confinement. Using this technique, we have observed electron mobilities as high as 900 sq cm/V-sec at room temperature at a carrier density of 1.3 x 10(exp 12)/sq cm. The temperature dependence of mobility for both the MODFET and HEMT structures provides insights into the mechanisms that allow for enhanced electron mobility as well as the processes that limit mobility, and will be presented.

Electromigration and morphological changes in Ag nanostructures

NASA Astrophysics Data System (ADS)

Chatterjee, A.; Bai, T.; Edler, F.; Tegenkamp, C.; Weide-Zaage, K.; Pfnür, H.

2018-02-01

Electromigration (EM) as a structuring tool was investigated in Ag nanowires (width 300 nm, thickness 25 nm) and partly in notched and bow-tie Ag structures on a Si(1 0 0) substrate in ultra-high vacuum using a four-tip scanning tunneling microscope in combination with a scanning electron microscope. From simulations of Ag nanowires we got estimates of temperature profiles, current density profiles, EM and thermal migration (TM) mass flux distributions within the nanowire induced by critical current densities of 108 A cm-2. At room temperature, the electron wind force at these current densities by far dominates over thermal diffusion, and is responsible for formation of voids at the cathode and hillocks at the anode side. For current densities that exceed the critical current densities necessary for EM, a new type of wire-like structure formation was found both at room temperature and at 100 K for notched and bow-tie structures. This suggests that the simultaneous action of EM and TM is structure forming, but with a very small influence of TM at low temperature.

Magnetism and structure of a half-metallic Heusler compound Co-Mn-Cr-Si

NASA Astrophysics Data System (ADS)

Huh, Yung; Joshi, Swarangi; Jain, Sanmati; Pathak, Ojas; Kharel, Parashu

Half metallic ferromagnetic Heusler compounds have a potential in the development of spintronic devices for its high spin polarization at the Fermi level and lattice structure compatibility. Heusler compounds based on cobalt are considered a good candidate for room temperature half-metals due to their high Curie temperature. Co2CrSi is one of such predicted half-metal, but it is meta-stable and difficult to synthesize in the desired crystal structure. We have successfully synthesized a Heusler compound Co2Mn0.5Cr0.5Si by using arc melting and rapid quenching followed by thermal treatment under high vacuum to control any parasitic contamination. Crystal X-ray diffraction pattern shows the samples crystallize in a cubic Heusler structure with some degrees of structural disorder. Curie temperatures of the prepared samples are observed well beyond room temperature near 900 K. Magnetic anomalies present in as-prepared samples are cleared, and its magnetic properties are improved by thermal treatment. This research is supported by Academic and Scholarly Excellence Funds, and Research/Scholarship Support Fund, South Dakota State University.

A multi-state synthetic ferrimagnet with controllable switching near room temperature

NASA Astrophysics Data System (ADS)

Franco, A. F.; Landeros, P.

2018-06-01

Ferrite composites with temperature-induced magnetization reversal, and synthetic ferrimagnets and antiferromagnets have been of great interest to the scientific community due to their uncommon thermal properties and potential applications in magnetic storage, spintronic devices, and several other fields. One of the advantages of these structures is the strong antiferromagnetic coupling, which stabilizes the magnetization state and gives access to interesting static and dynamical magnetic behaviors. Some of their drawbacks lie in that it is difficult to induce temperature-induced magnetization reversal at room temperature in composites, and that the strong interaction makes it difficult to induce a parallel magnetization state (and thus a high magnetic moment). In this work, we study numerically the magnetization behaviour of a Cu(1 0 0)/Ni/Pt/[Co/Pt]4 synthetic ferrimagnet and show that is possible to revert the sign of its magnetization by varying the temperature in ranges around room temperature. We also show that the four parallel and antiparallel magnetization states are stable at temperatures up to 360 K, and demonstrate that it is possible to change deterministically between these states by increasing the temperature of the device and/or applying a magnetic field, showcasing simultaneous non-hysteretic and hysteretic switching processes induced by temperature. Thus, this structure opens the possibility to have reconfigurable magnetic devices with multiple purposes based on the nature of the different switching events and the interplay between them.

Single-Mode Near-Infrared Lasing in a GaAsSb-Based Nanowire Superlattice at Room Temperature.

PubMed

Ren, Dingding; Ahtapodov, Lyubomir; Nilsen, Julie S; Yang, Jianfeng; Gustafsson, Anders; Huh, Junghwan; Conibeer, Gavin J; van Helvoort, Antonius T J; Fimland, Bjørn-Ove; Weman, Helge

2018-04-11

Semiconductor nanowire lasers can produce guided coherent light emission with miniaturized geometry, bringing about new possibilities for a variety of applications including nanophotonic circuits, optical sensing, and on-chip and chip-to-chip optical communications. Here, we report on the realization of single-mode and room-temperature lasing from 890 to 990 nm, utilizing a novel design of single nanowires with GaAsSb-based multiple axial superlattices as a gain medium under optical pumping. The control of lasing wavelength via compositional tuning with excellent room-temperature lasing performance is shown to result from the unique nanowire structure with efficient gain material, which delivers a low lasing threshold of ∼6 kW/cm 2 (75 μJ/cm 2 per pulse), a lasing quality factor as high as 1250, and a high characteristic temperature of ∼129 K. These results present a major advancement for the design and synthesis of nanowire laser structures, which can pave the way toward future nanoscale integrated optoelectronic systems with superior performance.

Extremely elevated room-temperature kinetic isotope effects quantify the critical role of barrier width in enzymatic C-H activation.

PubMed

Hu, Shenshen; Sharma, Sudhir C; Scouras, Alexander D; Soudackov, Alexander V; Carr, Cody A Marcus; Hammes-Schiffer, Sharon; Alber, Tom; Klinman, Judith P

2014-06-11

The enzyme soybean lipoxygenase (SLO) has served as a prototype for hydrogen-tunneling reactions, as a result of its unusual kinetic isotope effects (KIEs) and their temperature dependencies. Using a synergy of kinetic, structural, and theoretical studies, we show how the interplay between donor-acceptor distance and active-site flexibility leads to catalytic behavior previously predicted by quantum tunneling theory. Modification of the size of two hydrophobic residues by site-specific mutagenesis in SLO reduces the reaction rate 10(4)-fold and is accompanied by an enormous and unprecedented room-temperature KIE. Fitting of the kinetic data to a non-adiabatic model implicates an expansion of the active site that cannot be compensated by donor-acceptor distance sampling. A 1.7 Å resolution X-ray structure of the double mutant further indicates an unaltered backbone conformation, almost identical side-chain conformations, and a significantly enlarged active-site cavity. These findings show the compelling property of room-temperature hydrogen tunneling within a biological context and demonstrate the very high sensitivity of such tunneling to barrier width.

Ab initio structure determination of nanocrystals of organic pharmaceutical compounds by electron diffraction at room temperature using a Timepix quantum area direct electron detector.

PubMed

van Genderen, E; Clabbers, M T B; Das, P P; Stewart, A; Nederlof, I; Barentsen, K C; Portillo, Q; Pannu, N S; Nicolopoulos, S; Gruene, T; Abrahams, J P

2016-03-01

Until recently, structure determination by transmission electron microscopy of beam-sensitive three-dimensional nanocrystals required electron diffraction tomography data collection at liquid-nitrogen temperature, in order to reduce radiation damage. Here it is shown that the novel Timepix detector combines a high dynamic range with a very high signal-to-noise ratio and single-electron sensitivity, enabling ab initio phasing of beam-sensitive organic compounds. Low-dose electron diffraction data (∼ 0.013 e(-) Å(-2) s(-1)) were collected at room temperature with the rotation method. It was ascertained that the data were of sufficient quality for structure solution using direct methods using software developed for X-ray crystallography (XDS, SHELX) and for electron crystallography (ADT3D/PETS, SIR2014).

Room-temperature semiconductor heterostructure refrigeration

NASA Astrophysics Data System (ADS)

Chao, K. A.; Larsson, Magnus; Mal'shukov, A. G.

2005-07-01

With the proper design of semiconductor tunneling barrier structures, we can inject low-energy electrons via resonant tunneling, and take out high-energy electrons via a thermionic process. This is the operation principle of our semiconductor heterostructure refrigerator (SHR) without the need of applying a temperature gradient across the device. Even for the bad thermoelectric material AlGaAs, our calculation shows that at room temperature, the SHR can easily lower the temperature by 5-7K. Such devices can be fabricated with the present semiconductor technology. Besides its use as a kitchen refrigerator, the SHR can efficiently cool microelectronic devices.

Room temperature magnetism and metal to semiconducting transition in dilute Fe doped Sb1-xSex semiconducting alloy thin films

NASA Astrophysics Data System (ADS)

Agrawal, Naveen; Sarkar, Mitesh; Chawda, Mukesh; Ganesan, V.; Bodas, Dhananjay

2015-02-01

The magnetism was observed in very dilute Fe doped alloy thin film Fe0.008Sb1-xSex, for x = 0.01 to 0.10. These thin films were grown on silicon substrate using thermal evaporation technique. Structural, electrical, optical, charge carrier concentration measurement, surface morphology and magnetic properties were observed using glancing incidence x-ray diffraction (GIXRD), four probe resistivity, photoluminescence, Hall measurement, atomic force microscopy (AFM) and magnetic force microscopy (MFM) techniques, respectively. No peaks of iron were seen in GIXRD. The resistivity results show that activation energy increases with increase in selenium (Se) concentration. The Arrhenius plot reveals metallic behavior below room temperature. The low temperature conduction is explained by variable range-hopping mechanism, which fits very well in the temperature range 150-300 K. The decrease in density of states has been observed with increasing selenium concentration (x = 0.01 to 0.10). There is a metal-to-semiconductor phase transition observed above room temperature. This transition temperature is Se concentration dependent. The particle size distribution ˜47-61 nm is evaluated using AFM images. These thin films exhibit ferromagnetic interactions at room temperature.

A Temperature‐Responsive Smart Europium Metal‐Organic Framework Switch for Reversible Capture and Release of Intrinsic Eu3+ Ions

PubMed Central

Zhu, Min; Song, Xue‐Zhi; Zhao, Shu‐Na; Meng, Xing; Wu, Lan‐Lan; Wang, Cheng

2015-01-01

Stimuli‐responsive structural transformations are emerging as a scaffold to develop a charming class of smart materials. A EuL metal‐organic framework (MOF) undergoes a reversible temperature‐stimulated single‐crystal to single‐crystal transformation, showing a specific behavior of fast capture/release of free Eu3+ in the channels at low and room temperatures. At room temperature, compound 1a is obtained with one free carboxylate group severing as further hook, featuring one‐dimensional square channels filled with intrinsic free europium ions. Trigged by lowering the ambient temperature, 1b is gained. In 1b, the intrinsic free europium ions can be fast captured by the carboxylate‐hooks anchored in the framework, resulting in the structural change and its channel distortion. To the best of our knowledge, this is the first report of such a rapid and reversible switch stemming from dynamic control between noncovalent and covalent Eu–ligand interactions. Utilizing EuL MOF to detect highly explosive 2,4,6‐trinitrophenol at room temperature and low temperature provides a glimpse into the potential of this material in fluorescence sensors. PMID:27980931

Evolution of Ge nanoislands on Si(110)-'16 × 2' surface under thermal annealing studied using STM

NASA Astrophysics Data System (ADS)

Gangopadhyay, Subhashis; Yoshimura, Masamichi; Ueda, Kazuyuki

2009-11-01

The initial nucleation of Ge nanoclusters on Si(110) at room temperature (RT), annealing-induced surface roughening and the evolution of three-dimensional Ge nanoislands have been investigated using scanning tunneling microscopy (STM). A few monolayers (ML) of Ge deposited at room temperature lead to the formation of Ge clusters which are homogeneously distributed across the surface. The stripe-like patterns, characteristic of the Si(110)-'16 × 2' surface reconstruction are also retained. Increasing annealing temperatures, however, lead to significant surface diffusion and thus, disruption of the underlying '16 × 2' reconstruction. The annealing-induced removal of the stripe structures (originated from '16 × 2' reconstruction) starts at approximately 300 °C, whereas the terrace structures of Si(110) are thermally stable up to 500 °C. At approximately 650 °C, shallow Ge islands of pyramidal shape with (15,17,1) side facets start to form. Annealing at even higher temperatures enhances Ge island formation. Our findings are explained in terms of partial dewetting of the metastable Ge wetting layer (WL) (formed at room temperature) as well as partial relaxation of lattice strain through three-dimensional (3D) island growth.

Polymer functionalized nanostructured porous silicon for selective water vapor sensing at room temperature

NASA Astrophysics Data System (ADS)

Dwivedi, Priyanka; Das, Samaresh; Dhanekar, Saakshi

2017-04-01

This paper highlights the surface treatment of porous silicon (PSi) for enhancing the sensitivity of water vapors at room temperature. A simple and low cost technique was used for fabrication and functionalization of PSi. Spin coated polyvinyl alcohol (PVA) was used for functionalizing PSi surface. Morphological and structural studies were conducted to analyze samples using SEM and XRD/Raman spectroscopy respectively. Contact angle measurements were performed for assessing the wettability of the surfaces. PSi and functionalized PSi samples were tested as sensors in presence of different analytes like ethanol, acetone, isopropyl alcohol (IPA) and water vapors in the range of 50-500 ppm. Electrical measurements were taken from parallel aluminium electrodes fabricated on the functionalized surface, using metal mask and thermal evaporation. Functionalized PSi sensors in comparison to non-functionalized sensors depicted selective and enhanced response to water vapor at room temperature. The results portray an efficient and selective water vapor detection at room temperature.

Tunable room-temperature single-photon emission at telecom wavelengths from sp 3 defects in carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Xiaowei; Hartmann, Nicolai F.; Ma, Xuedan

Generating quantum light emitters that operate at room temperature and at telecom wavelengths remains a significant materials challenge. To achieve this goal requires light sources that emit in the near-infrared wavelength region and that, ideally, are tunable to allow desired output wavelengths to be accessed in a controllable manner. Here, we show that exciton localization at covalently introduced aryl sp 3 defect sites in single-walled carbon nanotubes provides a route to room-temperature single-photon emission with ultrahigh single-photon purity (99%) and enhanced emission stability approaching the shot-noise limit. Moreover, we demonstrate that the inherent optical tunability of single-walled carbon nanotubes, presentmore » in their structural diversity, allows us to generate room-temperature single-photon emission spanning the entire telecom band. Furthermore, single-photon emission deep into the centre of the telecom C band (1.55 um) is achieved at the largest nanotube diameters we explore (0.936 nm).« less

Room-temperature H2S Gas Sensor Based on Au-doped ZnFe2O4 Yolk-shell Microspheres.

PubMed

Yan, Yin; Nizamidin, Patima; Turdi, Gulmira; Kari, Nuerguli; Yimit, Abliz

2017-01-01

Room-temperature type H 2 S sensing devices that use Au-doped ZnFe 2 O 4 yolk-shell microspheres as the active material have been fabricated using a solvothermal method as well as subsequent annealing and a chemical etching process. The samples are characterized using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), field-emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). The results demonstrate that the doping of Au does not change the spinel structure of the products, which were yolk-shell microspheres, while the particle size varied with the Au doping concentration. Also, the as-fabricated sensor device exhibited excellent selectivity toward H 2 S gas at the room temperature; the gas-sensing property of 2 wt% Au-doped ZnFe 2 O 4 microspheres was the best. The Au-doped ZnFe 2 O 4 yolk-shell microspheres can be promising as a sensing material for H 2 S gas detecting at room temperature.

Room temperature ferroelectricity in one-dimensional single chain molecular magnets [{M(Δ)M(Λ)}(ox)2(phen)2]n (M = Fe and Mn)

NASA Astrophysics Data System (ADS)

Bhatt, Pramod; Mukadam, M. D.; Meena, S. S.; Mishra, S. K.; Mittal, R.; Sastry, P. U.; Mandal, B. P.; Yusuf, S. M.

2017-03-01

The ferroelectric materials are mainly focused on pure inorganic oxides; however, the organic molecule based materials have recently attracted great attention because of their multifunctional properties. The mixing of oxalate and phenanthroline ligands with metal ions (Fe or Mn) at room temperature followed by hydrothermal treatment results in the formation of one-dimensional single chain molecular magnets which exhibit room temperature dielectric and ferroelectric behavior. The compounds are chiral in nature, and exhibit a ferroelectric behavior, attributed to the polar point group C2, in which they crystallized. The compounds are also associated with a dielectric loss and thus a relaxation process. The observed electric dipole moment, essential for a ferroelectricity, has been understood quantitatively in terms of lattice distortions at two different lattice sites within the crystal structure. The studied single chain molecular magnetic materials with room temperature ferroelectric and dielectric properties could be of great technological importance in non-volatile memory elements, and high-performance insulators.

Biomimetic and Aggregation-Driven Crystallization Route for Room-Temperature Material Synthesis: Growth of β-Ga2O3 Nanoparticles Using Peptide Assemblies as Nanoreactors

PubMed Central

Lee, Sang-Yup; Gao, Xueyun; Matsui, Hiroshi

2008-01-01

The room temperature synthesis of β-Ga2O3 nanocrystal was examined by coupling two biomimetic crystallization techniques, the enzymatic peptide nano-assembly templating and the aggregation-driven crystallization. The catalytic template of peptide assembly nucleated and mineralized primary β-Ga2O3 crystals, and then fused them to grow single-crystalline and monodisperse nanoparticles in the cavity of the peptide assembly at room temperature. In this work, the peptide assembly was exploited as a nano-reactor with an enzymatic functionality catalyzing the hydrolysis of gallium precursors. In addition, the characteristic ring-structure of peptide assembly is expected to provide an efficient dehydration pathway and the crystallization control over the surface tension, which are advantageous for the β-Ga2O3 crystal growth. This multifunctional peptide assembly could be applied for syntheses of a variety of nanomaterials that are kinetically difficult to grow at room temperature. PMID:17302413

Tunable room-temperature single-photon emission at telecom wavelengths from sp 3 defects in carbon nanotubes

DOE PAGES

He, Xiaowei; Hartmann, Nicolai F.; Ma, Xuedan; ...

2017-07-31

Generating quantum light emitters that operate at room temperature and at telecom wavelengths remains a significant materials challenge. To achieve this goal requires light sources that emit in the near-infrared wavelength region and that, ideally, are tunable to allow desired output wavelengths to be accessed in a controllable manner. Here, we show that exciton localization at covalently introduced aryl sp 3 defect sites in single-walled carbon nanotubes provides a route to room-temperature single-photon emission with ultrahigh single-photon purity (99%) and enhanced emission stability approaching the shot-noise limit. Moreover, we demonstrate that the inherent optical tunability of single-walled carbon nanotubes, presentmore » in their structural diversity, allows us to generate room-temperature single-photon emission spanning the entire telecom band. Furthermore, single-photon emission deep into the centre of the telecom C band (1.55 um) is achieved at the largest nanotube diameters we explore (0.936 nm).« less

Structural damping studies at cryogenic temperatures

NASA Technical Reports Server (NTRS)

Young, Clarence P., Jr.; Buehrle, Ralph D.

1994-01-01

Results of an engineering study to measure changes in structural damping properties of two cryogenic wind tunnel model systems and two metallic test specimens at cryogenic temperatures are presented. Data are presented which indicate overall, a trend toward reduced structural damping at cryogenic temperatures (-250 degrees F) when compared with room temperature damping properties. The study was focused on structures and materials used for model systems tested in the National Transonic Facility (NTF). The study suggests that the significant reductions in damping at extremely cold temperatures are most likely associated with changes in mechanical joint compliance damping rather than changes in material (solid) damping.

Room Temperature Co-Precipitation Synthesis of Magnetite Nanoparticles in a Large pH Window with Different Bases.

PubMed

Mascolo, Maria Cristina; Pei, Yongbing; Ring, Terry A

2013-11-28

Magnetite nanoparticles (Fe₃O₄) represent the most promising materials in medical applications. To favor high-drug or enzyme loading on the nanoparticles, they are incorporated into mesoporous materials to form a hybrid support with the consequent reduction of magnetization saturation. The direct synthesis of mesoporous structures appears to be of interest. To this end, magnetite nanoparticles have been synthesized using a one pot co-precipitation reaction at room temperature in the presence of different bases, such as NaOH, KOH or (C₂H₅)₄NOH. Magnetite shows characteristics of superparamagnetism at room temperature and a saturation magnetization (Ms) value depending on both the crystal size and the degree of agglomeration of individual nanoparticles. Such agglomeration appears to be responsible for the formation of mesoporous structures, which are affected by the pH, the nature of alkali, the slow or fast addition of alkaline solution and the drying modality of synthesized powders.

Rietveld refinement, dielectric and magnetic properties of Nb modified Bi0.80Ba0.20FeO3 ceramic

NASA Astrophysics Data System (ADS)

Jangra, Sandhaya; Sanghi, Sujata; Agarwal, Ashish; Rangi, Manisha

2018-05-01

Bi0.80Ba0.20Fe0.95Nb0.05O3 ceramic has been prepared via conventional solid state reaction method. Structure analysis was carried out by X-ray diffraction (XRD) technique at room temperature. XRD pattern confirmed the crystalline nature of prepared sample. Rietveld analysis used for further structural investigations and confirmed the existence of rhombohedral symmetry (R3c space group). The dielectric response shows dispersion at lower frequency range and becomes frequency independent at high frequency. The approximation of conduction mechanism is determined by the temperature dependent behavior of frequency exponent `s'. Fitting results suggests the applicability of small polaron conduction mechanism at lower temperatures and CBH model at higher temperature. Room temperature magnetic measurements give the evidence of significant enhancement in magnetic properties with remanent magnetization (Mr = 0.1218 emu/g) and coercive field (Hc = 3.5342 kOe).

L-Tryptophan on Cu(111): engineering a molecular labyrinth driven by indole groups

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yitamben, E. N.; Clayborne, A.; Darling, Seth B.

2015-05-21

The present article investigates the adsorption and molecular orientation of L-Tryptophan, which is both an essential amino acid important for protein synthesis and of particular interest for the development of chiral molecular electronics and biocompatible processes and devices, on Cu(111) using scanning tunneling microscopy and spectroscopy at 55 K and at room temperature. The arrangement of chemisorbed L-Tryptophan on the copper surface varies with both temperature and surface coverage. At low coverage, small clusters form on the surface irrespective of temperature, while at high coverage an ordered chain structure emerges at room temperature, and a tightly packed structure forms amore » molecular labyrinth at low temperature. The dominating superstructure of the adsorbates arises from intermolecular hydrogen bonding, and pi-bonding interactions between the indole groups of neighboring molecules and the Cu surface.« less

Magnetic and dielectric behavior of chromium substituted Co-Mg ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Jadoun, Priya; Jyoti, Prashant, B. L.; Dolia, S. N.; Bhatnagar, D.; Saxena, V. K.

2016-05-01

The chromium doped Co-Mg ferrite with composition Co0.5Mg0.5Cr0.2Fe1.8O4 has been synthesized using sol-gel auto combustion method. The crystal structure has been analyzed by X-ray diffraction (XRD) technique. XRD pattern reveals the formation of single phase cubic spinel structure. The magnetic measurements show ferromagnetic behavior at room temperature and large coercivity is observed on cooling down the temperature to 20 K. Dielectric constant (ɛ') and dielectric loss tangent (tan δ) have been determined at room temperature as a function of frequency in the frequency range 75 kHz to 80 MHz. The decrease in dielectric constant with increasing frequency attributes to Maxwell Wagner model and conduction mechanism in ferrites.

TED Study of Si(113) Surfaces

NASA Astrophysics Data System (ADS)

Suzuki, T.; Minoda, H.; Tanishiro, Y.; Yagi, K.

A TED study of Si(113) surfaces was carried out. Reflections from the 3 × 2 reconstruction were seen at room temperature, while half-order reflections were very faint. The surface showed the phase transition between the 3 × 1 and the disordered (rough) structures at about 930°C. The (113) surface structure at room temperature was analyzed using TED intensity. Four kinds of structure models proposed previously, including both the 3 × 1 and the 3 × 2 reconstructed structures, were examined. The R-factors calculated using the energy-optimized atomic coordinates are not sufficiently small. After minimization of the R-factors, Dabrowski's 3 × 2 structure model is most agreeable, while Ranke's 3 × 1 and 3 × 2 structure models are not to be excluded. STM observation showed that the surface is composed of small domains of the 3 × 2 structure.

Sputter deposited titanium disilicide at high substrate temperatures

NASA Astrophysics Data System (ADS)

Tanielian, M.; Blackstone, S.; Lajos, R.

1984-08-01

Titanium disilicide films were sputter deposited from a composite TiSi2.1 target on <111> bare silicon wafers both at room temperature and at 600 °C. The room temperature as-deposited films require a 900 °C sintering step to reduce their resistivity. On the other hand, the as-deposited 600 °C films are fully reacted, polycrystalline, have no oxygen contamination, large grain sizes, and are oxidation resistant. Further annealing of these films at 900 °C produces no changes in their crystal structure, composition, resistivity, or grain size.

Optically induced strong intermodal coupling in mechanical resonators at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohta, R.; Okamoto, H.; Yamaguchi, H.

Strong parametric mode coupling in mechanical resonators is demonstrated at room temperature by using the photothermal effect in thin membrane structures. Thanks to the large stress modulation by laser irradiation, the coupling rate of the mechanical modes, defined as half of the mode splitting, reaches 2.94 kHz, which is an order of magnitude larger than electrically induced mode coupling. This large coupling rate exceeds the damping rates of the mechanical resonators and results in the strong coupling regime, which is a signature of coherent mode interaction. Room-temperature coherent mode coupling will enable us to manipulate mechanical motion at practical operation temperaturesmore » and provides a wide variety of applications of integrated mechanical systems.« less

Effect of treatment temperature on the microstructure of asphalt binders: insights on the development of dispersed domains.

PubMed

Menapace, I; Masad, E; Bhasin, A

2016-04-01

This paper offers important insights on the development of the microstructure in asphalt binders as a function of the treatment temperature. Different treatment temperatures are useful to understand how dispersed domains form when different driving energies for the mobility of molecular species are provided. Small and flat dispersed domains, with average diameter between 0.02 and 0.70 μm, were detected on the surface of two binders at room temperature, and these domains were observed to grow with an increase in treatment temperature (up to over 2 μm). Bee-like structures started to appear after treatment at or above 100°C. Moreover, the effect of the binder thickness on its microstructure at room temperature and at higher treatment temperatures was investigated and is discussed in this paper. At room temperature, the average size of the dispersed domains increased as the binder thickness decreased. A hypothesis that conciliates current theories on the origin and development of dispersed domains is proposed. Small dispersed domains (average diameter around 0.02 μm) are present in the bulk of the binder, whereas larger domains and bee-like structures develop on the surface, following heat treatment or mechanical disturbance that reduces the film thickness. Molecular mobility and association are the key factors in the development of binder microstructure. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001) Alloys.

PubMed

Lungu, George A; Apostol, Nicoleta G; Stoflea, Laura E; Costescu, Ruxandra M; Popescu, Dana G; Teodorescu, Cristian M

2013-02-21

Ferromagnetic Fe x Ge 1- x with x = 2%-9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 °C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 × 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe₃ to approximately FeGe₂, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics.

Advanced Control Surface Seal Development for Future Space Vehicles

NASA Technical Reports Server (NTRS)

DeMange, J. J.; Dunlap, P. H., Jr.; Steinetz, B. M.

2004-01-01

NASA s Glenn Research Center (GRC) has been developing advanced high temperature structural seals since the late 1980's and is currently developing seals for future space vehicles as part of the Next Generation Launch Technology (NGLT) program. This includes control surface seals that seal the edges and hinge lines of movable flaps and elevons on future reentry vehicles. In these applications, the seals must operate at temperatures above 2000 F in an oxidizing environment, limit hot gas leakage to protect underlying structures, endure high temperature scrubbing against rough surfaces, and remain flexible and resilient enough to stay in contact with sealing surfaces for multiple heating and loading cycles. For this study, three seal designs were compared against the baseline spring tube seal through a series of compression tests at room temperature and 2000 F and flow tests at room temperature. In addition, canted coil springs were tested as preloaders behind the seals at room temperature to assess their potential for improving resiliency. Addition of these preloader elements resulted in significant increases in resiliency compared to the seals by themselves and surpassed the performance of the baseline seal at room temperature. Flow tests demonstrated that the seal candidates with engineered cores had lower leakage rates than the baseline spring tube design. However, when the seals were placed on the preloader elements, the flow rates were higher as the seals were not compressed as much and therefore were not able to fill the groove as well. High temperature tests were also conducted to asses the compatibility of seal fabrics against ceramic matrix composite (CMC) panels anticipated for use in next generation launch vehicles. These evaluations demonstrated potential bonding issues between the Nextel fabrics and CMC candidates.

Toward Single Electron Nanoelectronics Using Self-Assembled DNA Structure.

PubMed

Tapio, Kosti; Leppiniemi, Jenni; Shen, Boxuan; Hytönen, Vesa P; Fritzsche, Wolfgang; Toppari, J Jussi

2016-11-09

DNA based structures offer an adaptable and robust way to develop customized nanostructures for various purposes in bionanotechnology. One main aim in this field is to develop a DNA nanobreadboard for a controllable attachment of nanoparticles or biomolecules to form specific nanoelectronic devices. Here we conjugate three gold nanoparticles on a defined size TX-tile assembly into a linear pattern to form nanometer scale isolated islands that could be utilized in a room temperature single electron transistor. To demonstrate this, conjugated structures were trapped using dielectrophoresis for current-voltage characterization. After trapping only high resistance behavior was observed. However, after extending the islands by chemical growth of gold, several structures exhibited Coulomb blockade behavior from 4.2 K up to room temperature, which gives a good indication that self-assembled DNA structures could be used for nanoelectronic patterning and single electron devices.

Role of an elliptical structure in photosynthetic energy transfer: Collaboration between quantum entanglement and thermal fluctuation

PubMed Central

Oka, Hisaki

2016-01-01

Recent experiments have revealed that the light-harvesting complex 1 (LH1) in purple photosynthetic bacteria has an elliptical structure. Generally, symmetry lowering in a structure leads to a decrease in quantum effects (quantum coherence and entanglement), which have recently been considered to play a role in photosynthetic energy transfer, and hence, elliptical structure seems to work against efficient photosynthetic energy transfer. Here we analyse the effect of an elliptical structure on energy transfer in a purple photosynthetic bacterium and reveal that the elliptical distortion rather enhances energy transfer from peripheral LH2 to LH1 at room temperature. Numerical results show that quantum entanglement between LH1 and LH2 is formed over a wider range of high energy levels than would have been the case with circular LH1. Light energy absorbed by LH2 is thermally pumped via thermal fluctuation and is effectively transferred to LH1 through the entangled states at room temperature rather than at low temperature. This result indicates the possibility that photosynthetic systems adopt an elliptical structure to effectively utilise both quantum entanglement and thermal fluctuation at physiological temperature. PMID:27173144

Role of an elliptical structure in photosynthetic energy transfer: Collaboration between quantum entanglement and thermal fluctuation

NASA Astrophysics Data System (ADS)

Oka, Hisaki

2016-05-01

Recent experiments have revealed that the light-harvesting complex 1 (LH1) in purple photosynthetic bacteria has an elliptical structure. Generally, symmetry lowering in a structure leads to a decrease in quantum effects (quantum coherence and entanglement), which have recently been considered to play a role in photosynthetic energy transfer, and hence, elliptical structure seems to work against efficient photosynthetic energy transfer. Here we analyse the effect of an elliptical structure on energy transfer in a purple photosynthetic bacterium and reveal that the elliptical distortion rather enhances energy transfer from peripheral LH2 to LH1 at room temperature. Numerical results show that quantum entanglement between LH1 and LH2 is formed over a wider range of high energy levels than would have been the case with circular LH1. Light energy absorbed by LH2 is thermally pumped via thermal fluctuation and is effectively transferred to LH1 through the entangled states at room temperature rather than at low temperature. This result indicates the possibility that photosynthetic systems adopt an elliptical structure to effectively utilise both quantum entanglement and thermal fluctuation at physiological temperature.

Role of an elliptical structure in photosynthetic energy transfer: Collaboration between quantum entanglement and thermal fluctuation.

PubMed

Oka, Hisaki

2016-05-13

Recent experiments have revealed that the light-harvesting complex 1 (LH1) in purple photosynthetic bacteria has an elliptical structure. Generally, symmetry lowering in a structure leads to a decrease in quantum effects (quantum coherence and entanglement), which have recently been considered to play a role in photosynthetic energy transfer, and hence, elliptical structure seems to work against efficient photosynthetic energy transfer. Here we analyse the effect of an elliptical structure on energy transfer in a purple photosynthetic bacterium and reveal that the elliptical distortion rather enhances energy transfer from peripheral LH2 to LH1 at room temperature. Numerical results show that quantum entanglement between LH1 and LH2 is formed over a wider range of high energy levels than would have been the case with circular LH1. Light energy absorbed by LH2 is thermally pumped via thermal fluctuation and is effectively transferred to LH1 through the entangled states at room temperature rather than at low temperature. This result indicates the possibility that photosynthetic systems adopt an elliptical structure to effectively utilise both quantum entanglement and thermal fluctuation at physiological temperature.

Crystal structures and high-temperature phase-transitions in SrNdMRuO{sub 6} (M=Zn,Co,Mg,Ni) new double perovskites studied by symmetry-mode analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iturbe-Zabalo, E., E-mail: iturbe@ill.fr; Fisika Aplikatua II Saila, Zientzia eta Teknologia Fakultatea, UPV/EHU, P.O. Box 644, 48080 Bilbao; Igartua, J.M.

2013-02-15

Crystal structures of SrNdZnRuO{sub 6}, SrNdCoRuO{sub 6}, SrNdMgRuO{sub 6} and SrNdNiRuO{sub 6} double perovskites have been studied by X-ray, synchrotron radiation and neutron powder diffraction method, at different temperatures, and using the symmetry-mode analysis. All compounds adopt the monoclinic space group P2{sub 1}/n at room-temperature, and contain a completely ordered array of the tilted MO{sub 6} and RuO{sub 6} octahedra, whereas Sr/Nd cations are completely disordered. The analysis of the structures in terms of symmetry-adapted modes of the parent phase allows the identification of the modes responsible for the phase-transition. The high-temperature study (300-1250 K) has shown that the compoundsmore » present a temperature induced structural phase-transition: P2{sub 1}/n{yields}P4{sub 2}/n{yields}Fm3{sup Macron }m. - Graphical abstract: Representation of the dominant distortion modes of the symmetry mode decomposition of the room-temperature (P2{sub 1}/n), intermediate (P4{sub 2}/n) and cubic (Fm-3m) phase SrNdMRuO{sub 6} (M=Zn,Co,Mg,Ni), with respect to the parent phase Fm-3m. The dominant distortion modes are: in the monoclinic phase-GM{sub 4}{sup +} (blue arrow), X{sub 3}{sup +} (green arrow) and X{sub 5}{sup +} acting on A-site cations (red arrow); in the tetragonal phase-GM{sub 4}{sup +} (pink arrow), X{sub 3}{sup +} (light blue arrow) and X{sub 5}{sup +} acting on A-site cations (brown arrow). Highlights: Black-Right-Pointing-Pointer Structural study of four ruthenate double perovskites. Black-Right-Pointing-Pointer Room-temperature structural determination using symmetry-mode procedure. Black-Right-Pointing-Pointer Determination of temperature induced structural phase-transitions. Black-Right-Pointing-Pointer Symmetry adapted-mode analysis.« less

Observation of Wakefield Suppression in a Photonic-Band-Gap Accelerator Structure

DOE PAGES

Simakov, Evgenya I.; Arsenyev, Sergey A.; Buechler, Cynthia E.; ...

2016-02-10

We report experimental observation of higher order mode (HOM) wakefield suppression in a room-temperature traveling-wave photonic band gap (PBG) accelerating structure at 11.700 GHz. It has been long recognized that PBG structures have potential for reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in a room-temperature PBG structure was conducted in 2005. Since then, the importance of PBG accelerator research has been recognized by many institutions. However, the full experimental characterization of the wakefield spectrum and demonstration of wakefield suppression when the accelerating structure is excited by an electron beam has not been performed to date. Wemore » conducted an experiment at the Argonne Wakefield Accelerator (AWA) test facility and observed wakefields excited by a single high charge electron bunch when it passes through a PBG accelerator structure. Lastly, excellent HOM suppression properties of the PBG accelerator were demonstrated in the beam test.« less

Tungsten Inert Gas and Friction Stir Welding Characteristics of 4-mm-Thick 2219-T87 Plates at Room Temperature and -196 °C

NASA Astrophysics Data System (ADS)

Lei, Xuefeng; Deng, Ying; Yin, Zhimin; Xu, Guofu

2014-06-01

2219-T87 aluminum alloy is widely used for fabricating liquid rocket propellant storage tank, due to its admirable cryogenic property. Welding is the dominant joining method in the manufacturing process of aerospace components. In this study, the tungsten inert gas welding and friction stir welding (FSW) characteristics of 4-mm-thick 2219-T87 alloy plate at room temperature (25 °C) and deep cryogenic temperature (-196 °C) were investigated by property measurements and microscopy methods. The studied 2219 base alloy exhibits a low strength plane anisotropy and excellent room temperature and cryogenic mechanical properties. The ultimate tensile strength values of TIG and FSW welding joints can reach 265 and 353 MPa at room temperature, and 342 and 438 MPa at -196 °C, respectively. The base metal consists of elongated deformed grains and many nano-scaled θ (Al2Cu) aging precipitates. Fusion zone and heat-affected zone (HAZ) of the TIG joint are characterized by coarsening dendritic grains and equiaxed recrystallized grains, respectively. The FSW-welded joint consists of the weld nugget zone, thermo-mechanically affected zone (TMAZ), and HAZ. In the weld nugget zone, a micro-scaled sub-grain structure is the main microstructure characteristic. The TMAZ and HAZ are both characterized by coarsened aging precipitates and elongated deformed grains. The excellent FSW welding properties are attributed to the preservation of the working structures and homogenous chemical compositions.

Ab initio structure determination of nanocrystals of organic pharmaceutical compounds by electron diffraction at room temperature using a Timepix quantum area direct electron detector

PubMed Central

van Genderen, E.; Clabbers, M. T. B.; Das, P. P.; Stewart, A.; Nederlof, I.; Barentsen, K. C.; Portillo, Q.; Pannu, N. S.; Nicolopoulos, S.; Gruene, T.; Abrahams, J. P.

2016-01-01

Until recently, structure determination by transmission electron microscopy of beam-sensitive three-dimensional nanocrystals required electron diffraction tomography data collection at liquid-nitrogen temperature, in order to reduce radiation damage. Here it is shown that the novel Timepix detector combines a high dynamic range with a very high signal-to-noise ratio and single-electron sensitivity, enabling ab initio phasing of beam-sensitive organic compounds. Low-dose electron diffraction data (∼0.013 e− Å−2 s−1) were collected at room temperature with the rotation method. It was ascertained that the data were of sufficient quality for structure solution using direct methods using software developed for X-ray crystallography (XDS, SHELX) and for electron crystallography (ADT3D/PETS, SIR2014). PMID:26919375

15N NMR study of nitrate ion structure and dynamics in hydrotalcite-like compounds

USGS Publications Warehouse

Hou, X.; James, Kirkpatrick R.; Yu, P.; Moore, D.; Kim, Y.

2000-01-01

We report here the first nuclear magnetic resonance (NMR) spectroscopic study of the dynamical and structural behavior of nitrate on the surface and in the interlayer of hydrotalcite-like compounds (15NO3--HT). Spectroscopically resolvable surface-absorbed and interlayer NO3- have dramatically different dynamical characteristics. The interlayer nitrate shows a well defined, temperature independent uniaxial chemical shift anisotropy (CS A) powder pattern. It is rigidly held or perhaps undergoes rotation about its threefold axis at all temperatures between -100 ??C and +80 ??C and relative humidities (R.H.) from 0 to 100% at room temperature. For surface nitrate, however, the dynamical behavior depends substantially on temperature and relative humidity. Analysis of the temperature and R.H. dependences of the peak width yields reorieritational frequencies which increase from essentially 0 at -100 ??C to 2.6 ?? 105 Hz at 60 ??C and an activation energy of 12.6 kJ/mol. For example, for samples at R.H. = 33%, the surface nitrate is isotropically mobile at frequencies greater than 105 Hz at room temperature, but it becomes rigid or only rotates on its threefold axis at -100 ??C. For dry samples and samples heated at 200 ??C (R.H. near 0%), the surface nitrate is not isotropically averaged at room temperature. In contrast to our previous results for 35Cl--containing hydrotalcite (35Cl--HT), no NMR detectable structural phase transition is observed for 15NO3--HT. The mobility of interlayer nitrate in HT is intermediate between that of carbonate and chloride.

Preparation of Sm-doped ceria (SDC) nanowires and tubes by gas-liquid co-precipitation at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gu Lina; School of Chemistry and Chemical Engineering, Anhui University, 230039 Hefei; Meng Guangyao

Sm-doped cerium dioxide (SDC) with fcc structure was formed using a gas-liquid chemical co-precipitation process at room temperature. Morphology and structure of the as-prepared samples were characterized using TG, XRD, TEM, HRTEM and SAED techniques. Under our specific experimental conditions, two kinds of 1D nano-structures SDC have been mainly obtained. SDC nanowires are 0.3-1.2 {mu}m in lengths and 5-20 nm in diameters. SDC nanotubes have outer diameters in 10-40 nm with lengths up to 2 {mu}m. The as-prepared SDC shows very strong UV absorption ability and the maximum absorption peak redshifts compared with that of SDC nanoparticles.

Room temperature ferromagnetism in non-magnetic doped TiO2 nanoparticles

NASA Astrophysics Data System (ADS)

Gómez-Polo, C.; Larumbe, S.; Pastor, J. M.

2013-05-01

Room-temperature ferromagnetism in non-magnetic doped TiO2 semiconductor nanoparticles is analyzed in the present work. Undoped and N-doped TiO2 nanoparticles were obtained employing sol-gel procedure using urea as the nitrogen source. The obtained gels were first dried at 70 °C and afterwards calcined in air at 300 °C. A residual carbon concentration was retained in the samples as a consequence of the organic decomposition process. Post-annealing treatments at 300 °C under air and vacuum conditions were also performed. The crystallographic structure of nanoparticles was analyzed by X-ray diffraction, obtaining a single anatase crystalline phase after the calcinations (mean nanoparticle diameters around 5-8 nm). SQUID magnetometry was employed to analyze the magnetic response of the samples. Whereas for the undoped samples synthesized with hydrolysis rate h = 6, paramagnetic like behavior is observed at room temperature, the N-doped nanoparticles (h = 3) show a weak ferromagnetic response (saturation magnetization ≈10-3 emu/g). Moreover, a clear reinforcement of the room-temperature ferromagnetism response is found with the post-annealing treatments, in particular that performed in vacuum. Thus, the results indicate the dominant role of the oxygen stoichiometry and the oxygen vacancies in the room temperature ferromagnetic response of these TiO2 nanoparticles.

UV-light-assisted ethanol sensing characteristics of g-C3N4/ZnO composites at room temperature

NASA Astrophysics Data System (ADS)

Zhai, Jiali; Wang, Tao; Wang, Chuang; Liu, Dechen

2018-05-01

A highly efficient UV-light-assisted room temperature sensor based on g-C3N4/ZnO composites were prepared by an in situ precipitation method. The thermostability, composition, structure, and morphology properties of the as-prepared g-C3N4/ZnO composites were characterized by TGA, XRD, FT-IR, TEM, and XPS, respectively. And then, we studied the ethanol (C2H5OH) sensing performance of the g-C3N4/ZnO composites at the room temperature. Compared with pure ZnO and g-C3N4, the gas sensing activity of g-C3N4/ZnO composites was greatly improved at room temperature, for example, the g-C3N4/ZnO-8% composites showed an obvious response of 121-40 ppm C2H5OH at room temperature, which was 60 times higher than the pure ZnO based on the sensors under the same condition. The great enhancement of the C2H5OH sensing properties of composites can be understood by the efficient separation of photogenerated charge carriers of g-C3N4/ZnO heterogeneous and the UV-light catalytic effect. Finally, a possible mechanism for the gas sensing activity was proposed.

Preliminary metallographic studies of ball fatigue under rolling-contact conditions

NASA Technical Reports Server (NTRS)

Bear, H Robert; Butler, Robert H

1957-01-01

The metallurgical results produced on balls tested in the rolling-contact fatigue spin rig were studied by metallographic examination. Origin and progression of fatigue failures were observed. These evaluations were made on SAE 52100 and AISI M-1 balls fatigue tested at room temperature (80 F) and 200 to 250 F. Most failures originated subsurface in shear; inclusions, structure changes, and directionalism adversely affected ball fatigue life. Structures in the maximum-shear-stress region of the balls of both materials were stable at room temperature and unstable at 200 to 250 F. Failures were of the same type as those found in full-scale bearings.

Defect free C-axis oriented zinc oxide (ZnO) films grown at room temperature using RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Kunj, Saurabh; Sreenivas, K.

2016-05-01

Radio frequency Magnetron sputtering technique was employed to fabricate ZnO thin films on quartz substrate at room temperature. The effect of varying oxygen to argon (O2/Ar) gas ratio on the structural and photoluminescence properties of the film is analyzed.X-ray diffraction (XRD) spectra reveals the formation of hexagonal wurtzite structured ZnO thin films with preferred orientation along (002) plane. Photoluminescence (PL) characterization reveals the preparation of highly crystalline films exhibiting intense Ultraviolet (UV) emission with negligible amount of defects as indicated by the absence of Deep Level Emission (DLE) in the PL spectra.

Defect free C-axis oriented zinc oxide (ZnO) films grown at room temperature using RF magnetron sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kunj, Saurabh, E-mail: saurabhkunj22@gmail.com; Sreenivas, K.

2016-05-23

Radio frequency Magnetron sputtering technique was employed to fabricate ZnO thin films on quartz substrate at room temperature. The effect of varying oxygen to argon (O{sub 2}/Ar) gas ratio on the structural and photoluminescence properties of the film is analyzed.X-ray diffraction (XRD) spectra reveals the formation of hexagonal wurtzite structured ZnO thin films with preferred orientation along (002) plane. Photoluminescence (PL) characterization reveals the preparation of highly crystalline films exhibiting intense Ultraviolet (UV) emission with negligible amount of defects as indicated by the absence of Deep Level Emission (DLE) in the PL spectra.

Room temperature continuous wave mid-infrared VCSEL operating at 3.35 μm

NASA Astrophysics Data System (ADS)

Jayaraman, V.; Segal, S.; Lascola, K.; Burgner, C.; Towner, F.; Cazabat, A.; Cole, G. D.; Follman, D.; Heu, P.; Deutsch, C.

2018-02-01

Tunable vertical cavity surface emitting lasers (VCSELs) offer a potentially low cost tunable optical source in the 3-5 μm range that will enable commercial spectroscopic sensing of numerous environmentally and industrially important gases including methane, ethane, nitrous oxide, and carbon monoxide. Thus far, achieving room temperature continuous wave (RTCW) VCSEL operation at wavelengths beyond 3 μm has remained an elusive goal. In this paper, we introduce a new device structure that has enabled RTCW VCSEL operation near the methane absorption lines at 3.35 μm. This device structure employs two GaAs/AlGaAs mirrors wafer-bonded to an optically pumped active region comprising compressively strained type-I InGaAsSb quantum wells grown on a GaSb substrate. This substrate is removed in processing, as is one of the GaAs mirror substrates. The VCSEL structure is optically pumped at room temperature with a CW 1550 nm laser through the GaAs substrate, while the emitted 3.3 μm light is captured out of the top of the device. Power and spectrum shape measured as a function of pump power exhibit clear threshold behavior and robust singlemode spectra.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aparnadevi, N.; Department of Nuclear Physics, University of Madras, Guindy Campus, Chennai 600 025; Saravana Kumar, K.

Phase pure NdFeO{sub 3} has been achieved using high energy ball milling of oxide precursors with subsequent sintering. It is established that structural arrangement of NdFeO{sub 3} regulates the multifunctional feature of the material. Rietveld refinement of the room temperature X-ray diffraction pattern shows that the Fe-O-Fe bond angle significantly favors the super exchange interaction, which is predominantly antiferromagnetic in nature. Magnetization measurement illustrates antiferromagnetic behaviour with a weak ferromagnetic component caused by the canted nature of the Fe{sup 3+} spins at room temperature. Absorption bands in the visible ambit, apparent from the UV-Vis diffuse reflectance studies, is found duemore » to the crystal ligand field of octahedral oxygen environment of Fe{sup 3+} ions. The direct band gap is estimated to be 2.39 eV from the diffuse reflectance spectrum. The lossy natured ferroelectric loop having a maximum polarization of 0.23 μC/cm{sup 2} at room temperature is found to be driven by the non-collinear magnetic structure with reverse Dzyaloshinskii–Moriya effect. Magnetic field has influence on the dielectric constant as evident from the impedance spectroscopy, indicating the strong coupling between ferroelectric and the magnetic structure of NdFeO{sub 3}.« less

Continuous-wave mid-infrared photonic crystal light emitters at room temperature

NASA Astrophysics Data System (ADS)

Weng, Binbin; Qiu, Jijun; Shi, Zhisheng

2017-01-01

Mid-infrared photonic crystal enhanced lead-salt light emitters operating under continuous-wave mode at room temperature were investigated in this work. For the device, an active region consisting of 9 pairs of PbSe/Pb0.96Sr0.04Se quantum wells was grown by molecular beam epitaxy method on top of a Si(111) substrate which was initially dry-etched with a two-dimensional photonic crystal structure in a pattern of hexagonal holes. Because of the photonic crystal structure, an optical band gap between 3.49 and 3.58 µm was formed, which matched with the light emission spectrum of the quantum wells at room temperature. As a result, under optical pumping, using a near-infrared continuous-wave semiconductor laser, the device exhibited strong photonic crystal band-edge mode emissions and delivered over 26.5 times higher emission efficiency compared to the one without photonic crystal structure. The output power obtained was up to 7.68 mW (the corresponding power density was 363 mW/cm2), and a maximum quantum efficiency reached to 1.2%. Such photonic crystal emitters can be used as promising light sources for novel miniaturized gas-sensing systems.

Superior room-temperature ductility of typically brittle quasicrystals at small sizes

PubMed Central

Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph

2016-01-01

The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of ∼4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals—dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices. PMID:27515779

Crystal cryocooling distorts conformational heterogeneity in a model Michaelis complex of DHFR

PubMed Central

Keedy, Daniel A.; van den Bedem, Henry; Sivak, David A.; Petsko, Gregory A.; Ringe, Dagmar; Wilson, Mark A.; Fraser, James S.

2014-01-01

Summary Most macromolecular X-ray structures are determined from cryocooled crystals, but it is unclear whether cryocooling distorts functionally relevant flexibility. Here we compare independently acquired pairs of high-resolution datasets of a model Michaelis complex of dihydrofolate reductase (DHFR), collected by separate groups at both room and cryogenic temperatures. These datasets allow us to isolate the differences between experimental procedures and between temperatures. Our analyses of multiconformer models and time-averaged ensembles suggest that cryocooling suppresses and otherwise modifies sidechain and mainchain conformational heterogeneity, quenching dynamic contact networks. Despite some idiosyncratic differences, most changes from room temperature to cryogenic temperature are conserved, and likely reflect temperature-dependent solvent remodeling. Both cryogenic datasets point to additional conformations not evident in the corresponding room-temperature datasets, suggesting that cryocooling does not merely trap pre-existing conformational heterogeneity. Our results demonstrate that crystal cryocooling consistently distorts the energy landscape of DHFR, a paragon for understanding functional protein dynamics. PMID:24882744

Red Phosphorescence from Benzo[2,1,3]thiadiazoles at Room Temperature.

PubMed

Gutierrez, Gregory D; Sazama, Graham T; Wu, Tony; Baldo, Marc A; Swager, Timothy M

2016-06-03

We describe the red phosphorescence exhibited by a class of structurally simple benzo[2,1,3]thiadiazoles at room temperature. The photophysical properties of these molecules in deoxygenated cyclohexane, including their absorption spectra, steady-state photoluminescence and excitation spectra, and phosphorescence lifetimes, are presented. Time-dependent density functional theory calculations were carried out to better understand the electronic excited states of these benzo[2,1,3]thiadiazoles and why they are capable of phosphorescence.

Material design of two-phase-coexisting niobate dielectrics by electrostatic adsorption

NASA Astrophysics Data System (ADS)

Fuchigami, Teruaki; Yoshida, Katsuya; Kakimoto, Ken-ichi

2017-10-01

A material design process using electrostatic adsorption was proposed to synthesize composite ceramics with a two-phase-coexisting structure. Supported particles were fabricated by the electrostatic adsorption of (Na,K)NbO3-SrTiO3 (NKN-ST) nanoparticles on (Na,K)NbO3-Ba2NaNb5O15 (NKN-BNN) particles. NKN-ST and NKN-BNN were well dispersed with no aggregate in NKN-ST/NKN-BNN ceramics synthesized using the supported particles in comparison with ceramics synthesized using a mixture obtained by simply mixing NKN-ST and NKN-BNN powder. The temperature dependence of dielectric constant is closely related to the composite structure and the dielectric constant was stable in a wide temperature range from room temperature to 400 °C. Capacitance for DC bias was also insensitive to temperature in the range of 0-2 kV/mm, and the change rate of the capacitance was within ±5% in the temperature range from room temperature to 200 °C.

Electric field control of ferromagnetism at room temperature in GaCrN (p-i-n) device structures

NASA Astrophysics Data System (ADS)

El-Masry, N. A.; Zavada, J. M.; Reynolds, J. G.; Reynolds, C. L.; Liu, Z.; Bedair, S. M.

2017-08-01

We have demonstrated a room temperature dilute magnetic semiconductor based on GaCrN epitaxial layers grown by metalorganic chemical vapor deposition. Saturation magnetization Ms increased when the GaCrN film is incorporated into a (p-GaN/i-GaCrN/n-GaN) device structure, due to the proximity of mediated holes present in the p-GaN layer. Zero field cooling and field cooling were measured to ascertain the absence of superparamagnetic behavior in the films. A (p-GaN/i-GaCrN/n-GaN) device structure with room temperature ferromagnetic (FM) properties that can be controlled by an external applied voltage has been fabricated. In this work, we show that the applied voltage controls the ferromagnetic properties, by biasing the (p-i-n) structure. With forward bias, ferromagnetism in the GaCrN layer was increased nearly 4 fold of the original value. Such an enhancement is due to carrier injection of holes into the Cr deep level present in the i-GaCrN layer. A "memory effect" for the FM behavior of the (p-i-n) GaCrN device structure persisted for 42 h after the voltage bias was turned off. These measurements also support that the observed ferromagnetism in the GaCrN film is not due to superparamagnetic clusters but instead is a hole-mediated phenomenon.

Electromagnetic interference shielding performance of nano-layered Ti3SiC2 ceramics at high-temperatures

NASA Astrophysics Data System (ADS)

Li, Sigong; Tan, Yongqiang; Xue, Jiaxiang; Liu, Tong; Zhou, Xiaosong; Zhang, Haibin

2018-01-01

The X-band electromagnetic interference (EMI) shielding properties of nano-layered Ti3SiC2 ceramics were evaluated from room temperature up to 800°C in order to explore the feasibility of Ti3SiC2 as efficient high temperature EMI shielding material. It was found that Ti3SiC2 exhibits satisfactory EMI shielding effectiveness (SE) close to 30 dB at room temperature and the EMI SE shows good temperature stability. The remarkable EMI shielding properties of Ti3SiC2 can be mainly attributed to high electrical conductivity, high dielectric loss and more importantly the multiple reflections due to the layered structure.

VO{sub 2} (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rao Popuri, Srinivasa; University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac; National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara

2014-05-01

Well crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal reaction in the presence of V{sub 2}O{sub 5} and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO{sub 2} (A) micro rods. The structural and electronic transitions in VO{sub 2} (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversiblemore » intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO{sub 2} (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO{sub 2} (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO{sub 2} (M1) are described. - Graphical abstract: Using a single step and template free hydrothermal synthesis, well crystallized VO{sub 2} (A) microrods were prepared and the P4/ncc space group was assigned to the room temperature crystal structure. Reversible and irreversible phase transitions among different VO{sub 2} polymorphs were identified and their progressive nature was highlighted. Attempts to increase the microrods size, involving layer by layer formation mechanisms, are presented. - Highlights: • Highly crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal process. • The P4/ncc space group was determined for VO{sub 2} (A) at room temperature. • The electronic structure and progressive nature of the structural phase transition were investigated. • A weak coupling between structural and electronic phase transitions was identified. • Different crystallite morphologies were discussed in relation with growth mechanisms.« less

Fast detection and low power hydrogen sensor using edge-oriented vertically aligned 3-D network of MoS2 flakes at room temperature

NASA Astrophysics Data System (ADS)

Agrawal, A. V.; Kumar, R.; Venkatesan, S.; Zakhidov, A.; Zhu, Z.; Bao, Jiming; Kumar, Mahesh; Kumar, Mukesh

2017-08-01

The increased usage of hydrogen as a next generation clean fuel strongly demands the parallel development of room temperature and low power hydrogen sensors for their safety operation. In this work, we report strong evidence for preferential hydrogen adsorption at edge-sites in an edge oriented vertically aligned 3-D network of MoS2 flakes at room temperature. The vertically aligned edge-oriented MoS2 flakes were synthesised by a modified CVD process on a SiO2/Si substrate and confirmed by Scanning Electron Microscopy. Raman spectroscopy and PL spectroscopy reveal the signature of few-layer MoS2 flakes in the sample. The sensor's performance was tested from room temperature to 150 °C for 1% hydrogen concentration. The device shows a fast response of 14.3 s even at room temperature. The sensitivity of the device strongly depends on temperature and increases from ˜1% to ˜11% as temperature increases. A detail hydrogen sensing mechanism was proposed based on the preferential hydrogen adsorption at MoS2 edge sites. The proposed gas sensing mechanism was verified by depositing ˜2-3 nm of ZnO on top of the MoS2 flakes that partially passivated the edge sites. We found a decrease in the relative response of MoS2-ZnO hybrid structures. This study provides a strong experimental evidence for the role of MoS2 edge-sites in the fast hydrogen sensing and a step closer towards room temperature, low power (0.3 mW), hydrogen sensor development.

Neutron powder diffraction refinement of the nuclear and magnetic structures of HoNi{sub 2}B{sub 2}C at R.T., 10, 5.1, and 2.2 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Q.; Grigereit, T.E.; Lynn, J.W.

The nuclear and magnetic structures of HoNi{sub 2}B{sub 2}C have been investigated by neutron powder diffraction at room temperature and at 10, 5.1 and 2.2K. The compound crystallizes with the symmetry of space group 14/mmm and has room temperature lattice parameters a = 3.5170(1) and c = 10.5217(3) {angstrom}. No phase transitions of the nuclear structure have been observed in the range of temperatures examined. Magnetic peaks begin to appear at about 8K. The magnetic structure is the superposition of two configurations, one in which ferromagnetic sheets of holmium spins parallel to the a-b plane are coupled antiferromagnetically along themore » c-axis, and another in which the ferromagnetic planes are rotated away from the antiparallel configuration to give an incommensurate helicoidal structure with a period approximately equal to twelve times the length of the c-axis. The helicoidal structure competes with superconductivity while the antiferromagnetism coexists with it.« less

Toward hydrogen detection at room temperature with printed ZnO nanoceramics films activated with halogen lighting

NASA Astrophysics Data System (ADS)

Nguyen, Van Son; Jubera, Véronique; Garcia, Alain; Debéda, Hélène

2015-12-01

Though semiconducting properties of ZnO have been extensively investigated under hazardous gases, research is still necessary for low-cost sensors working at room temperature. Study of printed ZnO nanopowders-based sensors has been undertaken for hydrogen detection. A ZnO paste made with commercial nanopowders is deposited onto interdigitated Pt electrodes and sintered at 400 °C. The ZnO layer structure and morphology are first examined by XRD, SEM, AFM and emission/excitation spectra prior to the study of the effect of UV-light on the electrical conduction of the semiconductor oxide. The response to hydrogen exposure is subsequently examined, showing that low UV-light provided by halogen lighting enhances the gas response and allows detection at room temperature with gas responses similar to those obtained in dark conditions at 150 °C. A gas response of 44% (relative change in current) under 300 ppm is obtained at room temperature. Moreover, it is demonstrated that very low UV-light power (15 μW/mm2) provided by the halogen lamp is sufficient to give sensitivities as high as those for much higher powers obtained with a UV LED (7.7 mW/mm2). These results are comparable to those obtained by others for 1D or 2D ZnO nanostructures working at room temperature or at temperatures up to 250 °C.

Highly selective room temperature NO2 gas sensor based on rGO-ZnO composite

NASA Astrophysics Data System (ADS)

Jyoti, Kanaujiya, Neha; Varma, G. D.

2018-05-01

Blending metal oxide nanoparticles with graphene or its derivatives can greatly enhance gas sensing characteristics. In the present work, ZnO nanoparticles have been synthesized via reflux method. Thin films of reduced graphene oxide (rGO) and composite of rGO-ZnO have been fabricated by drop casting method for gas sensing application. The samples have been characterized by X-ray diffraction (XRD) and Field-emission scanning electron microscope (FESEM) for the structural and morphological studies respectively. Sensing measurements have been carried out for the composite film of rGO-ZnO for different concentrations of NO2 ranging from 4 to 100 ppm. Effect of increasing temperature on the sensing performance has also been studied and the rGO-ZnO composite sensor shows maximum percentage response at room temperature. The limit of detection (LOD) for rGO-ZnO composite sensor is 4ppm and it exhibits a high response of 48.4% for 40 ppm NO2 at room temperature. To check the selectivity of the composite sensor, sensor film has been exposed to 40 ppm different gases like CO, NH3, H2S and Cl2 at room temperature and the sensor respond negligibly to these gases. The present work suggests that rGO-ZnO composite material can be a better candidate for fabrication of highly selective room temperature NO2 gas sensor.

Self-generated Local Heating Induced Nanojoining for Room Temperature Pressureless Flexible Electronic Packaging

PubMed Central

Peng, Peng; Hu, Anming; Gerlich, Adrian P.; Liu, Yangai; Zhou, Y. Norman

2015-01-01

Metallic bonding at an interface is determined by the application of heat and/or pressure. The means by which these are applied are the most critical for joining nanoscale structures. The present study considers the feasibility of room-temperature pressureless joining of copper wires using water-based silver nanowire paste. A novel mechanism of self-generated local heating within the silver nanowire paste and copper substrate system promotes the joining of silver-to-silver and silver-to-copper without any external energy input. The localized heat energy was delivered in-situ to the interfaces to promote atomic diffusion and metallic bond formation with the bulk component temperature stays near room-temperature. This local heating effect has been detected experimentally and confirmed by calculation. The joints formed at room-temperature without pressure achieve a tensile strength of 5.7 MPa and exhibit ultra-low resistivity in the range of 101.3 nOhm·m. The good conductivity of the joint is attributed to the removal of organic compounds in the paste and metallic bonding of silver-to-copper and silver-to-silver. The water-based silver nanowire paste filler material is successfully applied to various flexible substrates for room temperature bonding. The use of chemically generated local heating may become a potential method for energy in-situ delivery at micro/nanoscale. PMID:25788019

Potential of energy harvesting in barium titanate based laminates from room temperature to cryogenic/high temperatures: measurements and linking phase field and finite element simulations

NASA Astrophysics Data System (ADS)

Narita, Fumio; Fox, Marina; Mori, Kotaro; Takeuchi, Hiroki; Kobayashi, Takuya; Omote, Kenji

2017-11-01

This paper studies the energy harvesting characteristics of piezoelectric laminates consisting of barium titanate (BaTiO3) and copper (Cu) from room temperature to cryogenic/high temperatures both experimentally and numerically. First, the output voltages of the piezoelectric BaTiO3/Cu laminates were measured from room temperature to a cryogenic temperature (77 K). The output power was evaluated for various values of load resistance. The results showed that the maximum output power density is approximately 2240 nW cm-3. The output voltages of the BaTiO3/Cu laminates were also measured from room temperature to a higher temperature (333 K). To discuss the output voltages of the BaTiO3/Cu laminates due to temperature changes, phase field and finite element simulations were combined. A phase field model for grain growth was used to generate grain structures. The phase field model was then employed for BaTiO3 polycrystals, coupled with the time-dependent Ginzburg-Landau theory and the oxygen vacancies diffusion, to calculate the temperature-dependent piezoelectric coefficient and permittivity. Using these properties, the output voltages of the BaTiO3/Cu laminates from room temperature to both 77 K and 333 K were analyzed by three dimensional finite element methods, and the results are presented for several grain sizes and oxygen vacancy densities. It was found that electricity in the BaTiO3 ceramic layer is generated not only through the piezoelectric effect caused by a thermally induced bending stress but also by the temperature dependence of the BaTiO3 piezoelectric coefficient and permittivity.

Understanding local degradation of cycled Ni-rich cathode materials at high operating temperature for Li-ion batteries

NASA Astrophysics Data System (ADS)

Hwang, Sooyeon; Kim, Dong Hyun; Chung, Kyung Yoon; Chang, Wonyoung

2014-09-01

We utilize transmission electron microscopy in conjunction with electron energy loss spectroscopy to investigate local degradation that occurs in LixNi0.8Co0.15Al0.05O2 cathode materials (NCA) after 30 cycles with cutoff voltages of 4.3 V and 4.8 V at 55 °C. NCA has a homogeneous crystallographic structure before electrochemical reactions; however, we observed that 30 cycles of charge/discharge reactions induced inhomogeneity in the crystallographic and electronic structures and also introduced porosity particularly at surface area. These changes were more noticeable in samples cycled with higher cutoff voltage of 4.8 V. Effect of operating temperature was further examined by comparing electronic structures of oxygen of the NCA particles cycled at both room temperature and 55 °C. The working temperature has a greater impact on the NCA cathode materials at a cutoff voltage of 4.3 V that is the practical the upper limit voltage in most applications, while a cutoff voltage of 4.8 V is high enough to cause surface degradation even at room temperature.

Hydrogen-induced morphotropic phase transformation of single-crystalline vanadium dioxide nanobeams.

PubMed

Hong, Woong-Ki; Park, Jong Bae; Yoon, Jongwon; Kim, Bong-Joong; Sohn, Jung Inn; Lee, Young Boo; Bae, Tae-Sung; Chang, Sung-Jin; Huh, Yun Suk; Son, Byoungchul; Stach, Eric A; Lee, Takhee; Welland, Mark E

2013-04-10

We report a morphotropic phase transformation in vanadium dioxide (VO2) nanobeams annealed in a high-pressure hydrogen gas, which leads to the stabilization of metallic phases. Structural analyses show that the annealed VO2 nanobeams are hexagonal-close-packed structures with roughened surfaces at room temperature, unlike as-grown VO2 nanobeams with the monoclinic structure and with clean surfaces. Quantitative chemical examination reveals that the hydrogen significantly reduces oxygen in the nanobeams with characteristic nonlinear reduction kinetics which depend on the annealing time. Surprisingly, the work function and the electrical resistance of the reduced nanobeams follow a similar trend to the compositional variation due mainly to the oxygen-deficiency-related defects formed at the roughened surfaces. The electronic transport characteristics indicate that the reduced nanobeams are metallic over a large range of temperatures (room temperature to 383 K). Our results demonstrate the interplay between oxygen deficiency and structural/electronic phase transitions, with implications for engineering electronic properties in vanadium oxide systems.

Multiferroic properties and structural features of M-type Al-substituted barium hexaferrites

NASA Astrophysics Data System (ADS)

Trukhanov, A. V.; Trukhanov, S. V.; Kostishin, V. G.; Panina, L. V.; Salem, M. M.; Kazakevich, I. S.; Turchenko, V. A.; Kochervinskii, V. V.; Krivchenya, D. A.

2017-04-01

Precise studies of the crystal and magnetic structures of M-type substituted barium hexaferrites BaFe12- x Al x O19 (0.1 ≤ x ≤ 1.2) have been performed by powder neutron diffraction in the temperature range 300-730 K. The electric polarization and the magnetization, and also the magnetoelectric effect of the compositions under study have been studied in electric (to 110 kV/m) and magnetic (to 14 T) fields at room temperature. The spontaneous polarization and significant correlation between the dielectric and magnetic subsystems have been observed at room temperature. The magnetoelectric effect value is, on average, about 5%, and it increases slightly with the aluminum cation concentration. The precise structural studies made it possible to reveal the cause and the mechanism of formation of the spontaneous polarization in M-type substituted barium hexaferrites BaFe12- x Al x O19 ( x ≤ 1.2) with a collinear ferromagnetic structure.

Strong-coupling of WSe2 in ultra-compact plasmonic nanocavities at room temperature.

PubMed

Kleemann, Marie-Elena; Chikkaraddy, Rohit; Alexeev, Evgeny M; Kos, Dean; Carnegie, Cloudy; Deacon, Will; de Pury, Alex Casalis; Große, Christoph; de Nijs, Bart; Mertens, Jan; Tartakovskii, Alexander I; Baumberg, Jeremy J

2017-11-03

Strong coupling of monolayer metal dichalcogenide semiconductors with light offers encouraging prospects for realistic exciton devices at room temperature. However, the nature of this coupling depends extremely sensitively on the optical confinement and the orientation of electronic dipoles and fields. Here, we show how plasmon strong coupling can be achieved in compact, robust, and easily assembled gold nano-gap resonators at room temperature. We prove that strong-coupling is impossible with monolayers due to the large exciton coherence size, but resolve clear anti-crossings for greater than 7 layer devices with Rabi splittings exceeding 135 meV. We show that such structures improve on prospects for nonlinear exciton functionalities by at least 10 4 , while retaining quantum efficiencies above 50%, and demonstrate evidence for superlinear light emission.

Flake like V{sub 2}O{sub 5} nanoparticles for ethanol sensing at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chitra, M.; Uthayarani, K.; Rajasekaran, N.

2016-05-23

The versatile redox property of vanadium oxide explores it in various applications like catalysis, electrochromism, electrochemistry, energy storage, sensors, microelectronics, batteries etc., In this present work, vanadium oxide was prepared via hydrothermal route followed by calcination. The structural and lattice parameters were analysed from the powder X-ray diffraction (XRD) pattern. The morphology and the composition of the sample were obtained from Field emission Scanning electron microscopic (FeSEM) and Energy Dispersive X-ray (EDAX) Spectrometric analysis respectively. The sensitivity, response – recovery time of the sample towards ethanol (0 ppm – 300 ppm) sensing at room temperature was measured and the present investigation onmore » vanadium oxide nanoparticles over the flakes shows better sensitivity (30%) at room temperature.« less

The effects of elevated temperatures on the structural properties of fiber composite materials suitable for use in space shuttle and other space vehicles

NASA Technical Reports Server (NTRS)

Wright, M. A.

1972-01-01

The effects of high temperatures on the structural properties of fiber composite materials for use in spacecraft structures are investigated. Various mechanical properties of boron reinforced aluminum alloys were measured. It was observed that cycling these materials through temperatures that varied from room temperature to 425 C could seriously degrade the properties. The extent of the observed effects depended on alloy type and the maximum cyclic temperature used. Results are discussed in terms of upper and lower strength bonds calculated from the strengths of individual fibers.

Fabrication and evaluation of cold/formed/weldbrazed beta-titanium skin-stiffened compression panels

NASA Technical Reports Server (NTRS)

Royster, D. M.; Bales, T. T.; Davis, R. C.; Wiant, H. R.

1983-01-01

The room temperature and elevated temperature buckling behavior of cold formed beta titanium hat shaped stiffeners joined by weld brazing to alpha-beta titanium skins was determined. A preliminary set of single stiffener compression panels were used to develop a data base for material and panel properties. These panels were tested at room temperature and 316 C (600 F). A final set of multistiffener compression panels were fabricated for room temperature tests by the process developed in making the single stiffener panels. The overall geometrical dimensions for the multistiffener panels were determined by the structural sizing computer code PASCO. The data presented from the panel tests include load shortening curves, local buckling strengths, and failure loads. Experimental buckling loads are compared with the buckling loads predicted by the PASCO code. Material property data obtained from tests of ASTM standard dogbone specimens are also presented.

Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001) Alloys

PubMed Central

Lungu, George A.; Apostol, Nicoleta G.; Stoflea, Laura E.; Costescu, Ruxandra M.; Popescu, Dana G.; Teodorescu, Cristian M.

2013-01-01

Ferromagnetic FexGe1−x with x = 2%–9% are obtained by Fe deposition onto Ge(001) at high temperatures (500 °C). Low energy electron diffraction (LEED) investigation evidenced the preservation of the (1 × 1) surface structure of Ge(001) with Fe deposition. X-ray photoelectron spectroscopy (XPS) at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe3 to approximately FeGe2, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE) evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane [110] easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics. PMID:28809330

Magnetostructural phase transformations in Tb 1-x Mn 2

DOE PAGES

Zou, Junding; Paudyal, Durga; Liu, Jing; ...

2015-01-16

Magnetism and phase transformations in non-stoichiometric Tb 1-xMn 2 (x = 0.056, 0.039) have been studied as functions of temperature and magnetic field using magnetization, heat capacity, and X-ray powder diffraction measurements. Lowering the temperature, the compounds sequentially order ferrimagnetically and antiferromagnetically, and finally, exhibit spin reorientation transitions. Moreover, these structural distortions from room temperature cubic to low temperature rhombohedral structures occur at T N, and are accompanied by large volume changes reaching ~-1.27% and -1.42%, respectively. First principles electronic structure calculations confirm the phase transformation from the ferrimagnetic cubic structure to the antiferromagnetic rhombohedral structure in TbMn 2.

Giant room-temperature electrostrictive coefficients in lead-free relaxor ferroelectric ceramics by compositional tuning

NASA Astrophysics Data System (ADS)

Ullah, Aman; Gul, Hafiza Bushra; Ullah, Amir; Sheeraz, Muhammad; Bae, Jong-Seong; Jo, Wook; Ahn, Chang Won; Kim, Ill Won; Kim, Tae Heon

2018-01-01

A thermotropic phase boundary between non-ergodic and ergodic relaxor phases is tuned in lead-free Bi1/2Na1/2TiO3-based ceramics through a structural transition driven by compositional modification (usually named as "morphotropic approach"). The substitution of Bi(Ni1/2Ti1/2)O3 for Bi1/2(Na0.78K0.22)1/2TiO3 induces a transition from tetragonal to "metrically" cubic phase and thereby, the ergodic relaxor ferroelectric phase becomes predominant at room temperature. A shift of the transition temperature (denoted as TF-R) in the non-ergodic-to-ergodic phase transition is corroborated via temperature-dependent dielectric permittivity and loss measurements. By monitoring the chemical composition dependence of polarization-electric field and strain-electric field hysteresis loops, it is possible to track the critical concentration of Bi(Ni1/2Ti1/2)O3 where the (1 - x)Bi0.5(Na0.78K0.22)0.5TiO3-xBi(Ni0.5Ti0.5)O3 ceramic undergoes the phase transition around room temperature. At the Bi(Ni0.5Ti0.5)O3 content of x = 0.050, the highest room-temperature electrostrictive coefficient of 0.030 m4/C2 is achieved with no hysteretic characteristic, which can foster the realization of actual electrostrictive devices with high operational efficiency at room temperature.

Thermal Improvement and Stability of Si3N4/GeNx/p- and n-Ge Structures Prepared by Electron-Cyclotron-Resonance Plasma Nitridation and Sputtering at Room Temperature

NASA Astrophysics Data System (ADS)

Fukuda, Yukio; Okamoto, Hiroshi; Iwasaki, Takuro; Izumi, Kohei; Otani, Yohei; Ishizaki, Hiroki; Ono, Toshiro

2012-09-01

This paper reports on the thermal improvement of Si3N4/GeNx/Ge structures. After the Si3N4 (5 nm)/GeNx (2 nm) stacks were prepared on Ge substrates by electron-cyclotron-resonance plasma nitridation and sputtering at room temperature, they were thermally annealed in atmospheric N2 + 10% H2 ambient at temperatures from 400 to 600 °C. It was demonstrated that the electronic properties of the GeNx/Ge interfaces were thermally improved at temperatures of up to 500 °C with a minimum interface trap density (Dit) of ˜1×1011 cm-2 eV-1 near the Ge midgap, whereas the interface properties were slightly degraded after annealing at 600 °C with a minimum Dit value of ˜4×1011 cm-2 eV-1.

Structural and Magnetic Properties of Sputter-Deposited Polycrystalline Ni-Mn-Ga Ferromagnetic Shape-Memory Thin Films

NASA Astrophysics Data System (ADS)

Vinodh Kumar, S.; Seenithurai, S.; Manivel Raja, M.; Mahendran, M.

2015-10-01

Polycrystalline Ni-Mn-Ga ferromagnetic shape-memory thin films have been deposited on Si (100) substrates using a direct-current magnetron sputtering technique. The microstructure and the temperature dependence of magnetic properties of the films have been investigated by x-ray diffraction, scanning electron microscopy, and thermomagnetic measurements. As-deposited Ni50.2Mn30.6Ga19.2 film showed quasi-amorphous structure with paramagnetic nature at room temperature. When annealed at 873 K, the quasi-amorphous film attained crystallinity and possessed L21 cubic ordering with high magnetic transition temperature. Saturation magnetization and coercivity values for the annealed film were found to be 220 emu/cm3 and 70 Oe, respectively, indicating soft ferromagnetic character with low magnetocrystalline anisotropy. The magnetic transitions of the film deposited at 100 W were above room temperature, making this a potential candidate for use in microelectromechanical system devices.

Room temperature structural and dielectric studies of Pb(Fe0.585Nb0.25W0.165)O3 solid solution

NASA Astrophysics Data System (ADS)

Nagaraja, T.; Dadami, Sunanda T.; Angadi, Basavaraj

2018-05-01

The perovskite A(B'B''B''')O3 structure Pb(Fe0.585Nb0.25W0.165)O3 (PFNW) multiferroic material was synthesized by single step solid state reaction method. The single phase was achieved at low temperature with optimized synthesis parameters as calcination (700°C/2hr) and sintering (800 °C /3hr). Single phase was confirmed by room temperature (RT) X-ray diffraction (XRD). The scanning electron microscopy (SEM) shows the uniform distribution of grains throughout the surface of PFNW and the energy dispersive X-ray spectroscopy (EDX) confirms the exact elemental composition as that of the experimental. Fourier transform infrared spectroscopy (FTIR) exhibits two absorption bands at 602 cm-1 and 1385 cm-1 corresponds to the bending and stretching vibrations of metal oxides. RT dielectric studies (dielectric constant, tanδ, AC conductivity) exhibits maximum values at lower frequency region and decreases as the frequency increases. Thesingle semicircular arc in RT impedance spectra (Nyquist plot)indicatesthe contribution to the conductivity is from grains only. Hence PFNW is a potential candidate for near room temperature applications.

A superhard, quenchable carbon polymorph formed by the room-temperature compression of graphite (Invited)

NASA Astrophysics Data System (ADS)

Wang, Y.; Kiefer, B.; Lee, K. K.

2010-12-01

As one of the revolutionary inventions of the 20th century, synthetic diamond has had a large impact on industry and on scientific research. However, the necessities of high pressures, high temperatures and a metal catalyst during the manufacturing of synthetic diamond make it energy consuming thus limits its availability and use. Here, we report on the synthesis of a superhard non-diamond material resulting from the compression of graphite above ~20 GPa at room temperature without the utilization of metal catalysts. The final product includes a nano-sized phase of carbon that is recoverable at ambient conditions. Furthermore, the ring cracks left on the diamond anvils suggest that the hardness of this post-graphite phase is at least comparable to that of diamond. We use high-resolution synchrotron x-ray diffraction and micro-Raman spectroscopy to monitor the structural transformation in graphite under high pressure and room temperature and find the transition to be sluggish. The possible crystal structure of the new, quenchable phase will be discussed and the time-dependent formation of this superhard post-graphite carbon will be addressed and compared to first-principle predictions.

Room-temperature spin-orbit torque in NiMnSb

NASA Astrophysics Data System (ADS)

Ciccarelli, C.; Anderson, L.; Tshitoyan, V.; Ferguson, A. J.; Gerhard, F.; Gould, C.; Molenkamp, L. W.; Gayles, J.; Železný, J.; Šmejkal, L.; Yuan, Z.; Sinova, J.; Freimuth, F.; Jungwirth, T.

2016-09-01

Materials that crystallize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneously, inversion asymmetries in their crystal structure and relativistic spin-orbit coupling led to discoveries of non-equilibrium spin-polarization phenomena that are now extensively explored as an electrical means for manipulating magnetic moments in a variety of spintronic structures. Current research of these relativistic spin-orbit torques focuses primarily on magnetic transition-metal multilayers. The low-temperature diluted magnetic semiconductor (Ga, Mn)As, in which spin-orbit torques were initially discovered, has so far remained the only example showing the phenomenon among bulk non-centrosymmetric ferromagnets. Here we present a general framework, based on the complete set of crystallographic point groups, for identifying the potential presence and symmetry of spin-orbit torques in non-centrosymmetric crystals. Among the candidate room-temperature ferromagnets we chose to use NiMnSb, which is a member of the broad family of magnetic Heusler compounds. By performing all-electrical ferromagnetic resonance measurements in single-crystal epilayers of NiMnSb we detect room-temperature spin-orbit torques generated by effective fields of the expected symmetry and of a magnitude consistent with our ab initio calculations.

Conformational variation of proteins at room temperature is not dominated by radiation damage

DOE PAGES

Russi, Silvia; González, Ana; Kenner, Lillian R.; ...

2017-01-01

Protein crystallography data collection at synchrotrons is routinely carried out at cryogenic temperatures to mitigate radiation damage. Although damage still takes place at 100 K and below, the immobilization of free radicals increases the lifetime of the crystals by approximately 100-fold. Recent studies have shown that flash-cooling decreases the heterogeneity of the conformational ensemble and can hide important functional mechanisms from observation. These discoveries have motivated increasing numbers of experiments to be carried out at room temperature. However, the trade-offs between increased risk of radiation damage and increased observation of alternative conformations at room temperature relative to cryogenic temperature havemore » not been examined. A considerable amount of effort has previously been spent studying radiation damage at cryo-temperatures, but the relevance of these studies to room temperature diffraction is not well understood. Here, the effects of radiation damage on the conformational landscapes of three different proteins ( T. danielli thaumatin, hen egg-white lysozyme and human cyclophilin A) at room (278 K) and cryogenic (100 K) temperatures are investigated. Increasingly damaged datasets were collected at each temperature, up to a maximum dose of the order of 10 7 Gy at 100 K and 10 5 Gy at 278 K. Although it was not possible to discern a clear trend between damage and multiple conformations at either temperature, it was observed that disorder, monitored by B-factor-dependent crystallographic order parameters, increased with higher absorbed dose for the three proteins at 100 K. At 278 K, however, the total increase in this disorder was only statistically significant for thaumatin. A correlation between specific radiation damage affecting side chains and the amount of disorder was not observed. Lastly, this analysis suggests that elevated conformational heterogeneity in crystal structures at room temperature is observed despite radiation damage, and not as a result thereof.« less

Conformational variation of proteins at room temperature is not dominated by radiation damage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Russi, Silvia; González, Ana; Kenner, Lillian R.

Protein crystallography data collection at synchrotrons is routinely carried out at cryogenic temperatures to mitigate radiation damage. Although damage still takes place at 100 K and below, the immobilization of free radicals increases the lifetime of the crystals by approximately 100-fold. Recent studies have shown that flash-cooling decreases the heterogeneity of the conformational ensemble and can hide important functional mechanisms from observation. These discoveries have motivated increasing numbers of experiments to be carried out at room temperature. However, the trade-offs between increased risk of radiation damage and increased observation of alternative conformations at room temperature relative to cryogenic temperature havemore » not been examined. A considerable amount of effort has previously been spent studying radiation damage at cryo-temperatures, but the relevance of these studies to room temperature diffraction is not well understood. Here, the effects of radiation damage on the conformational landscapes of three different proteins ( T. danielli thaumatin, hen egg-white lysozyme and human cyclophilin A) at room (278 K) and cryogenic (100 K) temperatures are investigated. Increasingly damaged datasets were collected at each temperature, up to a maximum dose of the order of 10 7 Gy at 100 K and 10 5 Gy at 278 K. Although it was not possible to discern a clear trend between damage and multiple conformations at either temperature, it was observed that disorder, monitored by B-factor-dependent crystallographic order parameters, increased with higher absorbed dose for the three proteins at 100 K. At 278 K, however, the total increase in this disorder was only statistically significant for thaumatin. A correlation between specific radiation damage affecting side chains and the amount of disorder was not observed. Lastly, this analysis suggests that elevated conformational heterogeneity in crystal structures at room temperature is observed despite radiation damage, and not as a result thereof.« less

Nanoindentation hardness and atomic force microscope imaging studies of pressure-quenched zirconium metal

NASA Astrophysics Data System (ADS)

Catledge, Shane A.; Spencer, Philemon T.; Vohra, Yogesh K.

2000-11-01

We have carried out mechanical property measurements on zirconium metal compressed in a diamond anvil cell to 19 GPa at room temperature with subsequent quenching to room pressure. The irreversible transformation from the ambient hexagonal-close-packed phase to the simple hexagonal ω phase (AlB2 structure) is confirmed by synchrotron energy dispersive x-ray diffraction followed by nanoindentation of the pressure-quenched sample. We document an 80% increase in hardness as a consequence of the pressure-induced transformation to the ω phase at room temperature. This is a large increase for a metallic phase transformation and can be attributed to the presence of sp2-hybrid bonds forming graphite-like nets in the (0001) plane of the AlB2 structure. Atomic force microscopy of the indents shows that a plastic deformation of 2 μm in depth was achieved with a force of 200 mN.

Serial Femtosecond Crystallography of G Protein-Coupled Receptors

PubMed Central

Liu, Wei; Wacker, Daniel; Gati, Cornelius; Han, Gye Won; James, Daniel; Wang, Dingjie; Nelson, Garrett; Weierstall, Uwe; Katritch, Vsevolod; Barty, Anton; Zatsepin, Nadia A.; Li, Dianfan; Messerschmidt, Marc; Boutet, Sébastien; Williams, Garth J.; Koglin, Jason E.; Seibert, M. Marvin; Wang, Chong; Shah, Syed T.A.; Basu, Shibom; Fromme, Raimund; Kupitz, Christopher; Rendek, Kimberley N.; Grotjohann, Ingo; Fromme, Petra; Kirian, Richard A.; Beyerlein, Kenneth R.; White, Thomas A.; Chapman, Henry N.; Caffrey, Martin; Spence, John C.H.; Stevens, Raymond C.; Cherezov, Vadim

2014-01-01

X-ray crystallography of G protein-coupled receptors and other membrane proteins is hampered by difficulties associated with growing sufficiently large crystals that withstand radiation damage and yield high-resolution data at synchrotron sources. Here we used an x-ray free-electron laser (XFEL) with individual 50-fs duration x-ray pulses to minimize radiation damage and obtained a high-resolution room temperature structure of a human serotonin receptor using sub-10 µm microcrystals grown in a membrane mimetic matrix known as lipidic cubic phase. Compared to the structure solved by traditional microcrystallography from cryo-cooled crystals of about two orders of magnitude larger volume, the room temperature XFEL structure displays a distinct distribution of thermal motions and conformations of residues that likely more accurately represent the receptor structure and dynamics in a cellular environment. PMID:24357322

Study of the structural and optical properties of GaP(N) layers synthesized by molecular-beam epitaxy on Si(100) 4° substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kryzhanovskaya, N. V., E-mail: NataliaKryzh@gmail.com; Polubavkina, Yu. S.; Nevedomskiy, V. N.

The structural and optical properties of GaP and GaPN layers synthesized by molecular-beam epitaxy on Si(100) substrates misoriented by 4° are studied. The possibility of producing GaP buffer layers that exhibit a high degree of heterointerface planarity and an outcropping dislocation density of no higher than ~2 × 10{sup 8} cm{sup –2} is shown. Emission from the Si/GaP/GaPN structure in the spectral range of 630–640 nm at room temperature is observed. Annealing during growth of the Si/GaP/GaPN structure makes it possible to enhance the room-temperature photoluminescence intensity by a factor of 2.6, with no shift of the maximum of themore » emission line.« less

Non-ionic block copolymers leading to a highly ordered organosilica material

NASA Astrophysics Data System (ADS)

Rebbin, V.; Rothkirch, A.; Vainio, U.; Funari, S. S.

2012-03-01

Phenylene-bridged periodic mesoporous organosilica (PMO) materials with hexaethylene glycol mono hexadecylether (C16(EO)6) as structure directing agent (SDA) in acidic solution were synthesised and the reaction was studied in different conditions, including in situ small angle X-ray scattering at room temperature and at 60 °C. The in situ SAXS investigations at 60 °C show the formation of a 2D hexagonal mesostructure after 3 hours reaction time. In contrast to these results the same reaction performed in the laboratory produced a powder that, after drying at room temperature, shows a large number of diffraction peaks, allowing identifying a lamellar structure, possibly in coexistence of a micellar cubic structure (space group Pm3n). Aposteriori removal of the surfactant from the powder synthesised in the laboratory led to the collapse of the lamellar structure.

A study of photomodulated reflectance on staircase-like, n-doped GaAs/AlxGa1−xAs quantum well structures

PubMed Central

2012-01-01

In this study, photomodulated reflectance (PR) technique was employed on two different quantum well infrared photodetector (QWIP) structures, which consist of n-doped GaAs quantum wells (QWs) between undoped AlxGa1−xAs barriers with three different x compositions. Therefore, the barrier profile is in the form of a staircase-like barrier. The main difference between the two structures is the doping profile and the doping concentration of the QWs. PR spectra were taken at room temperature using a He-Ne laser as a modulation source and a broadband tungsten halogen lamp as a probe light. The PR spectra were analyzed using Aspnes’ third derivative functional form. Since the barriers are staircase-like, the structure has different ground state energies; therefore, several optical transitions take place in the spectrum which cannot be resolved in a conventional photoluminescence technique at room temperature. To analyze the experimental results, all energy levels in the conduction and in the valance band were calculated using transfer matrix technique, taking into account the effective mass and the parabolic band approximations. A comparison of the PR results with the calculated optical transition energies showed an excellent agreement. Several optical transition energies of the QWIP structures were resolved from PR measurements. It is concluded that PR spectroscopy is a very useful experimental tool to characterize complicated structures with a high accuracy at room temperature. PMID:23146126

A study of photomodulated reflectance on staircase-like, n-doped GaAs/AlxGa1-xAs quantum well structures.

PubMed

Donmez, Omer; Nutku, Ferhat; Erol, Ayse; Arikan, Cetin M; Ergun, Yuksel

2012-11-12

In this study, photomodulated reflectance (PR) technique was employed on two different quantum well infrared photodetector (QWIP) structures, which consist of n-doped GaAs quantum wells (QWs) between undoped AlxGa1-xAs barriers with three different x compositions. Therefore, the barrier profile is in the form of a staircase-like barrier. The main difference between the two structures is the doping profile and the doping concentration of the QWs. PR spectra were taken at room temperature using a He-Ne laser as a modulation source and a broadband tungsten halogen lamp as a probe light. The PR spectra were analyzed using Aspnes' third derivative functional form.Since the barriers are staircase-like, the structure has different ground state energies; therefore, several optical transitions take place in the spectrum which cannot be resolved in a conventional photoluminescence technique at room temperature. To analyze the experimental results, all energy levels in the conduction and in the valance band were calculated using transfer matrix technique, taking into account the effective mass and the parabolic band approximations. A comparison of the PR results with the calculated optical transition energies showed an excellent agreement. Several optical transition energies of the QWIP structures were resolved from PR measurements. It is concluded that PR spectroscopy is a very useful experimental tool to characterize complicated structures with a high accuracy at room temperature.

A study of photomodulated reflectance on staircase-like, n-doped GaAs/Al x Ga1- x As quantum well structures

NASA Astrophysics Data System (ADS)

Donmez, Omer; Nutku, Ferhat; Erol, Ayse; Arikan, Cetin M.; Ergun, Yuksel

2012-11-01

In this study, photomodulated reflectance (PR) technique was employed on two different quantum well infrared photodetector (QWIP) structures, which consist of n-doped GaAs quantum wells (QWs) between undoped Al x Ga1- x As barriers with three different x compositions. Therefore, the barrier profile is in the form of a staircase-like barrier. The main difference between the two structures is the doping profile and the doping concentration of the QWs. PR spectra were taken at room temperature using a He-Ne laser as a modulation source and a broadband tungsten halogen lamp as a probe light. The PR spectra were analyzed using Aspnes' third derivative functional form. Since the barriers are staircase-like, the structure has different ground state energies; therefore, several optical transitions take place in the spectrum which cannot be resolved in a conventional photoluminescence technique at room temperature. To analyze the experimental results, all energy levels in the conduction and in the valance band were calculated using transfer matrix technique, taking into account the effective mass and the parabolic band approximations. A comparison of the PR results with the calculated optical transition energies showed an excellent agreement. Several optical transition energies of the QWIP structures were resolved from PR measurements. It is concluded that PR spectroscopy is a very useful experimental tool to characterize complicated structures with a high accuracy at room temperature.

Delayed elasticity in Zerodur® at room temperature

NASA Astrophysics Data System (ADS)

Pepi, John W.; Golini, Donald

1991-12-01

Much has been written about structural relaxation, viscous flow, delayed elasticity, hysteresis, and other dimensional stability phenomena of glass and ceramics at elevated temperatures. Less has been documented about similar effects at room temperature. The time dependent phenomenon of delayed elasticity exhibited by Zerodur has been studied at room temperature and is presented here. Using a high-performance mechanical profilometer, a delayed strain on the order of 1 percent is realized over a period of a few weeks, under low stress levels. An independent test using optical interferometry validates the results. A comparison of Corning ULE silica glass is also made. The effect is believed to be related to the alkali oxide content of the glass ceramic and rearrangement of the ion groups within the structure during stress. The effect, apparent under externally applied load, is elastic and repeatable, that is, no hysteresis of permanent set, as measured at elevated temperature, is evidenced within measurement capabilities. Nonetheless, it must be accounted for in determining the magnitude of distortion under load (delayed elastic creep) and upon load removal (delayed elastic recovery). This is particularly important for large lightweight optics which might undergo large strain during fabrication and environmental loading, such as experienced in gravity release or in dynamic control of active optics.

Direct observation of the magnetic domain evolution stimulated by temperature and magnetic field in PrMnGeSi alloy

NASA Astrophysics Data System (ADS)

Zuo, S. L.; Zhang, B.; Qiao, K. M.; Peng, L. C.; Li, R.; Xiong, J. F.; Zhang, Y.; Zhao, X.; Liu, D.; Zhao, T. Y.; Sun, J. R.; Hu, F. X.; Zhang, Y.; Shen, B. G.

2018-05-01

The magnetic domain evolution behavior under external field stimuli of temperature and magnetic field in PrMn2Ge0.4Si1.6 compound is investigated using Lorentz transmission electron microscopy. A spontaneous 180° magnetic domain is observed at room temperature and it changes with temperature. Dynamic magnetization process is related to the rotation of magnetic moments, resulting in the transforming of magnetic domains from 180° type to a uniform ferromagnetic state with almost no pinning effects under the in-plane magnetic field at room temperature. X-ray powder diffraction is performed on PrMn2Ge0.4Si1.6 at different temperatures to study the temperature dependence of crystal structure and lattice parameter.

Room temperature, very sensitive thermometer using a doubly clamped microelectromechanical beam resonator for bolometer applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Y., E-mail: zhangya@iis.u-tokyo.ac.jp; Watanabe, Y.; Hosono, S.

We propose a room temperature, all electrical driving and detecting, very sensitive thermometer structure using a microelectromechanical (MEMS) resonator for bolometer applications. We have fabricated a GaAs doubly clamped MEMS beam resonator whose oscillation can be excited and detected by the piezoelectric effect. When a heating power is applied to a NiCr film deposited on the MEMS beam surface, internal thermal stress is generated in the beam, leading to a reduction in the resonance frequency. The present device detects the shift in the resonance frequency caused by heating and works as a very sensitive thermometer. When the resonator was drivenmore » by a voltage slightly below the threshold for the nonlinear, hysteretic oscillation, the thermometer showed a voltage responsivity of about 3300 V/W, while keeping a low noise spectral density of about 60 nV/Hz{sup 1/2}, demonstrating a noise equivalent power of <20 pW/Hz{sup 1/2} even at room temperature. The observed effect can be used for realizing high-sensitivity terahertz bolometers for room-temperature operation.« less

Relationships Between Molecular Structure and Chemical Reactivity in Hypergolic Ionic Liquids: Progress Toward Designing Green Fuels for Bipropellant Applications

DTIC Science & Technology

2012-05-01

molten salts can be employed over a wide range of applications, which include solvents, 7 electrolytes , 8 pharmaceuticals and therapeutics,9 and...waxy, hygroscopic solid at room temperature, where the additional products in the HP series exist as liquids at room 9 temperature. In general...compressed aluminum pans. Melting and decomposition points for solids were measured by DSC from 40 to 400 oC at a scan rate of 5 ºC/min. IR spectra

A Novel and Non-Cytotoxic Self-Healing Supramolecular Elastomer Synthesized with Small Molecular Biological Acids.

PubMed

Liu, Ling; Pan, Cheng; Zhang, Liqun; Guo, Baochun

2016-10-01

A novel and non-cytotoxic self-healing supramolecular elastomer (SE) is synthesized with small-molecular biological acids by hydrogen-bonding interactions. The synthesized SEs behave as rubber at room temperature without additional plasticizers or crosslinkers, which is attributed to the phase-separated structure. The SE material exhibits outstanding self-healing capability at room temperature and essential non-cytotoxicity, which makes it a potential candidate for biomedical applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In situ straining investigation of slip transfer across α2 lamellae at room temperature in a lamellar TiAl alloy

NASA Astrophysics Data System (ADS)

Singh, J. B.; Molénat, G.; Sundararaman, M.; Banerjee, S.; Saada, G.; Veyssière, P.; Couret, A.

2006-01-01

Processes by which deformation spreads throughout a lamellar TiAl alloy have been investigated by in situ tensile experiments performed at room temperature in a transmission electron microscope. Several situations are found and analysed in which dislocations cross the ?/a2 interfaces and the a2 lamellae - the hard phase of the structure. Conditions by which strain transfer can be elastically mediated across sufficiently thin a2 lamellae are discussed.

Red phosphorescence from benzo[2,1,3]thiadiazoles at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gutierrez, Gregory D.; Sazama, Graham T.; Wu, Tony

2016-05-23

In this paper, we describe the red phosphorescence exhibited by a class of structurally simple benzo[2,1,3]thiadiazoles at room temperature. The photophysical properties of these molecules in deoxygenated cyclohexane, including their absorption spectra, steady-state photoluminescence and excitation spectra, and phosphorescence lifetimes, are presented. Finally, time-dependent density functional theory calculations were carried out to better understand the electronic excited states of these benzo[2,1,3]thiadiazoles and why they are capable of phosphorescence.

Highly strained InxGa(1-x)As-InyAl(1-y)As (x>0.8,y<0.3) layers for short wavelength QWIP and QCL structures grown by MBE

NASA Astrophysics Data System (ADS)

Missous, M.; Mitchell, C.; Sly, J.; Lai, K. T.; Gupta, R.; Haywood, S. K.

2004-01-01

Highly strained quantum cascade laser (QCL) and quantum well infrared photodetector (QWIPs) structures based on InxGa(1-x)As-InyAl(1-y)As (x>0.8,y<0.3) layers have been grown by molecular beam epitaxy. Conditions of exact stoichiometric growth were used at a temperature of ∼420°C to produce structures that are suitable for both emission and detection in the 2- 5 μm mid-infrared regime. High structural integrity, as assessed by double crystal X-ray diffraction, room temperature photoluminescence and electrical characteristics were observed. Strong room temperature intersubband absorption in highly tensile strained and strain-compensated In 0.84Ga 0.16As/AlAs/In 0.52Al 0.48As double barrier quantum wells grown on InP substrates is demonstrated. Γ- Γ intersubband transitions have been observed across a wide range of the mid-infrared spectrum (2- 7 μm) in three structures of differing In 0.84Ga 0.16As well width (30, 45, and 80 Å). We demonstrate short-wavelength IR, intersubband operation in both detection and emission for application in QC and QWIP structures. By pushing the InGaAs-InAlAs system to its ultimate limit, we have obtained the highest band offsets that are theoretically possible in this system both for the Γ- Γ bands and the Γ-X bands, thereby opening up the way for both high power and high efficiency coupled with short-wavelength operation at room temperature. The versatility of this material system and technique in covering a wide range of the infrared spectrum is thus demonstrated.

Electro-caloric effect in lead-free Sn doped BaTiO{sub 3} ceramics at room temperature and low applied fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Upadhyay, Sanjay Kumar; Reddy, V. Raghavendra, E-mail: varimalla@yahoo.com, E-mail: vrreddy@csr.res.in; Bag, Pallab

2014-09-15

Structural, dielectric, ferroelectric (FE), {sup 119}Sn Mössbauer, and specific heat measurements of polycrystalline BaTi{sub 1–x}Sn{sub x}O{sub 3} (x = 0% to 15%) ceramics are reported. Phase purity and homogeneous phase formation with Sn doping is confirmed from x-ray diffraction and {sup 119}Sn Mössbauer measurements. With Sn doping, the microstructure is found to change significantly. Better ferroelectric properties at room temperature, i.e., increased remnant polarization (38% more) and very low field switchability (225% less) are observed for x = 5% sample as compared to other samples and the results are explained in terms of grain size effects. With Sn doping, merging of all the phasemore » transitions into a single one is observed for x ≥ 10% and for x = 5%, the tetragonal to orthorhombic transition temperature is found close to room temperature. As a consequence better electro-caloric effects are observed for x = 5% sample and therefore is expected to satisfy the requirements for non-toxic, low energy (field) and room temperature based applications.« less

Low- and room-temperature X-ray structures of protein kinase A ternary complexes shed new light on its activity.

PubMed

Kovalevsky, Andrey Y; Johnson, Hanna; Hanson, B Leif; Waltman, Mary Jo; Fisher, S Zoe; Taylor, Susan; Langan, Paul

2012-07-01

Post-translational protein phosphorylation by protein kinase A (PKA) is a ubiquitous signalling mechanism which regulates many cellular processes. A low-temperature X-ray structure of the ternary complex of the PKA catalytic subunit (PKAc) with ATP and a 20-residue peptidic inhibitor (IP20) at the physiological Mg(2+) concentration of ∼0.5 mM (LT PKA-MgATP-IP20) revealed a single metal ion in the active site. The lack of a second metal in LT PKA-MgATP-IP20 renders the β- and γ-phosphoryl groups of ATP very flexible, with high thermal B factors. Thus, the second metal is crucial for tight positioning of the terminal phosphoryl group for transfer to a substrate, as demonstrated by comparison of the former structure with that of the LT PKA-Mg(2)ATP-IP20 complex obtained at high Mg(2+) concentration. In addition to its kinase activity, PKAc is also able to slowly catalyze the hydrolysis of ATP using a water molecule as a substrate. It was found that ATP can be readily and completely hydrolyzed to ADP and a free phosphate ion in the crystals of the ternary complex PKA-Mg(2)ATP-IP20 by X-ray irradiation at room temperature. The cleavage of ATP may be aided by X-ray-generated free hydroxyl radicals, a very reactive chemical species, which move rapidly through the crystal at room temperature. The phosphate anion is clearly visible in the electron-density maps; it remains in the active site but slides about 2 Å from its position in ATP towards Ala21 of IP20, which mimics the phosphorylation site. The phosphate thus pushes the peptidic inhibitor away from the product ADP, while resulting in dramatic conformational changes of the terminal residues 24 and 25 of IP20. X-ray structures of PKAc in complex with the nonhydrolysable ATP analogue AMP-PNP at both room and low temperature demonstrated no temperature effects on the conformation and position of IP20.

Energy-filtered cold electron transport at room temperature.

PubMed

Bhadrachalam, Pradeep; Subramanian, Ramkumar; Ray, Vishva; Ma, Liang-Chieh; Wang, Weichao; Kim, Jiyoung; Cho, Kyeongjae; Koh, Seong Jin

2014-09-10

Fermi-Dirac electron thermal excitation is an intrinsic phenomenon that limits functionality of various electron systems. Efforts to manipulate electron thermal excitation have been successful when the entire system is cooled to cryogenic temperatures, typically <1 K. Here we show that electron thermal excitation can be effectively suppressed at room temperature, and energy-suppressed electrons, whose energy distribution corresponds to an effective electron temperature of ~45 K, can be transported throughout device components without external cooling. This is accomplished using a discrete level of a quantum well, which filters out thermally excited electrons and permits only energy-suppressed electrons to participate in electron transport. The quantum well (~2 nm of Cr2O3) is formed between source (Cr) and tunnelling barrier (SiO2) in a double-barrier-tunnelling-junction structure having a quantum dot as the central island. Cold electron transport is detected from extremely narrow differential conductance peaks in electron tunnelling through CdSe quantum dots, with full widths at half maximum of only ~15 mV at room temperature.

Tungsten-reinforced tantalum

NASA Technical Reports Server (NTRS)

Bacigalupi, R. J.; Breitwieser, R.

1972-01-01

Method is described for producing tungsten-reinforced tantalum, a material possessing the high temperature strength of tungsten and room temperature ductility and weldability of tantalum. This material is produced by bonding together and overlaying structure of tungsten wires with chemical vapor deposited tantalum.

A highly sensitive room temperature H2S gas sensor based on SnO2 multi-tube arrays bio-templated from insect bristles.

PubMed

Tian, Junlong; Pan, Feng; Xue, Ruiyang; Zhang, Wang; Fang, Xiaotian; Liu, Qinglei; Wang, Yuhua; Zhang, Zhijian; Zhang, Di

2015-05-07

A tin oxide multi-tube array (SMTA) with a parallel effect was fabricated through a simple and promising method combining chemosynthesis and biomimetic techniques; a biomimetic template was derived from the bristles on the wings of the Alpine Black Swallowtail butterfly (Papilio maackii). SnO2 tubes are hollow and porous structures with micro-pores regularly distributed on the wall. The morphology, the delicate microstructure and the crystal structure of this SMTA were characterized by super resolution digital microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The SMTA exhibits a high sensitivity to H2S gas at room temperature. It also exhibits a short response/recovery time, with an average value of 14/30 s at 5 ppm. In particular, heating is not required for the SMTA in the gas sensitivity measurement process. On the basis of these results, SMTA is proposed as a suitable new material for the design and fabrication of room-temperature H2S gas sensors.

Self-Assembled Layered Supercell Structure of Bi2AlMnO6 with Strong Room-Temperature Multiferroic Properties.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Leigang; Boullay, Philippe; Lu, Ping

2017-02-01

Room-temperature (RT) multiferroics, possessing ferroelectricity and ferromagnetism simultaneously at RT, hold great promise in miniaturized devices including sensors, actuators, transducers, and multi-state memories. In this work, we report a novel 2D layered RT multiferroic system with self-assembled layered supercell structure consisting of two mismatch-layered sub-lattices of [Bi 3O 3+δ] and [MO 2] 1.84 (M=Al/Mn, simply named as BAMO), i.e., alternative layered stacking of two mutually incommensurate sublattices made of a three-layer-thick Bi-O slab and a one-layer-thick Al/Mn-O octahedra slab along the out-of-plane direction. Strong room-temperature multiferroic responses, e.g., ferromagnetic and ferroelectric properties, have been demonstrated and attributed to the highlymore » anisotropic 2D nature of the non-ferromagnetic and ferromagnetic sublattices which are highly mismatched. The work demonstrates an alternative design approach for new 2D layered oxide materials that hold promises as single-phase multiferroics, 2D oxides with tunable bandgaps, and beyond.« less

Room temperature negative differential resistance in terahertz quantum cascade laser structures

DOE PAGES

Albo, Asaf; Hu, Qing; Reno, John L.

2016-08-24

The mechanisms that limit the temperature performance of GaAs/Al 0.15GaAs-based terahertz quantum cascade lasers (THz-QCLs) have been identified as thermally activated LO-phonon scattering and leakage of charge carriers into the continuum. Consequently, the combination of highly diagonal optical transition and higher barriers should significantly reduce the adverse effects of both mechanisms and lead to improved temperature performance. Here, we study the temperature performance of highly diagonal THz-QCLs with high barriers. Our analysis uncovers an additional leakage channel which is the thermal excitation of carriers into bounded higher energy levels, rather than the escape into the continuum. Based on this understanding,more » we have designed a structure with an increased intersubband spacing between the upper lasing level and excited states in a highly diagonal THz-QCL, which exhibits negative differential resistance even at room temperature. Furthermore, this result is a strong evidence for the effective suppression of the aforementioned leakage channel.« less

Synthesis, structure, optical, photoluminescence and magnetic properties of K2[Co(C2O4)2(H2O)2]·4H2O

NASA Astrophysics Data System (ADS)

Narsimhulu, M.; Hussain, K. A.

2018-06-01

The synthesis, crystal structure, optical, photoluminescence and magnetic behaviour of potassium bis(oxalato)cobaltate(II)tertrahydrate{K2[Co(C2O4)2(H2O)2]·4H2O} are described. The compound was grown at room temperature from mixture of aqueous solutions by slow evaporation method. The X-ray crystallographic data showed that the compound belongs to the monoclinic crystal system with P21/n space group and Z = 4. The UV-visible diffuse absorbance spectra exhibited bands at 253, 285 and 541 nm in the visible and ultraviolet regions. The optical band gap of the compound was estimated as 3.4 eV. At room temperature, an intense photoluminescence was observed from this material around 392 nm when it excited at 254 nm. The variable temperature dc magnetic susceptibility measurements exposed paramagnetic behaviour at high temperatures and antiferromagnetic ordering at low temperatures.

Phase dependent fracture and damage evolution of polytetrafluoroethylene (PTFE)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, E. N.; Rae, P.; Orler, E. B.

2004-01-01

Compared with other polymers, polytetrafluoroethylene (PTFE) presents several advantages for load-bearing structural components including higher strength at elevated temperatures and higher toughness at lowered temperatures. Failure sensitive applications of PTFE include surgical implants, aerospace components, and chemical barriers. Polytetrafluoroethylene is semicrystalline in nature with their linear chains forming complicated phases near room temperature and ambient pressure. The presence of three unique phases near room temperature implies that failure during standard operating conditions may be strongly dependent on the phase. This paper presents a comprehensive and systematic study of fracture and damage evolution in PTFE to elicit the effects of temperature-inducedmore » phase on fracture mechanisms. The fracture behavior of PTFE is observed to undergo transitions from brittle-fracture below 19 C to ductile-fracture with crazing and some stable crack growth to plastic flow aver 30 C. The bulk failure properties are correlated to failure mechanisms through fractography and analysis of the crystalline structure.« less

A low-temperature polymorph of m-quinquephenyl.

PubMed

Gomes, Ligia R; Howie, R Alan; Low, John Nicolson; Rodrigues, Ana S M C; Santos, Luís M N B F

2012-12-01

A low-temperature polymorph of 1,1':3',1'':3'',1''':3''',1''''-quinquephenyl (m-quinquephenyl), C(30)H(22), crystallizes in the space group P2(1)/c with two molecules in the asymmetric unit. The crystal is a three-component nonmerohedral twin. A previously reported room-temperature polymorph [Rabideau, Sygula, Dhar & Fronczek (1993). Chem. Commun. pp. 1795-1797] also crystallizes with two molecules in the asymmetric unit in the space group P-1. The unit-cell volume for the low-temperature polymorph is 4120.5 (4) Å(3), almost twice that of the room-temperature polymorph which is 2102.3 (6) Å(3). The molecules in both structures adopt a U-shaped conformation with similar geometric parameters. The structural packing is similar in both compounds, with the molecules lying in layers which stack perpendicular to the longest unit-cell axis. The molecules pack alternately in the layers and in the stacked columns. In both polymorphs, the only interactions between the molecules which can stabilize the packing are very weak C-H...π interactions.

Effect of Structural Relaxation on the In-Plane Electrical Resistance of Oxygen-Underdoped ReBaCuO (Re = Y, Ho) Single Crystals

NASA Astrophysics Data System (ADS)

Vovk, Ruslan V.; Vovk, Nikolaj R.; Dobrovolskiy, Oleksandr V.

2014-05-01

The effect of jumpwise temperature variation and room-temperature storing on the basal-plane electrical resistivity of underdoped ReBaCuO (Re = Y, Ho) single crystals is investigated. Reducing the oxygen content has been revealed to lead to the phase segregation accompanied by both, labile component diffusion and structural relaxation in the sample volume. Room-temperature storing of single crystals with different oxygen hypostoichiometries leads to a substantial widening of the rectilinear segment in in conjunction with a narrowing of the temperature range of existence of the pseudogap state. It is established that the excess conductivity obeys an exponential law in a broad temperature range, while the pseudogap's temperature dependence is described satisfactory in the framework of the BCS-BEC crossover theory. Substituting yttrium with holmium essentially effects the charge distribution and the effective interaction in CuO planes, thereby stimulating disordering processes in the oxygen subsystem. This is accompanied by a notable shift of the temperature zones corresponding to transitions of the metal-insulator type and to the regime of manifestation of the pseudogap anomaly.

Numerical Modelling of Airflow and Temperature Distribution in a Living Room with Different Heat Exchange Conditions

NASA Astrophysics Data System (ADS)

Gendelis, S.; Jakovičs, A.

2010-01-01

Numerical mathematical modelling of the indoor thermal conditions and of the energy losses for separate rooms is an important part of the analysis of the heat-exchange balance and energy efficiency in buildings. The measurements of heat transfer coefficients for bounding structures, the air-tightness tests and thermographic diagnostics done for a building allow the influence of those factors to be predicted more correctly in developed numerical models. The temperature distribution and airflows in a typical room (along with the heat losses) were calculated for different heater locations and solar radiation (modelled as a heat source) through the window, as well as various pressure differences between the openings in opposite walls. The airflow velocities and indoor temperature, including its gradient, were also analysed as parameters of thermal comfort conditions. The results obtained show that all of the listed factors have an important influence on the formation of thermal comfort conditions and on the heat balance in a room.

Precursor state of oxygen molecules on the Si(001) surface during the initial room-temperature adsorption

NASA Astrophysics Data System (ADS)

Hwang, Eunkyung; Chang, Yun Hee; Kim, Yong-Sung; Koo, Ja-Yong; Kim, Hanchul

2012-10-01

The initial adsorption of oxygen molecules on Si(001) is investigated at room temperature. The scanning tunneling microscopy images reveal a unique bright O2-induced feature. The very initial sticking coefficient of O2 below 0.04 Langmuir is measured to be ˜0.16. Upon thermal annealing at 250-600 °C, the bright O2-induced feature is destroyed, and the Si(001) surface is covered with dark depressions that seem to be oxidized structures with -Si-O-Si- bonds. This suggests that the observed bright O2-induced feature is an intermediate precursor state that may be either a silanone species or a molecular adsorption structure.

Structure and dynamics of biomembranes in room-temperature ionic liquid water solutions studied by neutron scattering and by molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Benedetto, Antonio; Ballone, Pietro

2018-05-01

Increasing attention is being devoted to the interaction of a new class of organic ionic liquids known as room-temperature ionic liquids (RTILs) with biomolecules, partly because of health and environment concerns, and, even more, for the prospect of exciting new applications in biomedicine, sensing and energy technologies. Here we focus on the interaction between RTILs and phospholipid bilayers that are well-accepted models for bio-membranes. We discuss how neutron scattering has been used to probe both the structure and the dynamics of these systems, and how its integration with molecular dynamics simulation has allowed the determination of the microscopic details of their interaction.

Crystal structure and vibrational spectra of piperazinium bis(4-hydroxybenzenesulphonate) molecular-ionic crystal

NASA Astrophysics Data System (ADS)

Marchewka, M. K.; Pietraszko, A.

2008-02-01

The piperazinium bis(4-hydroxybenzenesulphonate) crystallizes from water solution at room temperature in P2 1/ c space group of monoclinic system. The crystals are built up of doubly protonated piperazinium cations and ionized 4-hydroxybenzenesulphonate anions that interact through weak hydrogen bonds of O-H⋯O and N-H⋯O type. Mutual orientation of anions is determined by non-conventional hydrogen bonds of C-H⋯π type. Room temperature powder FT IR and FT Raman measurements were carried out. The vibrational spectra are in full agreement with the structure obtained from X-ray crystallography. The big single crystals of the title salt can be grown.

Multifield Control of Domains in a Room-Temperature Multiferroic 0.85BiTi0.1Fe0.8Mg0.1O3-0.15CaTiO3 Thin Film.

PubMed

Jia, Tingting; Fan, Ziran; Yao, Junxiang; Liu, Cong; Li, Yuhao; Yu, Junxi; Fu, Bi; Zhao, Hongyang; Osada, Minoru; Esfahani, Ehsan Nasr; Yang, Yaodong; Wang, Yuanxu; Li, Jiang-Yu; Kimura, Hideo; Cheng, Zhenxiang

2018-06-20

Single-phase materials that combine electric polarization and magnetization are promising for applications in multifunctional sensors, information storage, spintronic devices, etc. Following the idea of a percolating network of magnetic ions (e.g., Fe) with strong superexchange interactions within a structural scaffold with a polar lattice, a solid solution thin film with perovskite structure at a morphotropic phase boundary with a high level of Fe atoms on the B site of perovskite structure is deposited to combine both ferroelectric and ferromagnetic ordering at room temperature with magnetoelectric coupling. In this work, a 0.85BiTi 0.1 Fe 0.8 Mg 0.1 O 3 -0.15CaTiO 3 thin film has been deposited by pulsed laser deposition (PLD). Both the ferroelectricity and the magnetism were characterized at room temperature. Large polarization and a large piezoelectric effective coefficient d 33 were obtained. Multifield coupling of the thin film has been characterized by scanning force microscopy. Ferroelectric domains and magnetic domains could be switched by magnetic field ( H), electric field ( E), mechanical force ( F), and, indicating that complex cross-coupling exists among the electric polarization, magnetic ordering and elastic deformation in 0.85BiTi 0.1 F e0.8 Mg 0.1 O 3 -0.15CaTiO 3 thin film at room temperature. This work also shows the possibility of writing information with electric field, magnetic field, and mechanical force and then reading data by magnetic field. We expect that this work will benefit information applications.

Fully Stretchable and Humidity-Resistant Quantum Dot Gas Sensors.

PubMed

Song, Zhilong; Huang, Zhao; Liu, Jingyao; Hu, Zhixiang; Zhang, Jianbing; Zhang, Guangzu; Yi, Fei; Jiang, Shenglin; Lian, Jiabiao; Yan, Jia; Zang, Jianfeng; Liu, Huan

2018-05-25

Stretchable gas sensors that accommodate the shape and motion characteristics of human body are indispensable to a wearable or attachable smart sensing system. However, these gas sensors usually have poor response and recovery kinetics when operated at room temperature, and especially suffer from humidity interference and mechanical robustness issues. Here, we demonstrate the first fully stretchable gas sensors which are operated at room temperature with enhanced stability against humidity. We created a crumpled quantum dot (QD) sensing layer on elastomeric substrate with flexible graphene as electrodes. Through the control over the prestrain of the flexible substrate, we achieved a 5.8 times improvement in NO 2 response at room temperature with desirable stretchability even under 1000 stretch/relax cycles mechanism deformation. The uniformly wavy structural configuration of the crumpled QD gas-sensing layer enabled an improvement in the antihumidity interference. The sensor response shows a minor vibration of 15.9% at room temperature from relative humidity of 0 to 86.7% compared to that of the flat-film sensors with vibration of 84.2%. The successful assembly of QD solids into a crumpled gas-sensing layer enabled a body-attachable, mechanically robust, and humidity-resistant gas sensor, opening up a new pathway to room-temperature operable gas sensors which may be implemented in future smart sensing systems such as stretchable electronic nose and multipurpose electronic skin.

Enzyme catalysis captured using multiple structures from one crystal at varying temperatures.

PubMed

Horrell, Sam; Kekilli, Demet; Sen, Kakali; Owen, Robin L; Dworkowski, Florian S N; Antonyuk, Svetlana V; Keal, Thomas W; Yong, Chin W; Eady, Robert R; Hasnain, S Samar; Strange, Richard W; Hough, Michael A

2018-05-01

High-resolution crystal structures of enzymes in relevant redox states have transformed our understanding of enzyme catalysis. Recent developments have demonstrated that X-rays can be used, via the generation of solvated electrons, to drive reactions in crystals at cryogenic temperatures (100 K) to generate 'structural movies' of enzyme reactions. However, a serious limitation at these temperatures is that protein conformational motion can be significantly supressed. Here, the recently developed MSOX (multiple serial structures from one crystal) approach has been applied to nitrite-bound copper nitrite reductase at room temperature and at 190 K, close to the glass transition. During both series of multiple structures, nitrite was initially observed in a 'top-hat' geometry, which was rapidly transformed to a 'side-on' configuration before conversion to side-on NO, followed by dissociation of NO and substitution by water to reform the resting state. Density functional theory calculations indicate that the top-hat orientation corresponds to the oxidized type 2 copper site, while the side-on orientation is consistent with the reduced state. It is demonstrated that substrate-to-product conversion within the crystal occurs at a lower radiation dose at 190 K, allowing more of the enzyme catalytic cycle to be captured at high resolution than in the previous 100 K experiment. At room temperature the reaction was very rapid, but it remained possible to generate and characterize several structural states. These experiments open up the possibility of obtaining MSOX structural movies at multiple temperatures (MSOX-VT), providing an unparallelled level of structural information during catalysis for redox enzymes.

Magnetic and dielectric behavior of chromium substituted Co-Mg ferrite nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jadoun, Priya, E-mail: priya4jadoun@gmail.com; Jyoti,; Prashant, B. L.

The chromium doped Co-Mg ferrite with composition Co{sub 0.5}Mg{sub 0.5}Cr{sub 0.2}Fe{sub 1.8}O{sub 4} has been synthesized using sol-gel auto combustion method. The crystal structure has been analyzed by X-ray diffraction (XRD) technique. XRD pattern reveals the formation of single phase cubic spinel structure. The magnetic measurements show ferromagnetic behavior at room temperature and large coercivity is observed on cooling down the temperature to 20 K. Dielectric constant (ε’) and dielectric loss tangent (tan δ) have been determined at room temperature as a function of frequency in the frequency range 75 kHz to 80 MHz. The decrease in dielectric constant with increasing frequency attributesmore » to Maxwell Wagner model and conduction mechanism in ferrites.« less

Dielectric and magnetic behavior of nanocrystalline Cu{sub 0.4}Co{sub 0.6}Fe{sub 2}O{sub 4} ferrite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jadoun, Priya, E-mail: priya4jadoun@gmail.com; Sharma, Jyoti; Prashant, B. L.

2016-05-23

The mixed copper cobalt ferrite nanoparticles (Cu{sub 0.4}Co{sub 0.6}Fe{sub 2}O{sub 4}) have been synthesized by sol-gel auto combustion route with aqueous metal nitrates and citric acid as the precursor. The crystal structure has been analyzed by X-Ray diffraction (XRD) method. XRD reveals the formation of single phase cubic spinel structure. The Scanning Electron Microscopy (SEM) is used for morphological studies. The dielectric measurements at room temperature show the decrease in dielectric constant with increasing frequency which is attributed to Maxwell Wagner model and conduction mechanism in ferrites.The magnetic measurements show ferromagnetic behavior at room temperature and large coercivity is observedmore » on cooling down the temperature to 20 K.« less

The heat is on: room temperature affects laboratory equipment--an observational study.

PubMed

Butler, Julia M; Johnson, Jane E; Boone, William R

2013-10-01

To evaluate the effect of ambient room temperature on equipment typically used in in vitro fertilization (IVF). We set the control temperature of the room to 20 °C (+/-0.3) and used CIMScan probes to record temperatures of the following equipment: six microscope heating stages, four incubators, five slide warmers and three heating blocks. We then increased the room temperature to 26 °C (+/-0.3) or decreased it to 17 °C (+/-0.3) and monitored the same equipment again. We wanted to determine what role, if any, changing room temperature has on equipment temperature fluctuation. There was a direct relationship between room temperature and equipment temperature stability. When room temperature increased or decreased, equipment temperature reacted in a corresponding manner. Statistical differences between equipment were found when the room temperature changed. What is also noteworthy is that temperature of equipment responded within 5 min to a change in room temperature. Clearly, it is necessary to be aware of the affect of room temperature on equipment when performing assisted reproductive procedures. Room and equipment temperatures should be monitored faithfully and adjusted as frequently as needed, so that consistent culture conditions can be maintained. If more stringent temperature control can be achieved, human assisted reproduction success rates may improve.

Charge Density Wave and Narrow Energy Gap at Room Temperature in 2D Pb 3–xSb 1+xS 4Te 2-δ with Square Te Sheets

DOE PAGES

Chen, Haijie; Malliakas, Christos D.; Narayan, Awadhesh; ...

2017-07-17

We report a new two-dimensional compound Pb 3–xSb 1+xS 4Te 2-δ has a charge density wave (CDW) at room temperature. The CDW is incommensurate with q-vector of 0.248(6)a* + 0.246(8)b* + 0.387(9)c* for x = 0.29(2) and d = 0.37(3) due to positional and occupational long range ordering of Te atoms in the sheets. The modulated structure was refined from the single crystal X-ray diffraction data with a superspace group Pmore » $$\\bar{1}$$(αβγ)0 using (3 + 1)-dimensional crystallography. The resistivity increases with decreasing temperature, suggesting semiconducting behavior. The transition temperature (T CDW) of the CDW is ~ 345 K above which the Te square sheets become disordered with no q-vector. Lastly, first-principles density functional theory calculations on the undistorted structure and an approximate commensurate supercell reveal that the gap is due to the structure modulation.« less

Growth of pentacene on α -Al2O3 (0001) studied by in situ optical spectroscopy

NASA Astrophysics Data System (ADS)

Zhang, Lei; Fu, X.; Hohage, M.; Zeppenfeld, P.; Sun, L. D.

2017-09-01

The growth of pentacene thin films on a sapphire α -Al2O3 (0001) surface was investigated in situ using differential reflectance spectroscopy (DRS). Two different film structures are observed depending on the substrate temperature. If pentacene is deposited at room temperature, a wetting layer consisting of flat-lying molecules is formed after which upright-standing molecular layers with a herringbone structure start to grow. At low substrate temperature of 100 K, the long molecular axis of the pentacene molecules remains parallel to the surface plane throughout the entire growth regime up to rather large thicknesses. Heating thin films deposited at 100 K to room temperature causes the pentacene molecules beyond the wetting layer to stand up and assemble into a herringbone structure. Another interesting observation is the dewetting of the first flat-lying monolayer upon exposure to air, leading to the condensation of islands consisting of upright-standing molecules. Our results emphasize the interplay between growth kinetics and thermodynamics and its influence on the molecular orientation in organic thin films.

Charge Density Wave and Narrow Energy Gap at Room Temperature in 2D Pb 3–xSb 1+xS 4Te 2-δ with Square Te Sheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Haijie; Malliakas, Christos D.; Narayan, Awadhesh

We report a new two-dimensional compound Pb 3–xSb 1+xS 4Te 2-δ has a charge density wave (CDW) at room temperature. The CDW is incommensurate with q-vector of 0.248(6)a* + 0.246(8)b* + 0.387(9)c* for x = 0.29(2) and d = 0.37(3) due to positional and occupational long range ordering of Te atoms in the sheets. The modulated structure was refined from the single crystal X-ray diffraction data with a superspace group Pmore » $$\\bar{1}$$(αβγ)0 using (3 + 1)-dimensional crystallography. The resistivity increases with decreasing temperature, suggesting semiconducting behavior. The transition temperature (T CDW) of the CDW is ~ 345 K above which the Te square sheets become disordered with no q-vector. Lastly, first-principles density functional theory calculations on the undistorted structure and an approximate commensurate supercell reveal that the gap is due to the structure modulation.« less

Charge Density Wave and Narrow Energy Gap at Room Temperature in 2D Pb3-xSb1+xS4Te2-δ with Square Te Sheets.

PubMed

Chen, Haijie; Malliakas, Christos D; Narayan, Awadhesh; Fang, Lei; Chung, Duck Young; Wagner, Lucas K; Kwok, Wai-Kwong; Kanatzidis, Mercouri G

2017-08-16

We report a new two-dimensional compound, Pb 3-x Sb 1+x S 4 Te 2-δ , that has a charge density wave (CDW) at room temperature. The CDW is incommensurate with q-vector of 0.248(6)a* + 0.246(8)b* + 0.387(9)c* for x = 0.29(2) and δ = 0.37(3) due to positional and occupational long-range ordering of Te atoms in the sheets. The modulated structure was refined from the single-crystal X-ray diffraction data with a superspace group P1̅(αβγ)0 using (3 + 1)-dimensional crystallography. The resistivity increases with decreasing temperature, suggesting semiconducting behavior. The transition temperature (T CDW ) of the CDW is ∼345 K, above which the Te square sheets become disordered with no q-vector. First-principles density functional theory calculations on the undistorted structure and an approximate commensurate supercell reveal that the gap is due to the structure modulation.

Property Screening and Evaluation of Ceramic Turbine Materials

DTIC Science & Technology

1984-04-01

Unless otherwise indicated, the upper and lower spans were 0.875 and 1.750 in., respectively. For room-temperature tests, a stainless steel fixture...Silicon Nitride High Temperature Properties Silicon Carbide Silicon Ceramics Transformation-Toughened Zirconia Structural Ceramics Mechanical Properties...3ilicon carbide and silicon nitride, that have potential as structural components in"advanced gas turbine engines, were evaluated. Thermal and

Simultaneous Femtosecond X-ray Spectroscopy and Diffraction of Photosystem II at Room Temperature

PubMed Central

Kern, Jan; Alonso-Mori, Roberto; Tran, Rosalie; Hattne, Johan; Gildea, Richard J.; Echols, Nathaniel; Glöckner, Carina; Hellmich, Julia; Laksmono, Hartawan; Sierra, Raymond G.; Lassalle-Kaiser, Benedikt; Koroidov, Sergey; Lampe, Alyssa; Han, Guangye; Gul, Sheraz; DiFiore, Dörte; Milathianaki, Despina; Fry, Alan R.; Miahnahri, Alan; Schafer, Donald W.; Messerschmidt, Marc; Seibert, M. Marvin; Koglin, Jason E.; Sokaras, Dimosthenis; Weng, Tsu-Chien; Sellberg, Jonas; Latimer, Matthew J.; Grosse-Kunstleve, Ralf W.; Zwart, Petrus H.; White, William E.; Glatzel, Pieter; Adams, Paul D.; Bogan, Michael J.; Williams, Garth J.; Boutet, Sébastien; Messinger, Johannes; Zouni, Athina; Sauter, Nicholas K.; Yachandra, Vittal K.; Bergmann, Uwe; Yano, Junko

2013-01-01

Intense femtosecond X-ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous X-ray diffraction (XRD) and X-ray emission spectroscopy (XES) of microcrystals of Photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S1) and the first illuminated state (S2) of PS II. Our simultaneous XRD/XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies. PMID:23413188

Simultaneous femtosecond X-ray spectroscopy and diffraction of photosystem II at room temperature.

PubMed

Kern, Jan; Alonso-Mori, Roberto; Tran, Rosalie; Hattne, Johan; Gildea, Richard J; Echols, Nathaniel; Glöckner, Carina; Hellmich, Julia; Laksmono, Hartawan; Sierra, Raymond G; Lassalle-Kaiser, Benedikt; Koroidov, Sergey; Lampe, Alyssa; Han, Guangye; Gul, Sheraz; Difiore, Dörte; Milathianaki, Despina; Fry, Alan R; Miahnahri, Alan; Schafer, Donald W; Messerschmidt, Marc; Seibert, M Marvin; Koglin, Jason E; Sokaras, Dimosthenis; Weng, Tsu-Chien; Sellberg, Jonas; Latimer, Matthew J; Grosse-Kunstleve, Ralf W; Zwart, Petrus H; White, William E; Glatzel, Pieter; Adams, Paul D; Bogan, Michael J; Williams, Garth J; Boutet, Sébastien; Messinger, Johannes; Zouni, Athina; Sauter, Nicholas K; Yachandra, Vittal K; Bergmann, Uwe; Yano, Junko

2013-04-26

Intense femtosecond x-ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous x-ray diffraction (XRD) and x-ray emission spectroscopy (XES) of microcrystals of photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S1) and the first illuminated state (S2) of PS II. Our simultaneous XRD-XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.

Dimer formation and surface alloying: a STM study of lead on Cu(211)

NASA Astrophysics Data System (ADS)

Bartels, L.; Zöphel, S.; Meyer, G.; Henze, E.; Rieder, K.-H.

1997-02-01

We present a STM investigation of Pb adsorption on the Cu(211) surface in the temperature range between 30 K and room temperature. We observe three different kinds of ordered 1D Pb and PbCu chains (nanowires) located at the intrinsic step edges of the Cu(211) surface. On room temperature prepared samples, Pb is found to be incorporated into the step edges of the (211) surface. The first ordered structure consists of CuPb chains at the step edges (p(2 × disorder)) and is followed with increasing coverage by a close packed row of Pb-atoms (p(4 × disorder)). Preparation at low temperature yields Pb-dimers, and the first ordered structure is a row of Pb-dimers at the step edge (p(3 × disorder)) followed with increased coverage by a structure as described above. By systematic manipulation with the tunneling tip, we could get additional insight into the structural elements of the PbCu layer on the atomic scale. Furthermore, by measuring the threshold resistance to detach atoms from different ad-sites, we can approximately determine the binding energy and gain some insight into the thermodynamical parameters involved.

Mechanical Properties of the TiAl IRIS Alloy

NASA Astrophysics Data System (ADS)

Voisin, Thomas; Monchoux, Jean-Philippe; Thomas, Marc; Deshayes, Christophe; Couret, Alain

2016-12-01

This paper presents a study of the mechanical properties at room and high temperature of the boron and tungsten containing IRIS alloy (Ti-48Al-2W-0.08B at. pct). This alloy was densified by Spark Plasma Sintering (SPS). The resultant microstructure consists of small lamellar colonies surrounded by γ regions containing B2 precipitates. Tensile tests are performed from room temperature to 1273 K (1000 °C). Creep properties are determined at 973 K (700 °C)/300 MPa, 1023 K (750 °C)/120 MPa, and 1023 K (750 °C)/200 MPa. The tensile strength and the creep resistance at high temperature are found to be very high compared to the data reported in the current literature while a plastic elongation of 1.6 pct is preserved at room temperature. A grain size dependence of both ductility and strength is highlighted at room temperature. The deformation mechanisms are studied by post-mortem analyses on deformed samples and by in situ straining experiments, both performed in a transmission electron microscope. In particular, a low mobility of non-screw segments of dislocations at room temperature and the activation of a mixed-climb mechanism during creep have been identified. The mechanical properties of this IRIS alloy processed by SPS are compared to those of other TiAl alloys developed for high-temperature structural applications as well as to those of similar tungsten containing alloys obtained by more conventional processing techniques. Finally, the relationships between mechanical properties and microstructural features together with the elementary deformation mechanisms are discussed.

Room temperature ferromagnetism in Mn-doped NiO nanoparticles

NASA Astrophysics Data System (ADS)

Layek, Samar; Verma, H. C.

2016-01-01

Mn-doped NiO nanoparticles of the series Ni1-xMnxO (x=0.00, 0.02, 0.04 and 0.06) are successfully synthesized using a low temperature hydrothermal method. Samples up to 6% Mn-doping are single phase in nature as observed from powder x-ray diffraction (XRD) studies. Rietveld refinement of the XRD data shows that all the single phase samples crystallize in the NaCl like fcc structure with space group Fm-3m. Unit cell volume decreases with increasing Mn-doping. Pure NiO nanoparticles show weak ferromagnetism, may be due to nanosize nature. Introduction of Mn within NiO lattice improves the magnetic properties significantly. Room temperature ferromagnetism is found in all the doped samples whereas the magnetization is highest for 2% Mn-doping and then decreases with further doping. The ZFC and FC branches in the temperature dependent magnetization separate well above 350 K indicating transition temperature well above room temperature for 2% Mn-doped NiO Nanoparticle. The ferromagnetic Curie temperature is found to be 653 K for the same sample as measured by temperature dependent magnetization study using vibrating sample magnetometer (VSM) in high vacuum.

Piezoelectric paints as one approach to smart structural materials with health-monitoring capabilities

NASA Astrophysics Data System (ADS)

Egusa, Shigenori; Iwasawa, Naozumi

1998-08-01

Piezoelectric paints have a potential to change a conventional structural material into an intelligent material system with health-monitoring capabilities such as vibration sensing and damage detection. Such paints were prepared using lead zirconate titanate (PZT) ceramic powder as a pigment and epoxy resin as a binder. The obtained paints were coated on aluminum test specimens, and were cured at room temperature or at 150 0964-1726/7/4/002/img5, thus forming the paint films having different thicknesses of 25-300 0964-1726/7/4/002/img6. These films were then poled at room temperature, and were evaluated with regard to the sensitivities as vibration and acoustic emission sensors in the frequency ranges of 0-250 Hz and 0-1.0 MHz, respectively. This paper mainly describes the effects of the film thickness and the cure temperature on the poling behavior of the PZT/epoxy paint film. This paper describes also the application of the paint film as a vibration modal sensor integrated into a structural material.

Ferromagnetism appears in nitrogen implanted nanocrystalline diamond films

NASA Astrophysics Data System (ADS)

Remes, Zdenek; Sun, Shih-Jye; Varga, Marian; Chou, Hsiung; Hsu, Hua-Shu; Kromka, Alexander; Horak, Pavel

2015-11-01

The nanocrystalline diamond films turn to be ferromagnetic after implanting various nitrogen doses on them. Through this research, we confirm that the room-temperature ferromagnetism of the implanted samples is derived from the measurements of magnetic circular dichroism (MCD) and superconducting quantum interference device (SQUID). Samples with larger crystalline grains as well as higher implanted doses present more robust ferromagnetic signals at room temperature. Raman spectra indicate that the small grain-sized samples are much more disordered than the large grain-sized ones. We propose that a slightly large saturated ferromagnetism could be observed at low temperature, because the increased localization effects have a significant impact on more disordered structure.

Experimental Study of a Hot Structure for a Reentry Vehicle

NASA Technical Reports Server (NTRS)

Pride, Richard A.; Royster, Dick M.; Helms, Bobbie F.

1960-01-01

A large structural model of a reentry vehicle has been built incorporating design concepts applicable to a radiation-cooled vehicle. Thermal-stress alleviating features of the model are discussed. Environmental tests on the model include approximately 100 cycles of loading at room temperature and 33 cycles of combined loading and-heating up to temperatures of 1,6000 F. Measured temperatures are shown for typical parts of the model. Comparisons are made between experimental and calculated deflections and strains. The structure successfully survived the heating and loading environments.

Fe-Al alloy single-crystal thin film preparation for basic magnetic measurements

NASA Astrophysics Data System (ADS)

Abe, Tatsuya; Kawai, Tetsuroh; Futamoto, Masaaki; Ohtake, Mitsuru; Inaba, Nobuyuki

2018-04-01

Fe100-xAlx (x = 0, 4, 10, 20, 30 at. %) alloy films of 40 nm thickness are prepared on MgO(001) single-crystal substrates by varying substrate temperature from room temperature to 600 °C. Single-crystal films of (001) orientation with bcc-based disordered A2 structure are obtained for the Al content range of x = 0 - 20 at. %. An ordered phase of DO3 structure is observed in Fe70Al30 films prepared at temperatures higher than 200 °C, whereas (001) oriented single-crystal films of A2 structure are obtained when prepared at room temperature. The film surface profile does not depend much on the film composition, while the surface roughness increases with increasing substrate temperature. Island-like crystals are observed for films prepared at 600°C for all compositions. Difference in lattice spacing measured parallel and perpendicular to the substrate is noted for the single-crystal thin films and it increases with increasing Al content. The lattice strain in single-crystal film is caused possibly to accommodate the lattice mismatch with the MgO substrate. The (001)-oriented single-crystal films with A2 structure show four-fold symmetries in in-plane magnetic anisotropy with the easy magnetization axis A2[100] and the hard magnetization axis A2[110], whereas the films with DO3 ordered structure show almost isotropic magnetic properties.

Structure of Ce2RhIn8: an example of complementary use of high-resolution neutron powder diffraction and reciprocal-space mapping to study complex materials.

PubMed

Moshopoulou, E G; Ibberson, R M; Sarrao, J L; Thompson, J D; Fisk, Z

2006-04-01

The room-temperature crystal structure of the heavy fermion antiferromagnet Ce2RhIn8, dicerium rhodium octaindide, has been studied by a combination of high-resolution synchrotron X-ray reciprocal-space mapping of single crystals and high-resolution time-of-flight neutron powder diffraction. The structure is disordered, exhibiting a complex interplay of non-periodic, partially correlated planar defects, coexistence and segregation of polytypic phases (induced by periodic planar ;defects'), mosaicity (i.e. domain misalignment) and non-uniform strain. These effects evolve as a function of temperature in a complicated way, but they remain down to low temperatures. The room-temperature diffraction data are best represented by a complex mixture of two polytypic phases, which are affected by non-periodic, partially correlated planar defects, differ slightly in their tetragonal structures, and exhibit different mosaicities and strain values. Therefore, Ce2RhIn8 approaches the paracrystalline state, rather than the classic crystalline state and thus several of the concepts of conventional single-crystal crystallography are inapplicable. The structural results are discussed in the context of the role of disorder in the heavy-fermion state and in the interplay between superconductivity and magnetism.

Enhancement of ferromagnetic properties in composites of BaSnO3 and CoFe2O4

NASA Astrophysics Data System (ADS)

Manju, M. R.; Ajay, K. S.; D'Souza, Noel M.; Hunagund, Shivakumar; Hadimani, R. L.; Dayal, Vijaylakshmi

2018-04-01

In this paper, we report structural and magnetic properties of BaSnO3(BSO)(1-x)-CoFe2O4 (CFO)(x) composite (with x = 0%, 1% (C1), 2% (C2) and 5% (C3) in molar ratio) synthesized using nitrate precursor method. The X-ray diffraction (XRD) pattern of the composite powder confirmed presence of both BaSnO3 with the cubic perovskite structure and CoFe2O4 with the cubic spinel structure. No signature of any other phases in pure BaSnO3, CoFe2O4 and composites have been detected either in XRD or energy dispersive X-ray (EDS) analysis. The temperature dependent zero field cooled (ZFC) & field cooled (FC) magnetization and magnetic field dependence magnetization measurements have been carried at room temperature of the pure BaSnO3. We observe a weak ferromagnetic (FM) behavior at room temperature in pure BaSnO3 even though it is non-magnetic in nature. The room temperature Raman spectroscopy and electron spin resonance measurements of the sample confirm the presence of oxygen vacancy and formation of F-center, which is responsible for the FM behavior. The oxidation state and elemental analysis have been carried out using X-ray photoelectron spectroscopy (XPS). The magnetic field dependence of magnetization of the composite samples reveal increase of saturation magnetization (Ms), remanence magnetization (Mr) and coercivity (Hc) with increase in ferrite content in the composite. Significant enhancement in FM components is observed with lowering of temperature.

Fluorescence x-ray absorption fine structure studies of Fe-Ni-S and Fe-Ni-Si melts to 1600 K

NASA Astrophysics Data System (ADS)

Manghnani, M. H.; Hong, X.; Balogh, J.; Amulele, G.; Sekar, M.; Newville, M.

2008-04-01

We report NiK -edge fluorescence x-ray absorption fine structure spectra (XAFS) for Fe0.75Ni0.05S0.20 and Fe0.75Ni0.05Si0.20 ternary alloys from room temperature up to 1600 K. A high-temperature furnace designed for these studies incorporates two x-ray transparent windows and enables both a vertical orientation of the molten sample and a wide opening angle, so that XAFS can be measured in the fluorescence mode with a detector at 90° with respect to the incident x-ray beam. An analysis of the Ni XAFS data for these two alloys indicates different local structural environments for Ni in Fe0.75Ni0.05S0.20 and Fe0.75Ni0.05Si0.20 melts, with more Ni-Si coordination than Ni-S coordination persisting from room temperature through melting. These results suggest that light elements such as S and Si may impact the structural and chemical properties of Fe-Ni alloys with a composition similar to the earth’s core.

Properties of cryogenically worked metals. [stainless steels

NASA Technical Reports Server (NTRS)

Schwartzberg, F. R.; Kiefer, T. F.

1975-01-01

A program was conducted to determine whether the mechanical properties of cryogenically worked 17-7PH stainless steel are suitable for service from ambient to cryogenic temperatures. It was determined that the stress corrosion resistance of the cryo-worked material is quite adequate for structural service. The tensile properties and fracture toughness at room temperature were comparable to titanium alloy 6Al-4V. However, at cryogenic temperatures, the properties were not sufficient to recommend consideration for structural service.

Evolution of structure and magnetic properties for BaFe11.9Al0.1O19 hexaferrite in a wide temperature range

NASA Astrophysics Data System (ADS)

Trukhanov, A. V.; Trukhanov, S. V.; Panina, L. V.; Kostishyn, V. G.; Kazakevich, I. S.; Trukhanov, An. V.; Trukhanova, E. L.; Natarov, V. O.; Turchenko, V. A.; Salem, M. M.; Balagurov, A. M.

2017-03-01

M-type BaFe11.9Al0.1O19 hexaferrite was successfully synthesized by solid state reactions. Precision investigations of crystal and magnetic structures of BaFe11.9Al0.1O19 powder by neutron diffraction in the temperature range 4.2-730 K have been performed. Magnetic and electrical properties investigations were carried out in the wide temperature range. Neutron powder diffraction data were successfully refined in approximation for both space groups (SG): centrosymmetric #194 (standard non-polar phase) and non-centrosymmetric #186 (polar phase). It has been shown that at low temperatures (below room temperature) better fitting results (value χ2) were for the polar phase (SG: #186) or for the two phases coexistence (SG: #186 and SG: #194). At high temperatures (400-730 K) better fitting results were for SG: #194. It was established coexistence of the dual ferroic properties (specific magnetization and spontaneous polarization) at room temperature. Strong correlation between magnetic and electrical subsystems was demonstrated (magnetoelectrical effect). Temperature dependences of the spontaneous polarization, specific magnetization and magnetoelectrical effect were investigated.

Gapped electronic structure of epitaxial stanene on InSb(111)

DOE PAGES

Xu, Cai-Zhi; Chan, Yang-Hao; Chen, Peng; ...

2018-01-11

We report that stanene (single-layer gray tin), with an electronic structure akin to that of graphene but exhibiting a much larger spin-orbit gap, offers a promising platform for room-temperature electronics based on the quantum spin Hall (QSH) effect. This material has received much theoretical attention, but a suitable substrate for stanene growth that results in an overall gapped electronic structure has been elusive; a sizable gap is necessary for room-temperature applications. Here, we report a study of stanene, epitaxially grown on the (111)B-face of indium antimonide (InSb). Angle-resolved photoemission spectroscopy measurements reveal a gap of 0.44 eV, in agreement withmore » our first-principles calculations. Lastly, the results indicate that stanene on InSb(111) is a strong contender for electronic QSH applications.« less

Gapped electronic structure of epitaxial stanene on InSb(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Cai-Zhi; Chan, Yang-Hao; Chen, Peng

We report that stanene (single-layer gray tin), with an electronic structure akin to that of graphene but exhibiting a much larger spin-orbit gap, offers a promising platform for room-temperature electronics based on the quantum spin Hall (QSH) effect. This material has received much theoretical attention, but a suitable substrate for stanene growth that results in an overall gapped electronic structure has been elusive; a sizable gap is necessary for room-temperature applications. Here, we report a study of stanene, epitaxially grown on the (111)B-face of indium antimonide (InSb). Angle-resolved photoemission spectroscopy measurements reveal a gap of 0.44 eV, in agreement withmore » our first-principles calculations. Lastly, the results indicate that stanene on InSb(111) is a strong contender for electronic QSH applications.« less

Lipidic cubic phase serial millisecond crystallography using synchrotron radiation

PubMed Central

Nogly, Przemyslaw; James, Daniel; Wang, Dingjie; White, Thomas A.; Zatsepin, Nadia; Shilova, Anastasya; Nelson, Garrett; Liu, Haiguang; Johansson, Linda; Heymann, Michael; Jaeger, Kathrin; Metz, Markus; Wickstrand, Cecilia; Wu, Wenting; Båth, Petra; Berntsen, Peter; Oberthuer, Dominik; Panneels, Valerie; Cherezov, Vadim; Chapman, Henry; Schertler, Gebhard; Neutze, Richard; Spence, John; Moraes, Isabel; Burghammer, Manfred; Standfuss, Joerg; Weierstall, Uwe

2015-01-01

Lipidic cubic phases (LCPs) have emerged as successful matrixes for the crystallization of membrane proteins. Moreover, the viscous LCP also provides a highly effective delivery medium for serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs). Here, the adaptation of this technology to perform serial millisecond crystallography (SMX) at more widely available synchrotron microfocus beamlines is described. Compared with conventional microcrystallography, LCP-SMX eliminates the need for difficult handling of individual crystals and allows for data collection at room temperature. The technology is demonstrated by solving a structure of the light-driven proton-pump bacteriorhodopsin (bR) at a resolution of 2.4 Å. The room-temperature structure of bR is very similar to previous cryogenic structures but shows small yet distinct differences in the retinal ligand and proton-transfer pathway. PMID:25866654

Silicon-germanium and platinum silicide nanostructures for silicon based photonics

NASA Astrophysics Data System (ADS)

Storozhevykh, M. S.; Dubkov, V. P.; Arapkina, L. V.; Chizh, K. V.; Mironov, S. A.; Chapnin, V. A.; Yuryev, V. A.

2017-05-01

This paper reports a study of two types of silicon based nanostructures prospective for applications in photonics. The first ones are Ge/Si(001) structures forming at room temperature and reconstructing after annealing at 600°C. Germanium, being deposited from a molecular beam at room temperature on the Si(001) surface, forms a thin granular film composed of Ge particles with sizes of a few nanometers. A characteristic feature of these films is that they demonstrate signs of the 2 x 1 structure in their RHEED patterns. After short-term annealing at 600°C under the closed system conditions, the granular films reconstruct to heterostructures consisting of a Ge wetting layer and oval clusters of Ge. A mixed type c(4x2) + p(2x2) reconstruction typical to the low-temperature MBE (Tgr < 600°C) forms on the wetting layer. Long-term annealing of granular films at the same conditions results in formation of c(4x2)-reconstructed wetting layer typical to high-temperature MBE (Tgr < 600°C) and huge clusters of Ge. The other type of the studied nanostructures is based on Pt silicides. This class of materials is one of the friendliest to silicon technology. But as silicide film thickness reaches a few nanometers, low resistivity becomes of primary importance. Pt3Si has the lowest sheet resistance among the Pt silicides. However, the development of a process of thin Pt3Si films formation is a challenging task. This paper describes formation of a thin Pt3Si/Pt2Si structures at room temperature on poly-Si films. Special attention is paid upon formation of poly-Si and amorphous Si films on Si3N4 substrates at low temperatures.

Room temperature exchange bias in multiferroic BiFeO3 nano- and microcrystals with antiferromagnetic core and two-dimensional diluted antiferromagnetic shell

NASA Astrophysics Data System (ADS)

Zhang, Chuang; Wang, Shou Yu; Liu, Wei Fang; Xu, Xun Ling; Li, Xiu; Zhang, Hong; Gao, Ju; Li, De Jun

2017-05-01

Exchange bias (EB) of multiferroics presents many potential opportunities for magnetic devices. However, instead of using low-temperature field cooling in the hysteresis loop measurement, which usually shows an effective approach to obtain obvious EB phenomenon, there are few room temperature EB. In this article, extensive studies on room temperature EB without field cooling were observed in BiFeO3 nano- and microcrystals. Moreover, with increasing size the hysteresis loops shift from horizontal negative exchange bias (NEB) to positive exchange bias (PEB). In order to explain the tunable EB behaviors with size dependence, a phenomenological qualitative model based on the framework of antiferromagnetic (AFM) core-two-dimensional diluted antiferromagnet in a field (2D-DAFF) shell structure was proposed. The training effect (TE) ascertained the validity of model and the presence of unstable magnetic structure using Binek's model. Experimental results show that the tunable EB effect can be explained by the competition of ferromagnetic (FM) exchange coupling and AFM exchange coupling interaction between AFM core and 2D-DAFF shell. Additionally, the local distortion of lattice fringes was observed in hexagonal-shaped BiFeO3 nanocrystals with well-dispersed behavior. The electrical conduction properties agreed well with the space charge-limited conduction mechanism.

Self-assembled novel multi-porphyrin micro-crystals as a photocatalyst for 2,4,6-trinitrotoluene degradation

NASA Astrophysics Data System (ADS)

Hikal, Walid M.

In this thesis I have presented the findings of my research pursued during my Ph.D. study. Following the findings that 2,4,6-trinitrotoluene binds to porphyrins at room temperature and could be photoctalytically degraded using porphyrin solutions and visible light, the purpose of this work was to determine the nature of the binding between the two species and develop a solid porphyrin-based photocatalyst for TNT degradation. C1TPP porphyrin is found to be able to bind to TNT via 1.94 kcal/mole hydrogen bonds at room temperature and hydrophobic bonds at higher temperatures. Photocatalytic solid porphyrin crystalline structures have been developed using two oppositely charged, commercially available, and low cost porphyrins in presence and absence of PAMAM generation 4 (G4) dendrimer, by self-assembly at room temperature without acidification. Solid porphyrin crystals were characterized by means of optical microscopy, UV-visible spectroscopy, fluorescence spectroscopy, and powder X-ray diffraction. A hypothetical model for the structure of the crystals is proposed. The porphyrin crystals show photocatalytic capabilities; illumination of the crystals in a 2,4,6-trinitrotoluene solution by visible light results in degradation of TNT and the intermediates have been determined using high pressure liquid chromatography (HPLC) and gas chromatography (GC).

Room-temperature voltage tunable phonon thermal conductivity via reconfigurable interfaces in ferroelectric thin films.

PubMed

Ihlefeld, Jon F; Foley, Brian M; Scrymgeour, David A; Michael, Joseph R; McKenzie, Bonnie B; Medlin, Douglas L; Wallace, Margeaux; Trolier-McKinstry, Susan; Hopkins, Patrick E

2015-03-11

Dynamic control of thermal transport in solid-state systems is a transformative capability with the promise to propel technologies including phononic logic, thermal management, and energy harvesting. A solid-state solution to rapidly manipulate phonons has escaped the scientific community. We demonstrate active and reversible tuning of thermal conductivity by manipulating the nanoscale ferroelastic domain structure of a Pb(Zr0.3Ti0.7)O3 film with applied electric fields. With subsecond response times, the room-temperature thermal conductivity was modulated by 11%.

Investigation of a Structural Phase Transition and Magnetic Structure of Na 2BaFe(VO 4) 2: A Triangular Magnetic Lattice with a Ferromagnetic Ground State

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanjeewa, Liurukara D.; Garlea, Vasile O.; McGuire, Michael A.

The structural and magnetic properties of a glaserite-type Na 2BaFe(VO 4) 2 compound, featuring a triangular magnetic lattice of Fe 2+ (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal Pmore » $$\\bar{3}$$ m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (T s = 288 K). This structural transition involves a tilting of Fe–O–V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in Na 2BaFe(VO 4) 2. The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Altogether, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO 6 octahedron.« less

Investigation of a Structural Phase Transition and Magnetic Structure of Na 2BaFe(VO 4) 2: A Triangular Magnetic Lattice with a Ferromagnetic Ground State

DOE PAGES

Sanjeewa, Liurukara D.; Garlea, Vasile O.; McGuire, Michael A.; ...

2017-12-07

The structural and magnetic properties of a glaserite-type Na 2BaFe(VO 4) 2 compound, featuring a triangular magnetic lattice of Fe 2+ (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal Pmore » $$\\bar{3}$$ m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (T s = 288 K). This structural transition involves a tilting of Fe–O–V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in Na 2BaFe(VO 4) 2. The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Altogether, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO 6 octahedron.« less

Pressure-induced photoluminescence in Mn2+-doped BaF2 and SrF2 fluorites

NASA Astrophysics Data System (ADS)

Hernández, Ignacio; Rodríguez, Fernando

2003-01-01

This work reports an effective way for inducing room temperature photoluminescence (PL) in Mn2+-doped BaF2 and SrF2 using high-pressure techniques. The aim is to understand the surprising PL behavior exhibited by Mn2+ at the cubal site of the fluorite structure. While Mn2+-doped CaF2 shows a green PL with quantum yield close to 1 at room temperature, Mn2+-doped MF2 (M=Ba,Sr) is not PL either at room temperature (SrF2) or at any temperature (BaF2) at ambient pressure. We associate the loss of Mn2+ PL on passing from CaF2 to SrF2 or BaF2 with nonradiative multiphonon relaxation whose thermal activation energy decreases along the series CaF2→SrF2→BaF2. A salient feature of this work deals with the increase of activation energy induced by pressure. It leads to a quantum yield enhancement, which favors PL recovery. Furthermore, the activation energy mainly depends on the crystal volume per molecule irrespective of the crystal structure or the local symmetry around the impurity. In this way, the relevance of the fluorite-to-cotunnite phase transition is analyzed in connection with the PL properties of the investigated compounds. The PL spectrum and the corresponding lifetime are reported for both structural phases as a function of pressure.

Strain-engineering stabilization of BaTi O3 -based polar metals

NASA Astrophysics Data System (ADS)

Ma, Chao; Jin, Kui-juan; Ge, Chen; Yang, Guo-zhen

2018-03-01

Polar metals, which possess ferroelectriclike polar structure and conductivity simultaneously, have attracted wide interest since the first solid example, LiOs O3 (below 140 K), was discovered. However, the lack of room-temperature polar metals hinders further research and applications. Thus abundant properties of polar metals are unexplored. Here, with first-principles calculations, we report that the polar metal phase can be stabilized in the strain-engineered BaTi O3 with electron doping. The mechanism relates to the competition between the shifting of the t2 g energy levels and the narrowing of their bandwidth. Surprisingly, it is predicted that the ferroelectric-to-paraelectric transition temperature can be increased by electron doping when the strain is large enough, which holds potential for room-temperature polar metals. Our results indicate that strain engineering is a promising way to achieve BaTi O3 -based polar metals, and they should have practical significance for obtaining easily accessible, ecofriendly, and potential room-temperature polar metals.

Atomistic structures of nano-engineered SiC and radiation-induced amorphization resistance

NASA Astrophysics Data System (ADS)

Imada, Kenta; Ishimaru, Manabu; Sato, Kazuhisa; Xue, Haizhou; Zhang, Yanwen; Shannon, Steven; Weber, William J.

2015-10-01

Nano-engineered 3C-SiC thin films, which possess columnar structures with high-density stacking faults and twins, were irradiated with 2 MeV Si ions at cryogenic and room temperatures. From cross-sectional transmission electron microscopy observations in combination with Monte Carlo simulations based on the Stopping and Range of Ions in Matter code, it was found that their amorphization resistance is six times greater than bulk crystalline SiC at room temperature. High-angle bright-field images taken by spherical aberration corrected scanning transmission electron microscopy revealed that the distortion of atomic configurations is localized near the stacking faults. The resultant strain field probably contributes to the enhancement of radiation tolerance of this material.

Three-dimensional spin mapping of antiferromagnetic nanopyramids having spatially alternating surface anisotropy at room temperature.

PubMed

Wang, Kangkang; Smith, Arthur R

2012-11-14

Antiferromagnets play a key role in modern spintronic devices owing to their ability to modify the switching behavior of adjacent ferromagnets via the exchange bias effect. Consequently, detailed measurements of the spin structure at antiferromagnetic interfaces and surfaces are highly desirable, not only for advancing technologies but also for enabling new insights into the underlying physics. Here using spin-polarized scanning tunneling microscopy at room-temperature, we reveal in three-dimensions an orthogonal spin structure on antiferromagnetic compound nanopyramids. Contrary to expected uniaxial anisotropy based on bulk properties, the atomic terraces are found to have alternating in-plane and out-of-plane magnetic anisotropies. The observed layer-wise alternation in anisotropy could have strong influences on future nanoscale spintronic applications.

Guanidinium-Formamidinium Lead Iodide: A Layered Perovskite-Related Compound with Red Luminescence at Room Temperature.

PubMed

Nazarenko, Olga; Kotyrba, Martin R; Yakunin, Sergii; Aebli, Marcel; Rainò, Gabriele; Benin, Bogdan M; Wörle, Michael; Kovalenko, Maksym V

2018-03-21

Two-dimensional hybrid organic-inorganic lead halides perovskite-type compounds have attracted immense scientific interest due to their remarkable optoelectronic properties and tailorable crystal structures. In this work, we present a new layered hybrid lead halide, namely [CH(NH 2 ) 2 ][C(NH 2 ) 3 ]PbI 4 , wherein puckered lead-iodide layers are separated by two small and stable organic cations: formamidinium, CH(NH 2 ) 2 + , and guanidinium, C(NH 2 ) 3 + . This perovskite is thermally stable up to 255 °C, exhibits room-temperature photoluminescence in the red region with a quantum yield of 3.5%, and is photoconductive. This study highlights a vast structural diversity that exists in the compositional space typically used in perovskite photovoltaics.

On the possibility of room temperature ferromagnetism on chunk-shape BaSnO3/ZnO core/shell nanostructures

NASA Astrophysics Data System (ADS)

Rajamanickam, N.; Jayakumar, K.; Ramachandran, K.

2018-04-01

Core/shell BaSnO3/ZnO (BS-ZO) nanostructures were prepared by oxalate precipitation method and wet-chemical method. BaSnO3 (BSO) cubic perovskite structure and ZnO hexagonal wurtzite structure were confirmed by X-ray diffraction (XRD). The crystallite sizes is 23 nm, 29 nm and 27 nm for BSO, ZnO and BS-ZO, respectively. Chunk-shape and cuboids morphology observed from scanning electron microscopy (SEM) analysis. The magnetic properties were studied by VSM for bare and core-shell nano systems and the room temperature ferromagnetism observed for core-shell nanostructures. The BSO/ZnO shows enhanced coercivity and saturated magnetization as compared with BSO and ZnO nanostructures.

Efficient room temperature hydrogen sensor based on UV-activated ZnO nano-network

NASA Astrophysics Data System (ADS)

Kumar, Mohit; Kumar, Rahul; Rajamani, Saravanan; Ranwa, Sapana; Fanetti, Mattia; Valant, Matjaz; Kumar, Mahesh

2017-09-01

Room temperature hydrogen sensors were fabricated from Au embedded ZnO nano-networks using a 30 mW GaN ultraviolet LED. The Au-decorated ZnO nano-networks were deposited on a SiO2/Si substrate by a chemical vapour deposition process. X-ray diffraction (XRD) spectrum analysis revealed a hexagonal wurtzite structure of ZnO and presence of Au. The ZnO nanoparticles were interconnected, forming nano-network structures. Au nanoparticles were uniformly distributed on ZnO surfaces, as confirmed by FESEM imaging. Interdigitated electrodes (IDEs) were fabricated on the ZnO nano-networks using optical lithography. Sensor performances were measured with and without UV illumination, at room temperate, with concentrations of hydrogen varying from 5 ppm to 1%. The sensor response was found to be ˜21.5% under UV illumination and 0% without UV at room temperature for low hydrogen concentration of 5 ppm. The UV-photoactivated mode enhanced the adsorption of photo-induced O- and O2- ions, and the d-band electron transition from the Au nanoparticles to ZnO—which increased the chemisorbed reaction between hydrogen and oxygen. The sensor response was also measured at 150 °C (without UV illumination) and found to be ˜18% at 5 ppm. Energy efficient low cost hydrogen sensors can be designed and fabricated with the combination of GaN UV LEDs and ZnO nanostructures.

Effect of strain on the Curie temperature and band structure of low-dimensional SbSI

NASA Astrophysics Data System (ADS)

Wang, Yiping; Hu, Yang; Chen, Zhizhong; Guo, Yuwei; Wang, Dong; Wertz, Esther A.; Shi, Jian

2018-04-01

Photoferroelectric materials show great promise for developing alternative photovoltaics and photovoltaic-type non-volatile memories. However, the localized nature of the d orbital and large bandgap of most natural photoferroelectric materials lead to low electron/hole mobility and limit the realization of technologically practical devices. Antimony sulpho-iodide (SbSI) is a photoferroelectric material which is expected to have high electron/hole mobility in the ferroelectric state due to its non-local band dispersion and narrow bandgap. However, SbSI exhibits the paraelectric state close to room temperature. In this report, as a proof of concept, we explore the possibility to stabilize the SbSI ferroelectric phase above room temperature via mechanical strain engineering. We synthesized thin low-dimensional crystals of SbSI by chemical vapor deposition, confirmed its crystal structure with electron diffraction, studied its optical properties via photoluminescence spectroscopy and time-resolved photoluminescence spectroscopy, and probed its phase transition using temperature-dependent steady-state photoluminescence spectroscopy. We found that introducing external mechanical strain to these low-dimensional crystals may lead to an increase in their Curie temperature (by ˜60 K), derived by the strain-modified optical phase transition in SbSI and quantified by Kern formulation and Landau theory. The study suggests that strain engineering could be an effective way to stabilize the ferroelectric phase of SbSI at above room temperature, providing a solution enabling its application for technologically useful photoferroelectric devices.

Fabrication of a microfluidic chip by UV bonding at room temperature for integration of temperature-sensitive layers

NASA Astrophysics Data System (ADS)

Schlautmann, S.; Besselink, G. A. J.; Radhakrishna Prabhu, G.; Schasfoort, R. B. M.

2003-07-01

A method for the bonding of a microfluidic device at room temperature is presented. The wafer with the fluidic structures was bonded to a sensor wafer with gold pads by means of adhesive bonding, utilizing an UV-curable glue layer. To avoid filling the fluidic channels with the glue, a stamping process was developed which allows the selective application of a thin glue layer. In this way a microfluidic glass chip was fabricated that could be used for performing surface plasmon resonance measurements without signs of leakage. The advantage of this method is the possibility of integration of organic layers as well as other temperature-sensitive layers into a microfluidic glass device.

Correlation of mechanical properties with metallurgical structure for 18Ni 200 grade maraging steel at room and cryogenic temperatures

NASA Technical Reports Server (NTRS)

Wagner, J. A.

1991-01-01

An extensive metallurgical study is presented which is intended to explain variations in the mechanical properties of Ni18 200 grade maraging steel in various product forms and orientations. Fracture toughness and Charpy impact values are found to decrease with decreasing temperature and be dependent on product form, specimen orientation, and metallurgical condition. Fatigue crack growth rates are dependent on temperature only. Fractographic analysis reveals that the decrease in toughness at -170 C is not associated with cleavage-type fracture morphology. Those specimens exhibiting low fracture toughness at room temperature or -170 C are found to have a significantly larger number of titanium-rich particles associated with dimple formation on the fracture surface.

P-type sub-tungsten-oxide based urchin-like nanostructure for superior room temperature alcohol sensor

NASA Astrophysics Data System (ADS)

Yao, Yao; Yin, Mingli; Yan, Junqing; Liu, Shengzhong (Frank)

2018-05-01

Nanowires assembled sub-WO3 urchin-like nanostructures have been fabricated via a solvothermal method. The detailed structure and morphology features were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The results reveal that the individual nanowires are grown along the [0 0 1] direction, and assembled together to form an urchin-like nanostructure. Sensing performance of the sub-WO3 was investigated toward alcohol vapor. At room temperature, the sensor devices based on the WO3-x exhibit significantly higher sensitivity comparing to that of the stoichiometric WO3. The superior sensing performance of this WO3-x sensor is ascribed to the large specific surface area and abundant oxygen vacancies. The obvious enhancement of the gas sensing property can be very useful for the future design and development of room temperature gas sensors for other volatile organic compounds.

Tannic acid assisted synthesis of flake-like hydroxyapatite nanostructures at room temperature

NASA Astrophysics Data System (ADS)

Vázquez, Maricela Santana; Estevez, O.; Ascencio-Aguirre, F.; Mendoza-Cruz, R.; Bazán-Díaz, L.; Zorrila, C.; Herrera-Becerra, R.

2016-09-01

A simple and non-expensive procedure was performed to synthesize hydroxyapatite (HAp) flake-like nanostructures, by using a co-precipitation method with tannic acid as stabilizing agent at room temperature and freeze drying. Samples were synthesized with two different salts, Ca(NO3)2 and CaCl2. X-ray diffraction analysis, Raman spectroscopy, scanning and transmission electron microscopy characterizations reveal Ca10(PO4)6(OH)2 HAp particles with hexagonal structure and P63/m space group in both cases. In addition, the particle size was smaller than 20 nm. The advantage of this method over the works reported to date lies in the ease for obtaining HAp particles with a single morphology (flakes), in high yield. This opens the possibility of expanding the view to the designing of new composite materials based on the HAp synthesized at room temperature.

Realization of ground-state artificial skyrmion lattices at room temperature

DOE PAGES

Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; ...

2015-10-08

We report that the topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. We demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from themore » dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. In conclusion, the imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices.« less

Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites

PubMed Central

Araujo, C. Moyses; Nagar, Sandeep; Ramzan, Muhammad; Shukla, R.; Jayakumar, O. D.; Tyagi, A. K.; Liu, Yi-Sheng; Chen, Jeng-Lung; Glans, Per-Anders; Chang, Chinglin; Blomqvist, Andreas; Lizárraga, Raquel; Holmström, Erik; Belova, Lyubov; Guo, Jinghua; Ahuja, Rajeev; Rao, K. V.

2014-01-01

We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect. PMID:24732685

The NASA Lewis Research Center High Temperature Fatigue and Structures Laboratory

NASA Technical Reports Server (NTRS)

Mcgaw, M. A.; Bartolotta, P. A.

1987-01-01

The physical organization of the NASA Lewis Research Center High Temperature Fatigue and Structures Laboratory is described. Particular attention is given to uniaxial test systems, high cycle/low cycle testing systems, axial torsional test systems, computer system capabilities, and a laboratory addition. The proposed addition will double the floor area of the present laboratory and will be equipped with its own control room.

Bipolar resistive switching in room temperature grown disordered vanadium oxide thin-film devices

NASA Astrophysics Data System (ADS)

Wong, Franklin J.; Sriram, Tirunelveli S.; Smith, Brian R.; Ramanathan, Shriram

2013-09-01

We demonstrate bipolar switching with high OFF/ON resistance ratios (>104) in Pt/vanadium oxide/Cu structures deposited entirely at room temperature. The SET (RESET) process occurs when negative (positive) bias is applied to the top Cu electrode. The vanadium oxide (VOx) films are amorphous and close to the vanadium pentoxide stoichiometry. We also investigated Cu/VOx/W structures, reversing the position of the Cu electrode, and found the same polarity dependence with respect to the top and bottom electrodes, which suggests that the bipolar nature is linked to the VOx layer itself. Bipolar switching can be observed at 100 °C, indicating that it not due to a temperature-induced metal-insulator transition of a vanadium dioxide second phase. We discuss how ionic drift can lead to the bipolar electrical behavior of our junctions, similar to those observed in devices based on several other defective oxides. Such low-temperature processed oxide switches could be of relevance to back-end or package integration processing schemes.

Study of the structure of PyHReO{sub 4} under high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kichanov, S. E., E-mail: ekich@nf.jinr.ru; Kozlenko, D. P.; Wasicki, J. W.

2007-05-15

The structure of deuterated pyridinium perrhenate (d{sub 5}PyH)ReO{sub 4} (C{sub 5}D{sub 5}NHReO{sub 4}) is studied by X-ray diffraction at room temperature and pressures up to 3.5 GPa and by neutron diffraction in the temperature range 10-293 K and at pressures up to 2.0 GPa. Under normal conditions, this compound belongs to the orthorhombic space group Cmc2{sub 1} (ferroelectric phase II). At room temperature and pressures above P > 0.7 GPa, a transition to an orthorhombic phase (paraelectric phase II) is observed. This paraelectric phase is described by the space group Cmcm. At a pressure as high as P = 2.0more » GPa, phase I remains stable at temperatures down to 10 K. This fact indicates that the high pressure suppresses the ferroelectric state in deuterated pyridinium perrhenate (d{sub 5}PyH)ReO{sub 4}.« less

Development of High-Strength High-Temperature Cast Al-Ni-Cr Alloys Through Evolution of a Novel Composite Eutectic Structure

NASA Astrophysics Data System (ADS)

Pandey, P.; Kashyap, S.; Tiwary, C. S.; Chattopadhyay, K.

2017-12-01

Aiming to develop high-strength Al-based alloys with high material index (strength/density) for structural application, this article reports a new class of multiphase Al alloys in the Al-Ni-Cr system that possess impressive room temperature and elevated temperature (≥ 200 °C) mechanical properties. The ternary eutectic and near eutectic alloys display a complex microstructure containing intermetallic phases displaying hierarchically arranged plate and rod morphologies that exhibit extraordinary mechanical properties. The yield strengths achieved at room temperatures are in excess of 350 MPa with compressive plastic strains of more than 30 pct (without fracturing) for these alloys. The stability of the complex microstructure also leads to a yield stress of 191 ± 8 to 232 ± 5 MPa at 250 °C. It is argued that the alloys derive their high strength and impressive plasticity through synergic effects of refined nanoeutectics of two different morphologies forming a core shell type of architecture.

Single-Mode Near-Infrared Lasing in a GaAsSb-Based Nanowire Superlattice at Room Temperature

NASA Astrophysics Data System (ADS)

Ren, Dingding; Ahtapodov, Lyubomir; Nilsen, Julie S.; Yang, Jianfeng; Gustafsson, Anders; Huh, Junghwan; Conibeer, Gavin J.; van Helvoort, Antonius T. J.; Fimland, Bjørn-Ove; Weman, Helge

2018-04-01

Semiconductor nanowire lasers can produce guided coherent light emission with miniaturized geometry, bringing about new possibility for a variety of applications including nanophotonic circuits, optical sensing, and on-chip and chip-to-chip optical communications. Here, we report on the realization of single-mode room-temperature lasing from 890 nm to 990 nm utilizing a novel design of single nanowires with GaAsSb-based multiple superlattices as gain medium under optical pumping. The wavelength tunability with comprehensively enhanced lasing performance is shown to result from the unique nanowire structure with efficient gain materials, which delivers a lasing quality factor as high as 1250, a reduced lasing threshold ~ 6 kW cm-2 and a high characteristic temperature ~ 129 K. These results present a major advancement for the design and synthesis of nanowire laser structures, which can pave the way towards future nanoscale integrated optoelectronic systems with stunning performance.

Effect of Sm on dielectric, ferroelectric and piezoelectric properties of BPTNZ system

NASA Astrophysics Data System (ADS)

Kumar, Parveen; Juneja, J. K.; Prakash, Chandra; Raina, K. K.; Singh, Sangeeta

2013-10-01

Study on structural, dielectric and ferroelectric properties of Sm substituted BPTNZ system with compositional formula Ba0.80-xSmxPb0.20Zr0.10Ti0.90O3+0.5% Nb2O5 by weight, (x=0 to 0.01 in the steps of 0.0025) was done. Conventional solid state method was adopted for the synthesis of the samples. The single phase was confirmed by X-ray diffraction (XRD) analysis. Scanning electron microscopy was done for microstructural analysis. The dielectric properties were measured as a function of temperature and frequency. Ferroelectric P-E loops were recorded for all the samples at room temperature. Piezoelectric parameters such as ‘d33’ and electromechanical coupling coefficient ‘kp’ were also measured at room temperature for all the samples. The relationship between properties and structure of the prepared ceramics was established and results are discussed here.

Thermal conductivity and thermal expansion of graphite fiber/copper matrix composites

NASA Technical Reports Server (NTRS)

Ellis, David L.; Mcdanels, David L.

1991-01-01

The high specific conductivity of graphite fiber/copper matrix (Gr/Cu) composites offers great potential for high heat flux structures operating at elevated temperatures. To determine the feasibility of applying Gr/Cu composites to high heat flux structures, composite plates were fabricated using unidirectional and cross-plied pitch-based P100 graphite fibers in a pure copper matrix. Thermal conductivity of the composites was measured from room temperature to 1073 K, and thermal expansion was measured from room temperature to 1050 K. The longitudinal thermal conductivity, parallel to the fiber direction, was comparable to pure copper. The transverse thermal conductivity, normal to the fiber direction, was less than that of pure copper and decreased with increasing fiber content. The longitudinal thermal expansion decreased with increasing fiber content. The transverse thermal expansion was greater than pure copper and nearly independent of fiber content.

Thermal conductivity and thermal expansion of graphite fiber-reinforced copper matrix composites

NASA Technical Reports Server (NTRS)

Ellis, David L.; Mcdanels, David L.

1993-01-01

The high specific conductivity of graphite fiber/copper matrix (Gr/Cu) composites offers great potential for high heat flux structures operating at elevated temperatures. To determine the feasibility of applying Gr/Cu composites to high heat flux structures, composite plates were fabricated using unidirectional and cross-plied pitch-based P100 graphite fibers in a pure copper matrix. Thermal conductivity of the composites was measured from room temperature to 1073 K, and thermal expansion was measured from room temperature to 1050 K. The longitudinal thermal conductivity, parallel to the fiber direction, was comparable to pure copper. The transverse thermal conductivity, normal to the fiber direction, was less than that of pure copper and decreased with increasing fiber content. The longitudinal thermal expansion decreased with increasing fiber content. The transverse thermal expansion was greater than pure copper and nearly independent of fiber content.

Self-Propelled Hovercraft Based on Cold Leidenfrost Phenomenon

PubMed Central

Shi, Meng; Ji, Xing; Feng, Shangsheng; Yang, Qingzhen; Lu, Tian Jian; Xu, Feng

2016-01-01

The Leidenfrost phenomenon of liquid droplets levitating and dancing when placed upon a hot plate due to propulsion of evaporative vapor has been extended to many self-propelled circumstances. However, such self-propelled Leidenfrost devices commonly need a high temperature for evaporation and a structured solid substrate for directional movements. Here we observed a “cold Leidenfrost phenomenon” when placing a dry ice device on the surface of room temperature water, based on which we developed a controllable self-propelled dry ice hovercraft. Due to the sublimated vapor, the hovercraft could float on water and move in a programmable manner through designed structures. As demonstrations, we showed that the hovercraft could be used as a cargo ship or a petroleum contamination collector without consuming external power. This phenomenon enables a novel way to utilize programmable self-propelled devices on top of room temperature water, holding great potential for applications in energy, chemical engineering and biology. PMID:27338595

Self-Propelled Hovercraft Based on Cold Leidenfrost Phenomenon.

PubMed

Shi, Meng; Ji, Xing; Feng, Shangsheng; Yang, Qingzhen; Lu, Tian Jian; Xu, Feng

2016-06-24

The Leidenfrost phenomenon of liquid droplets levitating and dancing when placed upon a hot plate due to propulsion of evaporative vapor has been extended to many self-propelled circumstances. However, such self-propelled Leidenfrost devices commonly need a high temperature for evaporation and a structured solid substrate for directional movements. Here we observed a "cold Leidenfrost phenomenon" when placing a dry ice device on the surface of room temperature water, based on which we developed a controllable self-propelled dry ice hovercraft. Due to the sublimated vapor, the hovercraft could float on water and move in a programmable manner through designed structures. As demonstrations, we showed that the hovercraft could be used as a cargo ship or a petroleum contamination collector without consuming external power. This phenomenon enables a novel way to utilize programmable self-propelled devices on top of room temperature water, holding great potential for applications in energy, chemical engineering and biology.

Room temperature ferroelectricity in continuous croconic acid thin films

NASA Astrophysics Data System (ADS)

Jiang, Xuanyuan; Lu, Haidong; Yin, Yuewei; Zhang, Xiaozhe; Wang, Xiao; Yu, Le; Ahmadi, Zahra; Costa, Paulo S.; DiChiara, Anthony D.; Cheng, Xuemei; Gruverman, Alexei; Enders, Axel; Xu, Xiaoshan

2016-09-01

Ferroelectricity at room temperature has been demonstrated in nanometer-thin quasi 2D croconic acid thin films, by the polarization hysteresis loop measurements in macroscopic capacitor geometry, along with observation and manipulation of the nanoscale domain structure by piezoresponse force microscopy. The fabrication of continuous thin films of the hydrogen-bonded croconic acid was achieved by the suppression of the thermal decomposition using low evaporation temperatures in high vacuum, combined with growth conditions far from thermal equilibrium. For nominal coverages ≥20 nm, quasi 2D and polycrystalline films, with an average grain size of 50-100 nm and 3.5 nm roughness, can be obtained. Spontaneous ferroelectric domain structures of the thin films have been observed and appear to correlate with the grain patterns. The application of this solvent-free growth protocol may be a key to the development of flexible organic ferroelectric thin films for electronic applications.

J-resistance curves for Inconel 690 and Incoloy 800 nuclear steam generators tubes at room temperature and at 300 °C

NASA Astrophysics Data System (ADS)

Bergant, Marcos A.; Yawny, Alejandro A.; Perez Ipiña, Juan E.

2017-04-01

The structural integrity of steam generator tubes is a relevant issue concerning nuclear plant safety. In the present work, J-resistance curves of Inconel 690 and Incoloy 800 nuclear steam generator tubes with circumferential and longitudinal through wall cracks were obtained at room temperature and 300 °C using recently developed non-standard specimens' geometries. It was found that Incoloy 800 tubes exhibited higher J-resistance curves than Inconel 690 for both crack orientations. For both materials, circumferential cracks resulted into higher fracture resistance than longitudinal cracks, indicating a certain degree of texture anisotropy introduced by the tube fabrication process. From a practical point of view, temperature effects have found to be negligible in all cases. The results obtained in the present work provide a general framework for further application to structural integrity assessments of cracked tubes in a variety of nuclear steam generator designs.

Room temperature neutron crystallography of drug resistant HIV-1 protease uncovers limitations of X-ray structural analysis at 100K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerlits, Oksana O.; Keen, David A.; Blakeley, Matthew P.

HIV-1 protease inhibitors are crucial for treatment of HIV-1/AIDS, but their effectiveness is thwarted by rapid emergence of drug resistance. To better understand binding of clinical inhibitors to resistant HIV-1 protease, we used room-temperature joint X-ray/neutron (XN) crystallography to obtain an atomic-resolution structure of the protease triple mutant (V32I/I47V/V82I) in complex with amprenavir. The XN structure reveals a D+ ion located midway between the inner Oδ1 oxygen atoms of the catalytic aspartic acid residues. Comparison of the current XN structure with our previous XN structure of the wild-type HIV-1 protease-amprenavir complex suggests that the three mutations do not significantly altermore » the drug–enzyme interactions. This is in contrast to the observations in previous 100 K X-ray structures of these complexes that indicated loss of interactions by the drug with the triple mutant protease. These findings, thus, uncover limitations of structural analysis of drug binding using X-ray structures obtained at 100 K.« less

Room temperature neutron crystallography of drug resistant HIV-1 protease uncovers limitations of X-ray structural analysis at 100K

DOE PAGES

Gerlits, Oksana O.; Keen, David A.; Blakeley, Matthew P.; ...

2017-02-14

HIV-1 protease inhibitors are crucial for treatment of HIV-1/AIDS, but their effectiveness is thwarted by rapid emergence of drug resistance. To better understand binding of clinical inhibitors to resistant HIV-1 protease, we used room-temperature joint X-ray/neutron (XN) crystallography to obtain an atomic-resolution structure of the protease triple mutant (V32I/I47V/V82I) in complex with amprenavir. The XN structure reveals a D+ ion located midway between the inner Oδ1 oxygen atoms of the catalytic aspartic acid residues. Comparison of the current XN structure with our previous XN structure of the wild-type HIV-1 protease-amprenavir complex suggests that the three mutations do not significantly altermore » the drug–enzyme interactions. This is in contrast to the observations in previous 100 K X-ray structures of these complexes that indicated loss of interactions by the drug with the triple mutant protease. These findings, thus, uncover limitations of structural analysis of drug binding using X-ray structures obtained at 100 K.« less

Loading tests of a wing structure for a hypersonic aircraft

NASA Technical Reports Server (NTRS)

Fields, R. A.; Reardon, L. F.; Siegel, W. H.

1980-01-01

Room-temperature loading tests were conducted on a wing structure designed with a beaded panel concept for a Mach 8 hypersonic research airplane. Strain, stress, and deflection data were compared with the results of three finite-element structural analysis computer programs and with design data. The test program data were used to evaluate the structural concept and the methods of analysis used in the design. A force stiffness technique was utilized in conjunction with load conditions which produced various combinations of panel shear and compression loading to determine the failure envelope of the buckling critical beaded panels The force-stiffness data did not result in any predictions of buckling failure. It was, therefore, concluded that the panels were conservatively designed as a result of design constraints and assumptions of panel eccentricities. The analysis programs calculated strains and stresses competently. Comparisons between calculated and measured structural deflections showed good agreement. The test program offered a positive demonstration of the beaded panel concept subjected to room-temperature load conditions.

β-Na2TeO4: Phase Transition from an Orthorhombic to a Monoclinic Form. Reversible CO2 Capture.

PubMed

Galven, Cyrille; Pagnier, Thierry; Rosman, Noël; Le Berre, Françoise; Crosnier-Lopez, Marie-Pierre

2018-06-18

The present work concerns the tellurate Na 2 TeO 4 which has a 1D structure and could then present a CO 2 capture ability. It has been synthesized in a powder form via a solid-state reaction and structurally characterized by thermal X-ray diffraction experiments, Raman spectroscopy, and differential scanning calorimetry. The room temperature structure corresponds to the β-Na 2 TeO 4 orthorhombic form, and we show that it undergoes a reversible structural transition near 420 °C toward a monoclinic system. Ab initio computations were also performed on the room temperature structure, the Raman vibration modes calculated, and a normal mode attribution proposed. In agreement with our expectations, this sodium oxide is able to trap CO 2 by a two-step mechanism: Na + /H + exchange and carbonation of the released sodium as NaHCO 3 . This capture is reversible since CO 2 can be released upon heating by recombination of the mother phase.

Structure of water clusters on graphene: A classical molecular dynamics approach

NASA Astrophysics Data System (ADS)

Maekawa, Yuki; Sasaoka, Kenji; Yamamoto, Takahiro

2018-03-01

The microscopic structure of surface water adsorbed on graphene is elucidated theoretically by classical molecular dynamics simulation. At a low temperature (100 K), the main polygon consisting of hydrogen bonds in single-layered water on graphene is tetragonal, whereas the dominant polygons in double-layered water are tetragonal, pentagonal, and hexagonal. On the other hand, at room temperature, the tetragonal, pentagonal, and hexagonal water clusters are the main structures in both single- and double-layered water.

Structural, morphological and optical properties of pulsed laser deposited ZnSe/ZnSeO3 thin films

NASA Astrophysics Data System (ADS)

Hassan, Syed Ali; Bashir, Shazia; Zehra, Khushboo; Salman Ahmed, Qazi

2018-04-01

The effect of varying laser pulses on structural, morphological and optical behavior of Pulsed Laser Deposited (PLD) ZnSe/ZnSeO3 thin films has been investigated. The films were grown by employing Excimer laser (100 mJ, 248 nm, 18 ns, 30 Hz) at various number of laser pulses i.e. 3000, 4000, 5000 and 6000 with elevated substrate temperature of 300 °C. One film was grown at Room Temperature (RT) by employing 3000 number of laser pulses. In order to investigate the structural analysis of deposited films, XRD analysis was performed. It was observed that the room temperature is not favorable for the growth of crystalline film. However, elevated substrate temperature to 300°C, two phases with preferred orientation of ZnSeO3 (2 1 2) and ZnSe (3 3 1) were identified. AFM and SEM analysis were performed to explore the surface morphology of grown films. Morphological analysis also confirmed the non-uniform film growth at room temperature. At elevated substrate temperature (300 °C), the growth of dendritic rods and cubical crystalline structures are observed for lower number of laser pulses i.e. 3000 and 4000 respectively. With increased number of pulses i.e. 5000 and 6000, the films surface morphology becomes smooth which is confirmed by measurement of surface RMS roughness. Number of grains, skewness, kurtosis and other parameters have been evaluated by statistical analysis. In order to investigate the thickness, and optical properties of deposited films, ellipsometery and UV–Vis spectroscopy techniques were employed. The estimated band gap energy is 2.67 eV for the film grown at RT, whereas band gap values varies from 2.80 eV to 3.01 eV for the films grown at 300 °C with increasing number of laser pulses.

Energy-filtered cold electron transport at room temperature

PubMed Central

Bhadrachalam, Pradeep; Subramanian, Ramkumar; Ray, Vishva; Ma, Liang-Chieh; Wang, Weichao; Kim, Jiyoung; Cho, Kyeongjae; Koh, Seong Jin

2014-01-01

Fermi-Dirac electron thermal excitation is an intrinsic phenomenon that limits functionality of various electron systems. Efforts to manipulate electron thermal excitation have been successful when the entire system is cooled to cryogenic temperatures, typically <1 K. Here we show that electron thermal excitation can be effectively suppressed at room temperature, and energy-suppressed electrons, whose energy distribution corresponds to an effective electron temperature of ~45 K, can be transported throughout device components without external cooling. This is accomplished using a discrete level of a quantum well, which filters out thermally excited electrons and permits only energy-suppressed electrons to participate in electron transport. The quantum well (~2 nm of Cr2O3) is formed between source (Cr) and tunnelling barrier (SiO2) in a double-barrier-tunnelling-junction structure having a quantum dot as the central island. Cold electron transport is detected from extremely narrow differential conductance peaks in electron tunnelling through CdSe quantum dots, with full widths at half maximum of only ~15 mV at room temperature. PMID:25204839

Influence of strain rate on the structure/property behavior of the alpha-2 alloy Ti-24.5Al-10.5Nb-1.5Mo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gray, G.T. III; Hong, Sun Ig; Marquardt, B.J.

Preliminary dislocation g{center_dot}b analysis revealed that following room temperature deformation at low strain rate the majority of the dislocations are a-dislocations lying on basal planes, 2nd order pyramidal (a/2 + c) slip on [1211], and 1st order pyramidal a-slip on [1011]. Increasing the rate of deformation at room temperature to 6000 s{sup {minus}1} is seen to result in increased a-slip on prism planes and a decreased amount of basal slip. At high-strain-rates and elevated temperatures the substructure was seen to be generally similar to that observed following high-rate deformation at room temperature except for an increased amount of basal slipmore » and a somewhat higher incidence of 2nd order pyramidal slip. The defect generation and the rate sensitivity of Ti-24.5Al-10.5Nb-1.5Mo are discussed as a function of strain rate and temperature and contrasted to that observed in conventional titanium alloys and TiAl.« less

High-Temperature Modal Survey of a Hot-Structure Control Surface

NASA Technical Reports Server (NTRS)

Spivey, Natalie Dawn

2010-01-01

Ground vibration tests or modal surveys are routinely conducted for supporting flutter analysis for subsonic and supersonic vehicles; however, for hypersonic vehicle applications, thermoelastic vibration testing techniques are not well established and are not routinely performed for supporting hypersonic flutter analysis. New high-temperature material systems, fabrication technologies and high-temperature sensors expand the opportunities to develop advanced techniques for performing ground vibration tests at elevated temperatures. High-temperature materials have the unique property of increasing in stiffness when heated. When these materials are incorporated into a hot-structure, which includes metallic components that decrease in stiffness with increasing temperature, the interaction between the two materials systems needs to be understood because that interaction could ultimately affect the hypersonic flutter analysis. Performing a high-temperature modal survey will expand the research database for hypersonics and will help build upon the understanding of the dual material interaction. This paper will discuss the vibration testing of the Carbon-Silicon Carbide Ruddervator Subcomponent Test Article which is a truncated version of the full-scale X-37 hot-structure control surface. In order to define the modal characteristics of the test article during the elevated-temperature modal survey, two series of room-temperature modal test configurations had to be performed. The room-temperature test series included one with the test article suspended from a bungee cord (free-free) and the second with it mounted on the strongback (fixed boundary condition) in NASA Dryden's Flight Loads Lab large nitrogen test chamber.

Thermally actuated wedge block

DOEpatents

Queen, Jr., Charles C.

1980-01-01

This invention relates to an automatically-operating wedge block for maintaining intimate structural contact over wide temperature ranges, including cryogenic use. The wedging action depends on the relative thermal expansion of two materials having very different coefficients of thermal expansion. The wedge block expands in thickness when cooled to cryogenic temperatures and contracts in thickness when returned to room temperature.

Structural and multiferroic properties of Ba2+ doped BiFeO3 nanoparticles synthesized via sol-gel method

NASA Astrophysics Data System (ADS)

Shisode, M. V.; Kharat, Prashant B.; Bhoyar, Dhananjay N.; Vinayak, Vithal; Babrekar, M. K.; Jadhav, K. M.

2018-05-01

Ba2+ doped Bismuth ferrite nanoparticles having general formula Bi1-xBaxFeO3 (where, x = 0.00 and 0.20) were successfully synthesized by sol gel method, using nitrates as a starting material. Ethylene glycol was used as a solvent. The synthesized powder was sintered at 650°C for 4 hours to obtain pure phase BFO. Leaching with dilute nitric acid (HNO3) and distilled water (H2O) is done to remove the impurities. The structural, morphological, magnetic and ferroelectric properties were systematically investigated using standard characterization techniques like X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and room temperature magnetic behavior of the samples was studied using pulse field hysteresis loop tracer technique showing increase in saturation magnetizaion. P-E loop confirms the ferroelectric behavior of prepared nanoparticles. The coexistence of ferromagnetic and ferroelectric hysteresis loops in BFO and Bi0.8Ba0.2FeO3 nanoparticles samples at room temperature; it indicates that the samples are potential candidates for information storage and spintronics devices. The increase in magnetic properties may be important for practical application at room temperature.

Photoelectric properties of the metamorphic InAs/InGaAs quantum dot structure at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golovynskyi, S. L., E-mail: golovynskyi@isp.kiev.ua; Seravalli, L.; Trevisi, G.

We present the study of optical and photoelectric properties of InAs quantum dots (QDs) grown on a metamorphic In{sub 0.15}Ga{sub 0.85}As buffer layer: such nanostructures show efficient light emission in the telecom window at 1.3 μm (0.95 eV) at room temperature. We prepared a sample with vertical geometry of contacts isolated from the GaAs substrate. The structure is found to be photosensitive in the spectral range above 0.9 eV at room temperature, showing distinctive features in the photovoltage and photocurrent spectra attributed to QDs, InAs wetting layer, and In{sub 0.15}Ga{sub 0.85}As metamorphic buffer, while a drop in the photoelectric signal above 1.36 eV ismore » related to the GaAs layer. No effect of defect centers on the photoelectrical properties is found, although they are observed in the absorption spectrum. We conclude that metamorphic QDs have a low amount of interface-related defects close to the optically active region and charge carriers can be effectively collected into InAs QDs.« less

Kinetic parameters and structural variations in Cu-Al-Mn and Cu-Al-Mn-Mg shape memory alloys

NASA Astrophysics Data System (ADS)

Canbay, Canan Aksu

2017-02-01

In this work polycrystalline Cu-Al-Mn and Cu-Al-Mn-Mg SMAs were fabricated by arc melting. The thermal analysis was made to determine the characteristic transformation temperatures of the samples and kinetic parameters. Also the effect of Mg on transformation temperatures and kinetic parameters detected. The structural analysis was made to designate the diffraction planes of martensite phase at room temperature and this was supported by optical measurement observations.

First-principles study of lattice thermal conductivity in ZrTe5 and HfTe5

NASA Astrophysics Data System (ADS)

Wang, Cong; Wang, Haifeng; Chen, Y. B.; Yao, Shu-Hua; Zhou, Jian

2018-05-01

Recently, the layered transition-metal pentatellurides ZrTe5 and HfTe5 have attracted increasing attention because of their interesting topological electronic properties. Nevertheless, some of their other good physical properties seem to be ignored now. Actually, both ZrTe5 and HfTe5 have high electric conductivities (>105 Ω-1 m-1) and Seebeck coefficients (> 100 μV/K) at room temperature, thus making them promising thermoelectric materials. However, the disadvantage is that the thermal conductivities of the two materials are relatively high according to the few available experiments; meanwhile, the detailed mechanism of the intrinsic thermal conductivity has not been studied yet. Based on the density functional theory and the Boltzmann transport theory, we present here the theoretical study of the intrinsic lattice thermal conductivities of ZrTe5 and HfTe5, which are found to be in the range of 5-8 W/mṡK at room temperature and well consistent with the experimental results. We also find that the thermal conductivities of the two materials are anisotropic, which are mainly caused by their anisotropic crystal structures. Based on the detailed analysis, we proposed that the thermal conductivities of the two materials could possibly be reduced by different kinds of structural engineering at the atomic and mesoscopic scales, such as alloying, doping, nano-structuring, and polycrystalline structuring, which could make ZrTe5 and HfTe5 good thermoelectric materials for room temperature thermoelectric applications.

Changes in the Coherent Dynamics of Nanoconfined Room Temperature Ionic Liquids

NASA Astrophysics Data System (ADS)

Vallejo, Kevin; Cano, Melissa; Li, Song; Rotner, Gernot; Faraone, Antonio; Banuelos, Jose

Confinement and temperature effects on the coherent dynamics of the room temperature ionic liquid (RTIL) [C10MPy+] [Tf2N-] were investigated using neutron spin-echo (NSE) in two silica matrices with different pore size. Several intermolecular forces give rise to the bulk molecular structure between anions and cations. NSE provided dynamics (via the coherent intermediate scattering function) in the time range of 0.004 to 10 ns, and at Q-values corresponding to intermediate range ordering and inter- and intra-molecular length scales of the RTIL. Pore wall effects were delineated by comparing bulk RTIL dynamics with those of the confined fluid in 2.8 nm and 8 nm pores. Analytical models were applied to the experimental data to extract decay times and amplitudes of each component. We find a fast relaxation outside the experiment time window, a primary relaxation, and slow, surface-induced dynamics, which all speed up with increased temperature, however, the temperature dependence differs between bulk and confinement. This study sheds light on the structure and dynamics of RTILs and is relevant to the optimization of RTILs for green technologies and applications.

Driving Curie temperature towards room temperature in the half-metallic ferromagnet K2Cr8O16 by soft redox chemistry.

PubMed

Pirrotta, I; Fernández-Sanjulián, J; Moran, E; Alario-Franco, M A; Gonzalo, E; Kuhn, A; García-Alvarado, F

2012-02-14

The half-metallic ferromagnet K(2)Cr(8)O(16) with the hollandite structure has been chemically modified using soft chemistry methods to increase the average oxidation state of chromium. The synthesis of the parent material has been performed under high pressure/high temperature conditions. Following this, different redox reactions have been carried out on K(2)Cr(8)O(16). Oxidation to obtain potassium-de-inserted derivatives, K(2-x)Cr(8)O(16) (0 ≤x≤ 1), has been investigated with electrochemical methods, while the synthesis of sizeable amounts was achieved chemically by using nitrosonium tetrafluoroborate as a highly oxidizing agent. The maximum amount of extracted K ions corresponds to x = 0.8. Upon oxidation the hollandite structure is maintained and the products keep high crystallinity. The de-insertion of potassium changes the Cr(3+)/Cr(4+) ratio, and therefore the magnetic properties. Interestingly, the Curie temperature increases from ca. 175 K to 250 K, getting therefore closer to room temperature.

Engineering helimagnetism in MnSi thin films

NASA Astrophysics Data System (ADS)

Zhang, S. L.; Chalasani, R.; Baker, A. A.; Steinke, N.-J.; Figueroa, A. I.; Kohn, A.; van der Laan, G.; Hesjedal, T.

2016-01-01

Magnetic skyrmion materials have the great advantage of a robust topological magnetic structure, which makes them stable against the superparamagnetic effect and therefore a candidate for the next-generation of spintronic memory devices. Bulk MnSi, with an ordering temperature of 29.5 K, is a typical skyrmion system with a propagation vector periodicity of ˜18 nm. One crucial prerequisite for any kind of application, however, is the observation and precise control of skyrmions in thin films at room-temperature. Strain in epitaxial MnSi thin films is known to raise the transition temperature to 43 K. Here we show, using magnetometry and x-ray spectroscopy, that the transition temperature can be raised further through proximity coupling to a ferromagnetic layer. Similarly, the external field required to stabilize the helimagnetic phase is lowered. Transmission electron microscopy with element-sensitive detection is used to explore the structural origin of ferromagnetism in these Mn-doped substrates. Our work suggests that an artificial pinning layer, not limited to the MnSi/Si system, may enable room temperature, zero-field skyrmion thin-film systems, thereby opening the door to device applications.

Dynamic and structural properties of room-temperature ionic liquids near silica and carbon surfaces.

PubMed

Li, Song; Han, Kee Sung; Feng, Guang; Hagaman, Edward W; Vlcek, Lukas; Cummings, Peter T

2013-08-06

The dynamic and structural properties of a room-temperature ionic liquid (RTIL) 1-butyl-3-methyl-imidazolium(trifluoromethanesulfonimide) ([C4mim][Tf2N]) confined in silica and carbon mesopores were investigated by molecular dynamics (MD) simulations and nuclear magnetic resonance (NMR) experiments. The complex interfacial microstructures of confined [C4mim][Tf2N] are attributed to the distinctive surface features of the silica mesopore. The temperature-dependent diffusion coefficients of [C4mim][Tf2N] confined in the silica or carbon mesopore exhibit divergent behavior. The loading fraction (f = 1.0, 0.5, and 0.25) has a large effect on the magnitude of the diffusion coefficient in the silica pore and displays weaker temperature dependence as the loading fraction decreases. The diffusion coefficients of mesoporous carbon-confined [C4mim][Tf2N] are relatively insensitive to the loading faction and exhibit a temperature dependence that is similar to the bulk dependence at all loading levels. Such phenomena can be attributed to the unique surface heterogeneity, dissimilar interfacial microstructures, and interaction potential profile of RTILs near silica and carbon walls.

Photoluminescence studies of a perceived white light emission from a monolithic InGaN/GaN quantum well structure

PubMed Central

Ben Sedrine, N.; Esteves, T. C.; Rodrigues, J.; Rino, L.; Correia, M. R.; Sequeira, M. C.; Neves, A. J.; Alves, E.; Bockowski, M.; Edwards, P. R.; O’Donnell, K. P.; Lorenz, K.; Monteiro, T.

2015-01-01

In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealing at 1000 °C. The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260–4000 K. PMID:26336921

Room temperature crack growth rates and -20 deg F fracture toughness of welded 1 1/4 inch A-285 steel plate

NASA Technical Reports Server (NTRS)

Shannon, J. L., Jr.; Rzasnicki, W.

1977-01-01

Data are presented which were developed in support of a structural assessment of NASA-LEWIS' 10-foot by 10-foot supersonic wind tunnel, critical portions of which are fabricated from rolled and welded 1 1/4 inch thick A-285 steel plate. Test material was flame cut from the tunnel wall and included longitudinal and circumferential weld joints. Parent metal, welds, and weld heat affected zone were tested. Tensile strength and fracture toughness were determined at -20 F, the estimated lowest tunnel operating temperature. Crack growth rates were measured at room temperature, where growth rates in service are expected to be highest.

Mechanical properties of amorphous and devitrified Ni-Zr alloy thin films: A cyclic nanoindentation study

NASA Astrophysics Data System (ADS)

Bhattacharya, Debarati; Chatterjee, Arnomitra; Jana, Swapan

2018-04-01

Thin films of Ni-Zr glassy alloy were deposited at room temperature by magnetron co-sputtering. The alloy films were vacuum annealed in steps of 200°C from room temperature up to 800 °C, where devitrification finally occurred. Mechanical properties of the films were measured after each thermal anneal, through (cyclic) nanoindentation technique. The hardness values were observed to steadily increase with annealing temperature, as the alloy films underwent an amorphous to crystalline transformation. Grazing incidence X-ray diffraction measurements were performed on the as-deposited and annealed films both before and after nanoindentation. The resistance to plastic deformation was strongly linked to the (nano)structure of the material.

[Studies on the health standard for room temperature in cold regions].

PubMed

Meng, Z L

1990-03-01

The microclimate of 205 rooms of single storey houses in four new rural residential districts in coastal and inland Shandong was monitored and studied the blood circulation of the finger, skin temperature, sweating function and other physiological indexes among 2,401 peasants. We interrogated their personal sensation to cold and warmth. The count was done by the application of thermal equilibrium index (TEI), predicted 4-hour Sweat Rate (P4SR) and the uncomfortable index. The standard room temperature is recommended as follows. In rural area in winter the appropriate room temperature is 14-16 degrees C, the comfortable room temperature is 16-20 degrees C, the lowest room temperature must not be below 14 degrees C. In summer the appropriate room temperature is 25-28 degrees C, the comfortable room temperature is 26-27 degrees C, the highest temperature must not be above 28 degrees C.

Native phasing of x-ray free-electron laser data for a G protein-coupled receptor.

PubMed

Batyuk, Alexander; Galli, Lorenzo; Ishchenko, Andrii; Han, Gye Won; Gati, Cornelius; Popov, Petr A; Lee, Ming-Yue; Stauch, Benjamin; White, Thomas A; Barty, Anton; Aquila, Andrew; Hunter, Mark S; Liang, Mengning; Boutet, Sébastien; Pu, Mengchen; Liu, Zhi-Jie; Nelson, Garrett; James, Daniel; Li, Chufeng; Zhao, Yun; Spence, John C H; Liu, Wei; Fromme, Petra; Katritch, Vsevolod; Weierstall, Uwe; Stevens, Raymond C; Cherezov, Vadim

2016-09-01

Serial femtosecond crystallography (SFX) takes advantage of extremely bright and ultrashort pulses produced by x-ray free-electron lasers (XFELs), allowing for the collection of high-resolution diffraction intensities from micrometer-sized crystals at room temperature with minimal radiation damage, using the principle of "diffraction-before-destruction." However, de novo structure factor phase determination using XFELs has been difficult so far. We demonstrate the ability to solve the crystallographic phase problem for SFX data collected with an XFEL using the anomalous signal from native sulfur atoms, leading to a bias-free room temperature structure of the human A 2A adenosine receptor at 1.9 Å resolution. The advancement was made possible by recent improvements in SFX data analysis and the design of injectors and delivery media for streaming hydrated microcrystals. This general method should accelerate structural studies of novel difficult-to-crystallize macromolecules and their complexes.

Structural and Mössbauer analysis of pure and Ce-Dy doped cobalt ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Hashim, Mohd.; Meena, Sher Singh; Kumar, Shalendra; Ahmed, Ateeq; Bhatt, Pramod

2018-05-01

Ce and Dy doped Cobalt ferrites with the chemical composition CoCexDyxFe2-2xO4 (x = 0.00 and 0.04) were synthesized via the chemical route using citrate-gel auto-combustion method. The structural analysis has been carried out with the help of x-ray diffraction (XRD). Formation of spinel cubic structure of the ferrites was confirmed by XRD analysis. Mössbauer spectra were recorded for both samples at room temperature. Presence of the well resolved sextet spectra corresponding to A and B sub-lattice clearly shows that both the samples have ferrimagnetic ordering at room temperature. Isomer shift observed from fitting of the Mössbauer spectra infers that Fe3+ ions are in high valence state. The decrease in the hyperfine field due to the doping of Ce and Dy clearly showed that magnetic interactions diluted due to the doping of Ce and Dy ions.

Room temperature synthesis of Cu₂O nanospheres: optical properties and thermal behavior.

PubMed

Nunes, Daniela; Santos, Lídia; Duarte, Paulo; Pimentel, Ana; Pinto, Joana V; Barquinha, Pedro; Carvalho, Patrícia A; Fortunato, Elvira; Martins, Rodrigo

2015-02-01

The present work reports a simple and easy wet chemistry synthesis of cuprous oxide (Cu2O) nanospheres at room temperature without surfactants and using different precursors. Structural characterization was carried out by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy coupled with focused ion beam and energy-dispersive X-ray spectroscopy. The optical band gaps were determined from diffuse reflectance spectroscopy. The photoluminescence behavior of the as-synthesized nanospheres showed significant differences depending on the precursors used. The Cu2O nanospheres were constituted by aggregates of nanocrystals, in which an on/off emission behavior of each individual nanocrystal was identified during transmission electron microscopy observations. The thermal behavior of the Cu2O nanospheres was investigated with in situ X-ray diffraction and differential scanning calorimetry experiments. Remarkable structural differences were observed for the nanospheres annealed in air, which turned into hollow spherical structures surrounded by outsized nanocrystals.

Crystalline Structure, Defect Chemistry and Room Temperature Colossal Permittivity of Nd-doped Barium Titanate

NASA Astrophysics Data System (ADS)

Sun, Qiaomei; Gu, Qilin; Zhu, Kongjun; Jin, Rongying; Liu, Jinsong; Wang, Jing; Qiu, Jinhao

2017-02-01

Dielectric materials with high permittivity are strongly demanded for various technological applications. While polarization inherently exists in ferroelectric barium titanate (BaTiO3), its high permittivity can only be achieved by chemical and/or structural modification. Here, we report the room-temperature colossal permittivity (~760,000) obtained in xNd: BaTiO3 (x = 0.5 mol%) ceramics derived from the counterpart nanoparticles followed by conventional pressureless sintering process. Through the systematic analysis of chemical composition, crystalline structure and defect chemistry, the substitution mechanism involving the occupation of Nd3+ in Ba2+ -site associated with the generation of Ba vacancies and oxygen vacancies for charge compensation has been firstly demonstrated. The present study serves as a precedent and fundamental step toward further improvement of the permittivity of BaTiO3-based ceramics.

Crystalline Structure, Defect Chemistry and Room Temperature Colossal Permittivity of Nd-doped Barium Titanate.

PubMed

Sun, Qiaomei; Gu, Qilin; Zhu, Kongjun; Jin, Rongying; Liu, Jinsong; Wang, Jing; Qiu, Jinhao

2017-02-13

Dielectric materials with high permittivity are strongly demanded for various technological applications. While polarization inherently exists in ferroelectric barium titanate (BaTiO 3 ), its high permittivity can only be achieved by chemical and/or structural modification. Here, we report the room-temperature colossal permittivity (~760,000) obtained in xNd: BaTiO 3 (x = 0.5 mol%) ceramics derived from the counterpart nanoparticles followed by conventional pressureless sintering process. Through the systematic analysis of chemical composition, crystalline structure and defect chemistry, the substitution mechanism involving the occupation of Nd 3+ in Ba 2+ -site associated with the generation of Ba vacancies and oxygen vacancies for charge compensation has been firstly demonstrated. The present study serves as a precedent and fundamental step toward further improvement of the permittivity of BaTiO 3 -based ceramics.

Effect of Cr doping on structural and magnetic properties of ZnS nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Virpal,; Singh, Jasvir; Sharma, Sandeep

2016-05-23

The structural, optical and magnetic properties of pure and Cr doped ZnS nanoparticles were studied at room temperature. X-ray diffraction analysis confirmed the absence of any mixed phase and the cubic structure of ZnS in pure and Cr doped ZnS nanoparticles. Fourier transfer infrared spectra confirmed the Zn-S stretching bond at 664 cm{sup −1} of ZnS in all prepared nanoparticles. The UV-Visible absorption spectra showed blue shift which became even more pronounced in Cr doped ZnS nanoparticles. However, at relatively higher Cr concentrations a slower red shift was shown by the doped nanoparticles. This phenomenon is attributed to sp-d exchange interactionmore » that becomes prevalent at higher doping concentrations. Further, magnetic hysteresis measurements showed that Cr doped ZnS nanoparticles exhibited ferromagnetic behavior at room temperature.« less

Structural and magnetic properties of nanocrystalline NiFe2O4 thin film prepared by spray pyrolysis technique

NASA Astrophysics Data System (ADS)

Chavan, Apparao R.; Chilwar, R. R.; Shisode, M. V.; Hivrekar, Mahesh M.; Mande, V. K.; Jadhav, K. M.

2018-05-01

The nanocrystalline NiFe2O4 thin film has been prepared using a spray pyrolysis technique on glass substrate. The prepared thin film was characterized by using X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR), and Field Emission-Scanning Electron Microscopy (FE-SEM) characterization techniques for the structural and microstructural analysis. The magnetic property was measured using vibrating sample magnetometer (VSM) at room temperature. X-ray diffraction studies show the formation of single phase spinel structure of the thin film. The octahedral and tetrahedral vibration in the sample was studied by Fourier transform infrared (FT-IR) spectra. Magnetic hysteresis loop was recorded for thin film at room temperature. At 15 kOe, saturation magnetization (Ms) was found to increase while coercivity (Hc) decreases with thickness of the NiFe2O4 thin film.

Crystalline Structure, Defect Chemistry and Room Temperature Colossal Permittivity of Nd-doped Barium Titanate

PubMed Central

Sun, Qiaomei; Gu, Qilin; Zhu, Kongjun; Jin, Rongying; Liu, Jinsong; Wang, Jing; Qiu, Jinhao

2017-01-01

Dielectric materials with high permittivity are strongly demanded for various technological applications. While polarization inherently exists in ferroelectric barium titanate (BaTiO3), its high permittivity can only be achieved by chemical and/or structural modification. Here, we report the room-temperature colossal permittivity (~760,000) obtained in xNd: BaTiO3 (x = 0.5 mol%) ceramics derived from the counterpart nanoparticles followed by conventional pressureless sintering process. Through the systematic analysis of chemical composition, crystalline structure and defect chemistry, the substitution mechanism involving the occupation of Nd3+ in Ba2+ -site associated with the generation of Ba vacancies and oxygen vacancies for charge compensation has been firstly demonstrated. The present study serves as a precedent and fundamental step toward further improvement of the permittivity of BaTiO3-based ceramics. PMID:28205559

Room temperature electroluminescence from the n-ZnO/p-GaN heterojunction device grown by MOCVD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, T.P.; Zhu, H.C.; Bian, J.M.

2008-12-01

The heterojunction light-emitting diode with n-ZnO/p-GaN structure was grown on (0 0 0 1) sapphire substrate by metalorganic chemical vapor deposition (MOCVD) technique. The heterojunction structure was consisted of an Mg-doped p-type GaN layer with a hole concentration of {approx}10{sup 17} cm{sup -3} and a unintentionally doped n-type ZnO layer with an electron concentration of {approx}10{sup 18} cm{sup -3}. A distinct blue-violet electroluminescence with a dominant emission peak centered at {approx}415 nm was observed at room temperature from the heterojunction structure under forward bias conditions. The origins of the electroluminescence (EL) emissions are discussed in comparison with the photoluminescence spectra,more » and it was supposed to be attributed to a radiative recombination in both n-ZnO and p-GaN sides.« less

Emissivity measurement of coated copper and aluminum samples at 80 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, S. H.; Conway, Z. A.; Ostroumov, P. N.

Accelerator cryomodules reduce the radiative thermal load to the 1.8 – 4.5 K components by enclosing them within low-emissivity shields cooled to 70–100 K. These heat shields are not continuous and have many penetrations, or holes, to allow for the connection of support structures and the many subsystems running from room temperature. The penetrations have thermal baffles to reduce, or eliminate if possible, the direct line-of-sight between room temperature and the lower temperature components but leave many, low emissivity, paths with only a single reflection required for the room temperature photons to strike the 1.8 – 4.5 K surfaces. Tomore » reduce this we are coating our baffles such that the surfaces which face lower temperatures have a low-emissivity while the surfaces which the photons may reflect from but do not have line-of-sight to lower temperature surfaces have a high-absorption. We measure emissivities of different coatings from the heat balance between absorption, from background radiation and the heater attached on the sample, and emission powers. In this paper, design details of our experiment and measurement results will be presented.« less

The crystal structure of lueshite at 298 K resolved by high-resolution time-of-flight neutron powder diffraction

NASA Astrophysics Data System (ADS)

Mitchell, Roger H.; Kennedy, Brendan J.; Knight, Kevin S.

2018-01-01

Refinement of time-of-flight high-resolution neutron powder diffraction data for lueshite (Na, Ca)(Nb, Ta, Ti)O3, the natural analogue of synthetic NaNbO3, demonstrates that lueshite at room temperature (298 K) adopts an orthorhombic structure with a 2 a p × 2 a p × 4 a p superlattice described by space group Pmmn [#59: a = 7.8032(4) Å; b = 7.8193(4) Å; c = 15.6156(9) Å]. This structure is analogous to that of phase S of synthetic NaNbO3 observed at 753-783 K (480-510 °C). In common with synthetic NaNbO3, lueshite exhibits a series of phase transitions with decreasing temperature from a cubic (Pm\\bar{3}m) aristotype through tetragonal ( P4/ mbm) and orthorhombic ( Cmcm) structures. However, the further sequence of phase transitions differs in that for lueshite the series terminates with the room temperature S ( Pmmn) phase, and the R ( Pmmn or Pnma) and P ( Pbcm) phases of NaNbO3 are not observed. The appearance of the S phase in lueshite at a lower temperature, relative to that of NaNbO3, is attributable to the effects of solid solution of Ti, Ta and Ca in lueshite.

Polymer-stabilized liquid crystal blue phases.

PubMed

Kikuchi, Hirotsugu; Yokota, Masayuki; Hisakado, Yoshiaki; Yang, Huai; Kajiyama, Tisato

2002-09-01

Blue phases are types of liquid crystal phases that appear in a temperature range between a chiral nematic phase and an isotropic liquid phase. Because blue phases have a three-dimensional cubic structure with lattice periods of several hundred nanometres, they exhibit selective Bragg reflections in the range of visible light corresponding to the cubic lattice. From the viewpoint of applications, although blue phases are of interest for fast light modulators or tunable photonic crystals, the very narrow temperature range, usually less than a few kelvin, within which blue phases exist has always been a problem. Here we show the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260-326 K). Furthermore, we demonstrate an electro-optical switching with a response time of the order of 10(-4) s for the stabilized blue phases at room temperature.

Room-temperature Electrochemical Synthesis of Carbide-derived Carbons and Related Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gogotsi, Yury

2015-02-28

This project addresses room-temperature electrochemical etching as an energy-efficient route to synthesis of 3D nanoporous carbon networks and layered 2D carbons and related structures, as well as provides fundamental understanding of structure and properties of materials produced by this method. Carbide-derived-carbons (CDCs) are a growing class of nanostructured carbon materials with properties that are desirable for many applications, such as electrical energy and gas storage. The structure of these functional materials is tunable by the choice of the starting carbide precursor, synthesis method, and process parameters. Moving from high-temperature synthesis of CDCs through vacuum decomposition above 1400°C and chlorination abovemore » 400°C, our studies under the previous DOE BES support led to identification of precursor materials and processing conditions for CDC synthesis at temperatures as low as 200°C, resulting in amorphous and highly reactive porous carbons. We also investigated synthesis of monolithic CDC films from carbide films at 250-1200°C. The results of our early studies provided new insights into CDC formation, led to development of materials for capacitive energy storage, and enabled fundamental understanding of the electrolyte ions confinement in nanoporous carbons.« less

Evolution of the Structure of Cu-1% Sn Bronze under High Pressure Torsion and Subsequent Annealing

NASA Astrophysics Data System (ADS)

Popov, V. V.; Popova, E. N.; Stolbovsky, A. V.; Falahutdinov, R. M.

2018-04-01

The evolution of the structure of tin bronze under the room-temperature high-pressure torsion with different degrees of deformation and the subsequent annealing has been investigated. The thermal stability of the structure formed, namely, its behavior upon annealing in the temperature range of 150-400°C has been studied. The possibility of alloying copper with tin has been analyzed with the purpose of obtaining a thermally stable nanostructure with high strength characteristics.

Heat capacity and magnetic properties of fluoride CsFe{sup 2+}Fe{sup 3+}F{sub 6} with defect pyrochlore structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gorev, M.V., E-mail: gorev@iph.krasn.ru; Institute of Engineering Physics and Radio Electronics, Siberian State University, 660074 Krasnoyarsk; Flerov, I.N.

2016-05-15

Heat capacity, Mössbauer and Raman spectra as well as magnetic properties of fluoride CsFe{sub 2}F{sub 6} with defect pyrochlore structure were studied. In addition to recently found above room temperature three successive structural transformations Pnma-Imma-I4{sub 1}amd-Fd-3m, phase transition of antiferromagnetic nature with the 13.7 K Neel temperature and a broad heat capacity anomaly with a maximum at about 30 K were observed. The room temperature symmetry Pnma is unchanged at least down to 7 K. Simple model of indirect bond used to estimate the exchange interactions and to propose a magnetic structure model. - Graphical abstract: The ordered arrangement ofmore » Fe{sup 2+} and Fe{sup 3+} ions in high-spin states as well as antiferromagnetic phase transition followed by significant magnetic frustrations were found in pyrocholore-related CsFe{sup 2+}Fe{sup 3+}F{sub 6}. A magnetic structure was proposed using a simple model of indirect bonds. - Highlights: • The Pnma structure in pyrocholore CsFe{sub 2}F{sub 6} is stable down to helium temperature. • Mössbauer spectra confirmed the ordering of Fe{sup 2+} and Fe{sup 3+} ions. • Antiferromagnetic transformation and significant magnetic frustrations are found. • Experimental magnetic entropy agrees with entropy for Fe ions in high-spin state. • Superexchange interactions were calculated and a magnetic structure was proposed.« less

Facile fabrication of high-performance InGaZnO thin film transistor using hydrogen ion irradiation at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, Byung Du; Park, Jin-Seong; Chung, K. B., E-mail: kbchung@dongguk.edu

Device performance of InGaZnO (IGZO) thin film transistors (TFTs) are investigated as a function of hydrogen ion irradiation dose at room temperature. Field effect mobility is enhanced, and subthreshold gate swing is improved with the increase of hydrogen ion irradiation dose, and there is no thermal annealing. The electrical device performance is correlated with the electronic structure of IGZO films, such as chemical bonding states, features of the conduction band, and band edge states below the conduction band. The decrease of oxygen deficient bonding and the changes in electronic structure of the conduction band leads to the improvement of devicemore » performance in IGZO TFT with an increase of the hydrogen ion irradiation dose.« less

Atomistic structures of nano-engineered SiC and radiation-induced amorphization resistance

DOE PAGES

Imada, Kenta; Ishimaru, Manabu; Sato, Kazuhisa; ...

2015-06-18

In this paper, nano-engineered 3C–SiC thin films, which possess columnar structures with high-density stacking faults and twins, were irradiated with 2 MeV Si ions at cryogenic and room temperatures. From cross-sectional transmission electron microscopy observations in combination with Monte Carlo simulations based on the Stopping and Range of Ions in Matter code, it was found that their amorphization resistance is six times greater than bulk crystalline SiC at room temperature. High-angle bright-field images taken by spherical aberration corrected scanning transmission electron microscopy revealed that the distortion of atomic configurations is localized near the stacking faults. Finally, the resultant strain fieldmore » probably contributes to the enhancement of radiation tolerance of this material.« less

Sealed head access area enclosure

DOEpatents

Golden, Martin P.; Govi, Aldo R.

1978-01-01

A liquid-metal-cooled fast breeder power reactor is provided with a sealed head access area enclosure disposed above the reactor vessel head consisting of a plurality of prefabricated structural panels including a center panel removably sealed into position with inflatable seals, and outer panels sealed into position with semipermanent sealant joints. The sealant joints are located in the joint between the edge of the panels and the reactor containment structure and include from bottom to top an inverted U-shaped strip, a lower layer of a room temperature vulcanizing material, a separator strip defining a test space therewithin, and an upper layer of a room temperature vulcanizing material. The test space is tapped by a normally plugged passage extending to the top of the enclosure for testing the seal or introducing a buffer gas thereinto.

Structural, optical and magnetic behaviour of nanocrystalline Volborthite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arvind, Hemant K., E-mail: hemantarvind@gmail.com; Kumar, Sudhish, E-mail: skmlsu@gmail.com; Kalal, Sangeeta

2016-05-06

Nanocrystalline sample of Volborthite (Copper Pyrovanadate: Cu{sub 3}V{sub 2} (OH){sub 2}O{sub 7}.2H{sub 2}O) has been synthesized using wet chemical route and characterized by XRD, SEM, FTIR, UV-Vis-NIR spectroscopic and magnetization measurements. Room temperature X-ray diffraction analysis confirms the single phase monoclinic structure and nanocrystalline nature of Volborthite. The UV-Visible optical absorption spectrum displays two broad absorption peaks in the range of 200-350 nm and 400-1000 nm. The direct band gap is found to be E{sub g}= ∼2.74 eV. Bulk Volborthite was reported to be a natural frustrated antiferromagnet, however our nanocrystalline Volborthite display week ferromagnetic hysteresis loop with very small coercivity andmore » retentivity at room temperature.« less

Near room temperature and large-area synthesis of ZnO/Cu2O heterojunction for photocatalytic properties

NASA Astrophysics Data System (ADS)

Gao, Shiyong; Zhang, Jiejing; Li, Wenqiang; Jiao, Shujie; Nie, Yanguang; Fan, Huaiyun; Zeng, Zhi; Yu, Qingjiang; Wang, Jinzhong; Zhang, Xitian

2018-01-01

Large-area ZnO/Cu2O heterojunction have been successfully synthesized on Cu foil through a simple two-step solution method at near room temperature. The field emission scanning electron microscopy characterization indicates that the morphology of as-prepared Cu2O film grown on Cu foil is octahedral structure with diameter of ∼450 nm and ZnO is nanorod arrays structure with diameter of ∼150 nm. The current-voltage measurement of ZnO/Cu2O heterojunction shows a typical rectifying characteristics. Moreover, the photocatalytic test indicates that ZnO/Cu2O heterojunction exhibits high photocatalytic efficient for degradation of congo red dyes. The possible photocatalytic mechanism of ZnO/Cu2O heterojunction is also presented.

Correlation of microstructure and thermo-mechanical properties of a novel hydrogen transport membrane

NASA Astrophysics Data System (ADS)

Zhang, Yongjun

A key part of the FutureGen concept is to support the production of hydrogen to fuel a "hydrogen economy," with the use of clean burning hydrogen in power-producing fuel cells, as well as for use as a transportation fuel. One of the key technical barriers to FutureGen deployment is reliable and efficient hydrogen separation technology. Most Hydrogen Transport Membrane (HTM) research currently focuses on separation technology and hydrogen flux characterization. No significant work has been performed on thermo-mechanical properties of HTMs. The objective of the thesis is to understand the structure-property correlation of HTM and to characterize (1) thermo mechanical properties under different reducing environments and thermal cycles (thermal shock), and (2) evaluate the stability of the novel HTM material. A novel HTM cermet bulk sample was characterized for its physical and mechanical properties at both room temperature and at elevated temperature up to 1000°C. Micro-structural properties and residual stresses were evaluated in order to understand the changing mechanism of the microstructure and its effects on the mechanical properties of materials. A correlation of the microstructural and thermo mechanical properties of the HTM system was established for both HTM and the substrate material. Mechanical properties of both selected structural ceramics and the novel HTM cermet bulk sample are affected mainly by porosity and microstructural features, such as grain size and pore size-distribution. The Young's Modulus (E-value) is positively correlated to the flexural strength for materials with similar crystallographic structure. However, for different crystallographic materials, physical properties are independent of mechanical properties. Microstructural properties, particularly, grain size and crystallographic structure, and thermodynamic properties are the main factors affecting the mechanical properties at both room and high temperatures. The HTM cermet behaves more like an elastic material at room temperature and as a ductile material at temperature above 850°C. The oxidation and the plasticity of Pd phase mainly affected the mechanical properties of HTM cermet at high temperature, also as a result of thermal cycling. Residual stress induced in the HTM by thermo cycles also plays a very critical role in defining the thermo-mechanical properties.

Composite Structure Repair. Addendum

DTIC Science & Technology

1984-08-01

room temperature curing systems . For permanent repairs no reduction in " serciveability with regard to the maximum design temperature and the design...pressure for ply compaction and conformation of bonding surfaces. In certain instances, ambient temperature cure systems may be sufficient. - Noisture...than those placed on radomes. Some of ,the resins used for the repairs were ambient curing systems which also required no additional pressure for

Wurtzite Spin-Lasers

NASA Astrophysics Data System (ADS)

Xu, Gaofeng; Faria Junior, Paulo E.; Sipahi, Guilherme M.; Zutic, Igor

Lasers in which spin-polarized carriers are injected provide paths to different practical room temperature spintronic devices, not limited to magnetoresistive effects. While theoretical studies of such spin-lasers have focused on zinc-blende semiconductors as their active regions, the first electrically injected carriers at room temperature were recently demonstrated in GaN-based wurtzite semiconductors, recognized also for the key role as highly-efficient light emitting diodes. By focusing on a wurtzite quantum well-based spin-laser, we use accurate electronic structure calculations to develop a microscopic description for its lasing properties. We discuss important differences between wurtzite and zinc-blende spin-lasers.

Conductance bistability of gold nanowires at room temperature

NASA Astrophysics Data System (ADS)

Kiguchi, Manabu; Konishi, Tatsuya; Murakoshi, Kei

2006-03-01

Quantized conductance behavior of gold nanowires was studied under electrochemical potential control. We fabricated 1-nm -long monoatomic wires in solution at room temperature. Electrochemical potential significantly affected the stability of the monoatomic wire and fractional conductance peak occurrence in the conductance histogram. We revealed that the hydrogen adsorption on gold monoatomic wires was a decisive factor of the fractional peak, which was originated from the dynamic structural transition between two bistable states of the monoatomic wire showing the unit and the fractional values of the conductance. We could tune the stability of these bistable states to make the fractional conductance state preferable.

Room-temperature transition-metal-free one-pot synthesis of 3-aryl imidazo[1,2-a]pyridines via iodo-hemiaminal intermediate.

PubMed

Lee, Seul Ki; Park, Jin Kyoon

2015-04-03

A mild and efficient one-pot synthesis of 3-aryl imidazo[1,2-a]pyridines in up to 88% yield was developed. An adduct was formed after the simple mixing of 2-amino-4-methylpyridine, 2-phenylacetaldehyde, and N-iodosuccinimide in CH2Cl2, and the structure of the adduct was characterized by 2D NMR, IR, and high-resolution mass analysis. The adduct was readily cyclized by treatment with a saturated aqueous solution of NaHCO3. The reactions proceeded to completion after several hours at room temperature.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oda, H., E-mail: h-oda@photon.chitose.ac.jp; Yamanaka, A.; Ozaki, N.

The development of small sized laser operating above room temperature is important in the realization of optical integrated circuits. Recently, micro-lasers consisting of photonic crystals (PhCs) and whispering gallery mode cavities have been demonstrated. Optically pumped laser devices could be easily designed using photonic crystal-slab waveguides (PhC-WGs) with an air-bridge type structure. In this study, we observe lasing at 1.3μm from two-photon pumped InAs-quantum-dots embedded GaAs PhC-WGs above room temperature. This type of compact laser shows promise as a new light source in ultra-compact photonics integrated circuits.

GaSbBi/GaSb quantum well laser diodes

NASA Astrophysics Data System (ADS)

Delorme, O.; Cerutti, L.; Luna, E.; Narcy, G.; Trampert, A.; Tournié, E.; Rodriguez, J.-B.

2017-05-01

We report on the structural and optical properties of GaSbBi single layers and GaSbBi/GaSb quantum well heterostructures grown by molecular beam epitaxy on GaSb substrates. Excellent crystal quality and room-temperature photoluminescence are achieved in both cases. We demonstrate laser operation from laser diodes with an active zone composed of three GaSb0.885Bi0.115/GaSb quantum wells. These devices exhibit continuous-wave lasing at 2.5 μm at 80 K, and lasing under pulsed operation at room-temperature near 2.7 μm.

The influence of aeration and temperature on the structure of bacterial complexes in high-moor peat soil

NASA Astrophysics Data System (ADS)

Kukharenko, O. S.; Pavlova, N. S.; Dobrovol'Skaya, T. G.; Golovchenko, A. V.; Pochatkova, T. N.; Zenova, G. M.; Zvyagintsev, D. G.

2010-05-01

The number and taxonomic structure of the heterotrophic block of aerobic and facultative anaerobic bacteria were studied in monoliths from a high-moor peat (stored at room temperature and in a refrigerator) and in the peat horizons mixed in laboratory vessels. The monitoring lasted for a year. In the T0 horizon, spirilla predominated at room and low temperatures; in the T1 and T2 horizons, bacilli were the dominants. The continuous mixing of the peat layers increased the oxygen concentration and the peat decomposition; hence, the shares of actinomycetes and bacilli (bacteria of the hydrolytic complex) increased. In the peat studied, the bacilli were in the active state; i.e., vegetative cells predominated, whose amount ranged from 65 to 90%. The representatives of the main species of bacilli (the facultative anaerobic forms prevailed) hydrolyzed starch, pectin, and carboxymethylcellulose. Thus, precisely sporiferous bacteria can actively participate in the decomposition of plant polysaccharides in high-moor peat soils that are characterized by low temperatures and an oxygen deficit. The development of actinomycetes is inhibited by low temperatures; they can develop only under elevated temperature and better aeration.

Photo-induced Low Temperature Structural Transition in the "114" YbaFe 4O 7 oxide

DOE PAGES

Duffort, V.; Caignaert, Vincent; Pralong, V.; ...

2013-11-11

Synchrotron irradiation of the oxide YBaFe 4O 7.0 below 190 K converts the low temperature monoclinic structure to a higher symmetry tetragonal form analogous to the room temperature structure. This photo-induced metastable tetragonal form is stable even in the absence of irradiation over the range 4-60 K, however, above 60 K the photo-transition is reversible. These structural phenomena are correlated to the magnetic behaviour of this system, suggesting possible spin-lattice coupling. Lastly, a scenario explaining the low temperature photo-induced transition is proposed, based on the different distributions of the valence electrons in the iron sub-lattice of the monoclinic and tetragonalmore » phases.« less

Structural, XPS and magnetic studies of pulsed laser deposited Fe doped Eu{sub 2}O{sub 3} thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Sandeep; Prakash, Ram, E-mail: rpgiuc@gmail.com; Choudhary, R.J.

2015-10-15

Highlights: • Growth of Fe doped Eu{sub 2}O{sub 3} thin films by PLD. • XRD and Raman’s spectroscopy used for structure confirmation. • The electronic states of Eu and Fe are confirmed by XPS. • Magnetic properties reveals room temperature magnetic ordering in deposited film. - Abstract: Fe (4 at.%) doped europium (III) oxide thin film was deposited on silicon (1 0 0) substrate by pulsed laser deposition technique. Structural, spectral and magnetic properties were studied by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and magnetization measurements. XRD and Raman spectroscopy reveal that the grown film is singlemore » phased and belongs to the cubic structure of Eu{sub 2}O{sub 3}. XPS study of the Eu{sub 1.92}Fe{sub 0.08}O{sub 3} film shows that Fe exists in Fe{sup 3+} ionic state in the film. The film exhibits magnetic ordering at room temperature.« less

High-pressure effects on cooking loss and histological structure of beef muscle

NASA Astrophysics Data System (ADS)

Liu, Anjun; Zhan, Hu; Zheng, Jie; Liu, Dongyue; Jia, Peiqi

2010-12-01

In this study, we investigate the effects of high pressures (up to 600 MPa) applied at room temperature for 10 min on beef cooking loss and structure. The data on cooking loss, pH and protein solubility, as well as the electron microscopy, illustrate the changes in cooking loss and structure with high pressure processing (HPP). There is a significant reduction in cooking loss of beef with HPP. When the beef sample is imposed upon by 300 or 400 MPa, the cooking loss reduction is about 12%. Further, the pH of beef is dramatically increased as the pressure increases, and the pH increases by about 5% when imposed upon by 500 MPa. When a high pressure was applied at room temperature, the structure of the beef tissue apparently changed. Muscle fiber fragments gradually became slender and sarcomeres became lengthened. Our data indicated that high-pressure treatment on beef leads to stretching of the muscle fiber and an increase in the water-holding capacity.

Reference breast temperature: proposal of an equation.

PubMed

Souza, Gladis Aparecida Galindo Reisemberger de; Brioschi, Marcos Leal; Vargas, José Viriato Coelho; Morais, Keli Cristiane Correia; Dalmaso Neto, Carlos; Neves, Eduardo Borba

2015-01-01

To develop an equation to estimate the breast reference temperature according to the variation of room and core body temperatures. Four asymptomatic women were evaluated for three consecutive menstrual cycles. Using thermography, the temperature of breasts and eyes was measured as indirect reference of core body and room temperatures. To analyze the thermal behavior of the breasts during the cycle, the core body and room temperatures were normalized by means of a mathematical equation. We performed 180 observations and the core temperature had the highest correlation with the breast temperature, followed by room temperature. The proposed prediction model could explain 45.3% of the breast temperature variation, with variable room temperature variable; it can be accepted as a way to estimate the reference breast temperature at different room temperatures. The average breast temperature in healthy women had a direct relation with the core and room temperature and can be estimated mathematically. It is suggested that an equation could be used in clinical practice to estimate the normal breast reference temperature in young women, regardless of the day of the cycle, therefore assisting in evaluation of anatomical studies.

Metallic behavior of lanthanum disilicide

NASA Technical Reports Server (NTRS)

Long, Robert G.; Bost, M. C.; Mahan, John E.

1988-01-01

Polycrystalline thin films of LaSi2 were prepared by reaction of sputter-deposited lanthanum layers with silicon wafers. Samples of the low-temperature tetragonal and the high-temperature orthorhombic phases were separately obtained. The room-temperature intrinsic resistivities were 24 and 57 microohm cm for the low- and high-temperature structures, respectively. Although lanthanum disilicide had been previously reported to be a semiconductor, classical metallic behavior was found for both phases.

Structure and optical properties of evaporated films of the Cr- and V-group metals

NASA Technical Reports Server (NTRS)

Nestell, J. E., Jr.; Christy, R. W.; Cohen, M. H.; Ruben, G. C.

1980-01-01

Thin films of Cr, Mo, and W rapidly evaporated in high vacuum (5 x 10 to the -7th torr) onto room-temperature substrates show anomalously low reflectance (compared to bulk samples). From electron and X-ray diffraction and electron microscopy, the normal bcc crystal structure is found, but with very fine grains. Columnar grains about 100 A in diameter were separated by a less dense grain-boundary network about 10-A wide. The measured optical conductivity agrees with an inhomogeneous-medium model that assumes the normal crystalline conductivity for the grain interiors, with model parameters that correlate to the observed columnar grain size. In contrast, V and Nb films rapidly evaporated onto room-temperature substrates have the reflectance of bulk crystalline material. On liquid-nitrogen temperature substrates, however, V and Nb have normal bcc crystal structure but with small flat-plate grains, and the same model, with appropriate parameters, accounts for the optical conductivity. The difference between these two groups apparently depends on residual gases segregated at the grain boundaries in the Cr-group films.

Evolution of structural and optical properties of rutile TiO2 thin films synthesized at room temperature by chemical bath deposition method

NASA Astrophysics Data System (ADS)

Mayabadi, A. H.; Waman, V. S.; Kamble, M. M.; Ghosh, S. S.; Gabhale, B. B.; Rondiya, S. R.; Rokade, A. V.; Khadtare, S. S.; Sathe, V. G.; Pathan, H. M.; Gosavi, S. W.; Jadkar, S. R.

2014-02-01

Nanocrystalline thin films of TiO2 were prepared on glass substrates from an aqueous solution of TiCl3 and NH4OH at room temperature using the simple and cost-effective chemical bath deposition (CBD) method. The influence of deposition time on structural, morphological and optical properties was systematically investigated. TiO2 transition from a mixed anatase-rutile phase to a pure rutile phase was revealed by low-angle XRD and Raman spectroscopy. Rutile phase formation was confirmed by FTIR spectroscopy. Scanning electron micrographs revealed that the multigrain structure of as-deposited TiO2 thin films was completely converted into semi-spherical nanoparticles. Optical studies showed that rutile thin films had a high absorption coefficient and a direct bandgap. The optical bandgap decreased slightly (3.29-3.07 eV) with increasing deposition time. The ease of deposition of rutile thin films at low temperature is useful for the fabrication of extremely thin absorber (ETA) solar cells, dye-sensitized solar cells, and gas sensors.

Itinerant Antiferromagnetism in FeMnP 0.8Si 0.2

DOE PAGES

Sales, Brian C.; Susner, Michael A.; Conner, Benjamin S.; ...

2015-09-25

Compounds based on the Fe 2P structure have continued to attract interest because of the interplay between itinerant and localized magnetism in a noncentrosymmetric crystal structure, and because of the recent developments of these materials for magnetocaloric applications. We report the growth and characterization of millimeter-sized single crystals of FeMnP 0.8Si 0.2 with the Fe 2P structure. Single-crystal x-ray diffraction, magnetization, resistivity, and Hall and heat capacity data are reported. The crystals exhibit itinerant antiferromagnetic order below 158 K with no hint of ferromagnetic behavior in the magnetization curves and with the spins ordered primarily in the ab plane. Themore » room-temperature resistivity is close to the Ioffe-Regel limit for a metal. Single-crystal x-ray diffraction indicates a strong preference for Mn to occupy the larger pyramidal 3g site. The cation site preference in the as-grown crystals and the antiferromagnetism were not changed after high-temperature anneals and a rapid quench to room temperature« less

Electric modulation of conduction in multiferroic Ni-doped GaFeO3 ceramics

NASA Astrophysics Data System (ADS)

Ghani, Awais; Yang, Sen; Rajput, S. S.; Ahmed, S.; Murtaza, Adil; Zhou, Chao; Yu, Zhonghai; Zhang, Yin; Song, Xiaoping; Ren, Xiaobing

2018-06-01

In this work, the effects of Ni substitution on the electrical leakage and multiferroic properties of GaFeO3 were examined. Structural analysis of grown ceramics using x-ray diffraction and Raman shows that all ceramics have pure phases with an orthorhombic structure and space group. Ni substitutions slightly modify lattice parameters and induce lattice distortion within the same crystalline structure. It is observed that with increasing Ni-content up to 0.10, the magnetic transition temperature () increases from 196 K to 407 K. Ni-doped samples showed better ferroelectric properties and a drastic reduction in leakage current (~three orders of magnitude) at room temperature. Enhanced characteristics behavior is observed for 10% Ni substitution (GaFe0.9Ni0.1O3) and higher substitution leads to deterioration of properties with a larger leakage current. It is proposed that the role of Ni substitution can reduce hopping between Fe+3 and Fe+2 as well as suppressing the oxygen vacancies. This work would open new possibilities for integrating polycrystalline GaFeO3 at room temperature for magnetoelectric applications.

Electrical and Infrared Optical Properties of Vanadium Oxide Semiconducting Thin-Film Thermometers

NASA Astrophysics Data System (ADS)

Zia, Muhammad Fakhar; Abdel-Rahman, Mohamed; Alduraibi, Mohammad; Ilahi, Bouraoui; Awad, Ehab; Majzoub, Sohaib

2017-10-01

A synthesis method has been developed for preparation of vanadium oxide thermometer thin film for microbolometer application. The structure presented is a 95-nm thin film prepared by sputter-depositing nine alternating multilayer thin films of vanadium pentoxide (V2O5) with thickness of 15 nm and vanadium with thickness of 5 nm followed by postdeposition annealing at 300°C in nitrogen (N2) and oxygen (O2) atmospheres. The resulting vanadium oxide (V x O y ) thermometer thin films exhibited temperature coefficient of resistance (TCR) of -3.55%/°C with room-temperature resistivity of 2.68 Ω cm for structures annealed in N2 atmosphere, and TCR of -3.06%/°C with room-temperature resistivity of 0.84 Ω cm for structures annealed in O2 atmosphere. Furthermore, optical measurements of N2- and O2-annealed samples were performed by Fourier-transform infrared ellipsometry to determine their dispersion curves, refractive index ( n), and extinction coefficient ( k) at wavelength from 7000 nm to 14,000 nm. The results indicate the possibility of applying the developed materials in thermometers for microbolometers.

Intramolecular structural model for photoinduced plasticity in chalcogenide glasses

NASA Astrophysics Data System (ADS)

Yannopoulos, S. N.

2003-08-01

Selected spectral features of Raman spectra of glassy As2S3 subjected to elongation stress and sub-band-gap light illumination are analyzed and compared with polarization-dependent information obtained from the bulk glass at room temperature and near the glass transition temperature. The data are suggestive of specific structural changes which involve the transformation of atomic arrangements from realgarlike As4S4 molecules, originally present in virgin (untreated) fibers, into planar orpimentlike clusters. Implications of these atomic rearrangements to the incipient photoinduced fluidity—the onset of plastic deformation—in As2S3 glass are discussed. Kinetics of photoinduced plastic changes is compared to that of Raman spectra changes, revealing a qualitative similar behavior. An approximate estimation of the relative contribution of intermolecular rearrangements and the intramolecular structural mechanism proposed in this paper has revealed that the latter is responsible for almost 30% of the photoinduced elongation of the fiber’s length at room temperature. The proposed mechanism can as well serve as rationale for understanding the photoinduced volume expansion observed in chalcogenide glasses.

Self-irradiation damage to the local structure of plutonium and plutonium intermetallics

NASA Astrophysics Data System (ADS)

Booth, C. H.; Jiang, Yu; Medling, S. A.; Wang, D. L.; Costello, A. L.; Schwartz, D. S.; Mitchell, J. N.; Tobash, P. H.; Bauer, E. D.; McCall, S. K.; Wall, M. A.; Allen, P. G.

2013-03-01

The effect of self-irradiation damage on the local structure of δ-Pu, PuAl2, PuGa3, and other Pu intermetallics has been determined for samples stored at room temperature using the extended x-ray absorption fine-structure (EXAFS) technique. These measurements indicate that the intermetallic samples damage at a similar rate as indicated in previous studies of PuCoGa5. In contrast, δ-Pu data indicate a much slower damage accumulation rate. To explore the effect of storage temperature and possible room temperature annealing effects, we also collected EXAFS data on a δ-Pu sample that was held at less than 32 K for a two month period. This sample damaged much more quickly. In addition, the measurable damage was annealed out at above only 135 K. Data from samples of δ-Pu with different Ga concentrations and results on all samples collected from different absorption edges are also reported. These results are discussed in terms of the vibrational properties of the materials and the role of Ga in δ-Pu as a network former.

The 15-K neutron structure of saccharide-free concanavalin A.

PubMed

Blakeley, M P; Kalb, A J; Helliwell, J R; Myles, D A A

2004-11-23

The positions of the ordered hydrogen isotopes of a protein and its bound solvent can be determined by using neutron crystallography. Furthermore, by collecting neutron data at cryo temperatures, the dynamic disorder within a protein crystal is reduced, which may lead to improved definition of the nuclear density. It has proved possible to cryo-cool very large Con A protein crystals (>1.5 mm3) suitable for high-resolution neutron and x-ray structure analysis. We can thereby report the neutron crystal structure of the saccharide-free form of Con A and its bound water, including 167 intact D2O molecules and 60 oxygen atoms at 15 K to 2.5-A resolution, along with the 1.65-A x-ray structure of an identical crystal at 100 K. Comparison with the 293-K neutron structure shows that the bound water molecules are better ordered and have lower average B factors than those at room temperature. Overall, twice as many bound waters (as D2O) are identified at 15 K than at 293 K. We note that alteration of bound water orientations occurs between 293 and 15 K; such changes, as illustrated here with this example, could be important more generally in protein crystal structure analysis and ligand design. Methodologically, this successful neutron cryo protein structure refinement opens up categories of neutron protein crystallography, including freeze-trapped structures and cryo to room temperature comparisons.

In situ probing of doping- and stress-mediated phase transitions in a single-crystalline VO2 nanobeam by spatially resolved Raman spectroscopy

NASA Astrophysics Data System (ADS)

Chang, Sung-Jin; Park, Jong Bae; Lee, Gaehang; Kim, Hae Jin; Lee, Jin-Bae; Bae, Tae-Sung; Han, Young-Kyu; Park, Tae Jung; Huh, Yun Suk; Hong, Woong-Ki

2014-06-01

We demonstrate an experimental in situ observation of the temperature-dependent evolution of doping- and stress-mediated structural phase transitions in an individual single-crystalline VO2 nanobeam on a Au-coated substrate under exposure to hydrogen gas using spatially resolved Raman spectroscopy. The nucleation temperature of the rutile R structural phase in the VO2 nanobeam upon heating under hydrogen gas was lower than that under air. The spatial structural phase evolution behavior along the length of the VO2 nanobeam under hydrogen gas upon heating was much more inhomogeneous than that along the length of the same nanobeam under air. The triclinic T phase of the VO2 nanobeam upon heating under hydrogen gas transformed to the R phase and this R phase was stabilized even at room temperature in air after sample cooling. In particular, after the VO2 nanobeam with the R phase was annealed at approximately 250 °C in air, it exhibited the monoclinic M1 phase (not the T phase) at room temperature during heating and cooling cycles. These results were attributed to the interplay between hydrogen doping and stress associated with nanobeam-substrate interactions. Our study has important implications for engineering metal-insulator transition properties and developing functional devices based on VO2 nanostructures through doping and stress.We demonstrate an experimental in situ observation of the temperature-dependent evolution of doping- and stress-mediated structural phase transitions in an individual single-crystalline VO2 nanobeam on a Au-coated substrate under exposure to hydrogen gas using spatially resolved Raman spectroscopy. The nucleation temperature of the rutile R structural phase in the VO2 nanobeam upon heating under hydrogen gas was lower than that under air. The spatial structural phase evolution behavior along the length of the VO2 nanobeam under hydrogen gas upon heating was much more inhomogeneous than that along the length of the same nanobeam under air. The triclinic T phase of the VO2 nanobeam upon heating under hydrogen gas transformed to the R phase and this R phase was stabilized even at room temperature in air after sample cooling. In particular, after the VO2 nanobeam with the R phase was annealed at approximately 250 °C in air, it exhibited the monoclinic M1 phase (not the T phase) at room temperature during heating and cooling cycles. These results were attributed to the interplay between hydrogen doping and stress associated with nanobeam-substrate interactions. Our study has important implications for engineering metal-insulator transition properties and developing functional devices based on VO2 nanostructures through doping and stress. Electronic supplementary information (ESI) available: Illustration, photograph, Raman data, and EDX spectra. See DOI: 10.1039/c4nr01118j

Structure and Properties of Al and Ga- Doped ZnO

NASA Astrophysics Data System (ADS)

Temizer, Namik Kemal

Recently there is tremendous interest in Transparent conducting oxide (TCO) research due to the unlimited and exciting application areas. Current research is mostly focused on finding alternative low cost and sustainable materials in order to replace indium tin oxide (ITO), which caused serious concern due to the increasing cost of indium and chemical stability issues of ITO. The primary aim of this research is to develop alternative TCO materials with superior properties in order to increase the efficiency in optoelectronic applications, as well as to study the properties of these materials to fully characterize them. We have grown Al and Ga-doped ZnO films with an optimized composition under different deposition conditions in order to understand the effect of processing parameters on the film properties. We report a detailed investigation on the structure-property correlations in Ga and Al codoped ZnO films on c-sapphire substrates where the thin film microstructure varies from nanocrystalline to single crystal. We have achieved highly epitaxial films with very high optical transmittance (close to 90%) and low resistivity (˜110muO-cm) values. The films grown in an ambient oxygen partial pressure (PO2 ) of 50 mTorr and at growth temperatures from room temperature to 600°C showed semiconducting behavior, whereas samples grown at a Po2 of 1 mTorr showed metallic nature. The most striking feature is the occurrence of resistivity minima at relatively high temperatures around 110 K in films deposited at high temperatures. The structure-property correlations reveal that point defects play an important role in modifying the structural, optical, electrical and magnetic properties and such changes in physical properties are controlled predominantly by the defect content. To gain a better understanding of the conduction processes in doped ZnO thin films, we have studied the temperature variation of resistivity of some selected samples that showed some interesting behavior. Micro-structural, transport, optical and magnetic properties in ZnGa0.002Al 0.02O films grown by pulsed laser deposition under different growth conditions was studied. In ZnO films grown at substrate temperatures of 600°C most interesting features are the concomitant occurrence of high temperature resistivity minima and room temperature ferromagnetism with a high saturation magnetic moment and considerable coercivity. The temperature dependent resistivity data has been interpreted in the light of quantum corrections to conductivity in disordered systems, suggesting that the e-e interactions is the dominant mechanism in the weak-localization (WL) limit in the case of films showing resistivity minima. We propose that formation of oxygen vacancy-Zinc interstitial defect complex (VO-IZn) is responsible for the enhancement in n-type conductivity, and zinc vacancies (VZn) for the observed room temperature ferromagnetism. ZnO nanostructures are gaining importance in various applications, from gas sensing to thin film transistors (TFTs). We have studied the micro-structural, transport, optical and magnetic properties in ZnO nanostructured films grown by pulsed laser deposition under different ambient conditions. We have investigated the nanostructures in detail through x-ray diffraction, SEM and TEM techniques. We have achieved relatively low room temperature resistivity and the occurrence of room temperature ferromagnetism with significant saturation magnetic moment of 1000 A/m with coercivity in the range of 100-150 Oe. Photoluminescence measurements were conducted to get an insight about the types of defects that occur under different growth conditions. Correlations between transport, optical and magnetic properties has been established in terms of these defects and their complexes. These nanostructured oxides with magnetic and optical properties are promising candidates in multifunctional spintronic and photonic devices.

Magnetization and anisotropy of cobalt ferrite thin films

NASA Astrophysics Data System (ADS)

Eskandari, F.; Porter, S. B.; Venkatesan, M.; Kameli, P.; Rode, K.; Coey, J. M. D.

2017-12-01

The magnetization of thin films of cobalt ferrite frequently falls far below the bulk value of 455 kA m-1 , which corresponds to an inverse cation distribution in the spinel structure with a significant orbital moment of about 0.6 μB that is associated with the octahedrally coordinated Co2+ ions. The orbital moment is responsible for the magnetostriction and magnetocrystalline anisotropy and its sensitivity to imposed strain. We have systematically investigated the structure and magnetism of films produced by pulsed-laser deposition on different substrates (Ti O2 , MgO, MgA l2O4 , SrTi O3 , LSAT, LaAl O3 ) and as a function of temperature (500 -700 °C) and oxygen pressure (10-4-10 Pa ) . Magnetization at room-temperature ranges from 60 to 440 kA m-1 , and uniaxial substrate-induced anisotropy ranges from +220 kJ m-3 for films on deposited on MgO (100) to -2100 kJ m-3 for films deposited on MgA l2O4 (100), where the room-temperature anisotropy field reaches 14 T. No rearrangement of high-spin Fe3+ and Co2+ cations on tetrahedral and octahedral sites can reduce the magnetization below the bulk value, but a switch from Fe3+ and Co2+ to Fe2+ and low-spin Co3+ on octahedral sites will reduce the low-temperature magnetization to 120 kA m-1 , and a consequent reduction of Curie temperature can bring the room-temperature value to near zero. Possible reasons for the appearance of low-spin cobalt in the thin films are discussed.

The reduction and oxidation of ceria: A natural abundance triple oxygen isotope perspective

NASA Astrophysics Data System (ADS)

Hayles, Justin; Bao, Huiming

2015-06-01

Ceria (CeO2) is a heavily studied material in catalytic chemistry for use as an oxygen storage medium, oxygen partial pressure regulator, fuel additive, and for the production of syngas, among other applications. Ceria powders are readily reduced and lose structural oxygen when subjected to low pO2 and/or high temperature conditions. Such dis-stoichiometric ceria can then re-oxidize under higher pO2 and/or lower temperature by incorporating new oxygen into the previously formed oxygen site vacancies. Despite extensive studies on ceria, the mechanisms for oxygen adsorption-desorption, dissociation-association, and diffusion of oxygen species on ceria surface and within the crystal structure are not well known. We predict that a large kinetic oxygen isotope effect should accompany the release and incorporation of ceria oxygen. As the first attempt to determine the existence and the degree of the isotope effect, this study focuses on a set of simple room-temperature re-oxidation experiments that are also relevant to a laboratory procedure using ceria to measure the triple oxygen isotope composition of CO2. Triple-oxygen-isotope labeled ceria powders are heated at 700 °C and cooled under vacuum prior to exposure to air. By combining results from independent experimental sets with different initial oxygen isotope labels and using a combined mass-balance and triangulation approach, we have determined the isotope fractionation factors for both high temperature reduction in vacuum (⩽10-4 mbar) and room temperature re-oxidation in air. Results indicate that there is a 1.5‰ ± 0.8‰ increase in the δ18O value of ceria after being heated in vacuum at 700 °C for 1 h. When the vacuum is broken at room temperature, the previously heated ceria incorporates 3-19% of its final structural oxygen from air, with a δ18O value of 2.1-4.1+7.7 ‰ for the incorporated oxygen. The substantial incorporation of oxygen from air supports that oxygen mobility is high in vacancy-rich ceria during re-oxidation at room temperature. The quantified oxygen isotope fractionation factors are consistent with the direct involvement of O2 in the rate limiting step for ceria reoxidation in air at room temperature. While additional parameters may reduce some of the uncertainties in our approach, this study demonstrates that isotope effects can be an encouraging tool for studying oxygen transport kinetics in ceria and other oxides. In addition, our finding warns of the special cares and limits in using ceria as an exchange medium for laboratory triple oxygen isotope analysis of CO2 or other oxygen-bearing gases.

Long Periodic Structure of a Room-Temperature Ionic Liquid by High-Pressure Small-Angle X-Ray Scattering and Wide-Angle X-Ray Scattering: 1-Decyl-3-Methylimidazolium Chloride.

PubMed

Abe, Hiroshi; Hamaya, Nozomu; Koyama, Yoshihiro; Kishimura, Hiroaki; Takekiyo, Takahiro; Yoshimura, Yukihiro; Wakabayashi, Daisuke; Funamori, Nobumasa; Matsuishi, Kiyoto

2018-04-23

The Bragg reflections of 1-decyl-3-methylimidazolium chloride ([C 10 mim][Cl]), a room-temperature ionic liquid, are observed in a lowly scattered wavevector (q) region using high-pressure (HP) small-angle X-ray scattering methods. The HP crystal of [C 10 mim][Cl] was characterized by an extremely long periodic structure. The peak position at the lowest q (1.4 nm -1 ) was different from that of the prepeak observed in the liquid state (2.3 nm -1 ). Simultaneously, Bragg reflections at high-q were detected using HP wide-angle X-ray scattering. The longest lattice constant was estimated to be 4.3 nm using structural analysis. The crystal structure of HP differed from that of the low-temperature (LT) crystal and the LT liquid crystal. With increasing pressure, Bragg reflections in the high-q component became much broader, and were accompanied by phase transition, although those in the low-q component were observed to be relatively sharp. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

High Electron Mobility SiGe/Si Transistor Structures on Sapphire Substrates

NASA Technical Reports Server (NTRS)

Alterovitz, Samuel A.; Mueller, Carl H.; Croke, Edward T.; Ponchak, George E.

2003-01-01

SiGe/Si n-type modulation doped field effect structures and transistors (n-MODFETs) have been fabricated on r-plane sapphire substrates. The structures were deposited using molecular beam epitaxy, and antimony dopants were incorporated via a delta doping process. Secondary ion mass spectroscopy (SIMS) indicates that the peak antimony, concentration was approximately 4 x 10(exp19) per cubic cm. The electron mobility was over 1,200 and 13,000 sq cm/V-sec at room temperature and 0.25 K, respectively. At these two temperatures, the electron carrier densities were 1.6 and 1.33 x 10(exp 12) per sq cm, thus demonstrating that carrier confinement was excellent. Shubnikov-de Haas oscillations were observed at 0.25 K, thus confirming the two-dimensional nature of the carriers. Transistors, with gate lengths varying from 1 micron to 5 microns, were fabricated using these structures and dc characterization was performed at room temperature. The saturated drain current region extended over a wide source-to-drain voltage (V(sub DS)) range, with (V(sub DS)) knee voltages of approximately 0.5 V and increased leakage starting at voltages slightly higher than 4 V.

Effect of the Conditions of the Nanostructuring Frictional Treatment Process on the Structural and Phase States and the Strengthening of Metastable Austenitic Steel

NASA Astrophysics Data System (ADS)

Makarov, A. V.; Skorynina, P. A.; Yurovskikh, A. S.; Osintseva, A. L.

2017-12-01

The effect of the multiplicity of frictional loading with a sliding synthetic diamond indenter at room temperature in an argon medium and the temperature of loading in the range of -196 to +250°C on the phase composition, fine structure, and micromechanical properties of the surface layer of metastable austenitic chromium-nickel steel has been studied. It has been established that the completeness of the strain-induced martensitic γ → α' transformation in the surface layer of steel is determined by the loading multiplicity and temperature, as well as the level of strengthening grows with an increase in the frictional loading multiplicity, but weakly depends on the frictional treatment temperature. According to the microindentation data, the characteristics of the surface layer strength and resistance to elastic and plastic deformation are improved with an increase in the frictional loading multiplicity. Frictional treatment by scanning with a synthetic diamond indenter at room and negative temperatures provides high quality for the treated surface with a low roughness parameter ( Ra = 80.115 nm), and an increase in the frictional loading temperature to 150-250°C leads to the development of a seizure and growth in Ra to 195-255 nm. Using transmission electron microscopy (TEM), it has been shown that frictional treatment results in the formation of nanocrystalline and fragmented submicrocrystalline structures of strain-induced α'-martensite (at a loading temperature of -196°C) and austenite (at a loading temperature of +250°C) in the surface layer of steel alongside with two-phase martensitic-austenitic structures (at a loading temperature of +20°C).

Temperature-resolved study of three [M(M'O4)4(TBPO)4] complexes (MM' = URe, ThRe, ThTc).

PubMed

Helliwell, Madeleine; Collison, David; John, Gordon H; May, Iain; Sarsfield, Mark J; Sharrad, Clint A; Sutton, Andrew D

2006-02-01

The crystal structures of the title complexes were measured at several temperatures between room temperature and 100 K. Each sample shows reversible crystal-to-crystal phase transitions as the temperature is varied. The behaviour of [U(ReO4)4(TBPO)4] (I) and [Th(ReO4)4(TBPO)4] (II) (TBPO = tri-n-butylphosphine oxide) is very similar; at room temperature, crystals of (I) and (II) are isostructural, with space group I42m, and reducing the temperature to 100 K causes a lowering of the space-group symmetry to C-centred cells, space groups Cc for (I) and Cmc2(1) for (II). The variation of lattice symmetry of [Th(TcO4)4(TBPO)4] (III) was found to be somewhat different, with the body-centred cubic space group, I43m, occurring at 293 K, a reduction of symmetry at 230 K to the C-centred orthorhombic space group, Cmc2(1), and a further transition to the primitive orthorhombic space group, Pbc2(1), below 215 K. Elucidation of the correct space-group symmetry and the subsequent refinement was complicated in some cases by the twinning by pseudo-merohedry that arises from the lowering of the space-group symmetry, occurring as the temperature is reduced. All three of the crystal structures determined at room temperature have high atomic displacement parameters, particularly of the (n)Bu groups, and (III) shows disorder of some of the O atoms. The structures in the space group Cmc2(1), show some disorder of nBu groups, but are otherwise reasonably well ordered; the structures of (I) in Cc and (III) in Pbc2(1) are ordered, even to the ends of the alkyl chains. Inter-comparison of the structures measured below 293 K, using the program OFIT from the SHELXTL package, showed that generally, they are remarkably alike, with weighted r.m.s. deviations of the M, M' and P atoms of less than 0.1 A, as are the 293 K structures of (I) and (II) with their low-temperature counterparts. However, the structure of (III) measured in the space group Cmc2(1) is significantly different from both the structure of (III) at 293 K and that found below 215 K, with weighted r.m.s. deviations of the Th, Tc and P atoms of 0.40 and 0.37 A, respectively. An extensive network of weak intra- and intermolecular C-H...O hydrogen bonds found between the atoms of the nBu and [M'O4] groups probably influences the packing and the overall geometry of the molecules.

A Na+ Superionic Conductor for Room-Temperature Sodium Batteries

NASA Astrophysics Data System (ADS)

Song, Shufeng; Duong, Hai M.; Korsunsky, Alexander M.; Hu, Ning; Lu, Li

2016-08-01

Rechargeable lithium ion batteries have ruled the consumer electronics market for the past 20 years and have great significance in the growing number of electric vehicles and stationary energy storage applications. However, in addition to concerns about electrochemical performance, the limited availability of lithium is gradually becoming an important issue for further continued use and development of lithium ion batteries. Therefore, a significant shift in attention has been taking place towards new types of rechargeable batteries such as sodium-based systems that have low cost. Another important aspect of sodium battery is its potential compatibility with the all-solid-state design where solid electrolyte is used to replace liquid one, leading to simple battery design, long life span, and excellent safety. The key to the success of all-solid-state battery design is the challenge of finding solid electrolytes possessing acceptable high ionic conductivities at room temperature. Herein, we report a novel sodium superionic conductor with NASICON structure, Na3.1Zr1.95Mg0.05Si2PO12 that shows high room-temperature ionic conductivity of 3.5 × 10-3 S cm-1. We also report successful fabrication of a room-temperature solid-state Na-S cell using this conductor.

Development of re-crystallized W-1.1%TiC with enhanced room-temperature ductility and radiation performance

NASA Astrophysics Data System (ADS)

Kurishita, H.; Matsuo, S.; Arakawa, H.; Sakamoto, T.; Kobayashi, S.; Nakai, K.; Takida, T.; Kato, M.; Kawai, M.; Yoshida, N.

2010-03-01

Ultra-fine grained (UFG) W-TiC compacts fabricated by powder metallurgical methods utilizing mechanical alloying (MA) are very promising for use in irradiation environments. However, the assurance of room-temperature ductility and enhancement in surface resistances to low-energy hydrogen irradiation are unsettled issues. As an approach to solution to these, microstructural modification by hot plastic working has been applied to UFG W-TiC processed by MA in a purified Ar or H 2 atmosphere and hot isostatic pressing (HIP). Hot plastically worked compacts have been subjected to 3-point bend tests at room temperature and TEM microstructural examinations. It is found that the microstructural modification allows us to convert UFG W-1.1%TiC to compacts exhibiting a very high fracture strength and appreciable ductility at room temperature. The compacts of W-1.1%TiC/Ar (MA atmosphere: Ar) and W-1.1%TiC/H 2 (MA atmosphere: H 2) exhibit re-crystallized structures with approximately 0.5 and 1.5 μm in grain size, respectively. It is shown that the enhancement of fracture resistance by microstructural modifications is attributed to significant strengthening of weak grain boundaries in the re-crystallized state. As a result the modified compacts exhibit superior surface resistance to low-energy deuteron irradiation.

Microwave-Accelerated Surface Modification of Plasmonic Gold Thin Films with Self-Assembled Monolayers of Alkanethiols

PubMed Central

Grell, Tsehai A.J.; Alabanza, Anginelle M.; Gaskell, Karen; Aslan, Kadir

2013-01-01

A rapid surface modification technique for the formation of self-assembled monolayers (SAMs) of alkanethiols on gold thin films using microwave heating in less than 10 min is reported. In this regard, SAMs of two model alkanethiols, 11-mercaptoundecanoic acid (11-MUDA, to generate a hydrophilic surface) and undecanethiol (UDET, a hydrophobic surface), were successfully formed on gold thin films using selective microwave heating in 1) a semi-continuous and 2) a continuous fashion and at room temperature (24 hours, control experiment, no microwave heating). The formation of SAMs of 11-MUDA and UDET were confirmed by contact angle measurements, Fourier–transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The contact angles for water on SAMs formed by the selective microwave heating and conventional room temperature incubation technique (24 hours) were measured to be similar for 11-MUDA and UDET. FT-IR spectroscopy results confirmed that the internal structure of SAMs prepared using both microwave heating and at room temperature were similar. XPS results revealed that the organic and sulfate contaminants found on bare gold thin films were replaced by SAMs after the surface modification process was carried out using both microwave heating and at room temperature. PMID:24083414

A Na+ Superionic Conductor for Room-Temperature Sodium Batteries

PubMed Central

Song, Shufeng; Duong, Hai M.; Korsunsky, Alexander M.; Hu, Ning; Lu, Li

2016-01-01

Rechargeable lithium ion batteries have ruled the consumer electronics market for the past 20 years and have great significance in the growing number of electric vehicles and stationary energy storage applications. However, in addition to concerns about electrochemical performance, the limited availability of lithium is gradually becoming an important issue for further continued use and development of lithium ion batteries. Therefore, a significant shift in attention has been taking place towards new types of rechargeable batteries such as sodium-based systems that have low cost. Another important aspect of sodium battery is its potential compatibility with the all-solid-state design where solid electrolyte is used to replace liquid one, leading to simple battery design, long life span, and excellent safety. The key to the success of all-solid-state battery design is the challenge of finding solid electrolytes possessing acceptable high ionic conductivities at room temperature. Herein, we report a novel sodium superionic conductor with NASICON structure, Na3.1Zr1.95Mg0.05Si2PO12 that shows high room-temperature ionic conductivity of 3.5 × 10−3 S cm−1. We also report successful fabrication of a room-temperature solid-state Na-S cell using this conductor. PMID:27572915

A Na(+) Superionic Conductor for Room-Temperature Sodium Batteries.

PubMed

Song, Shufeng; Duong, Hai M; Korsunsky, Alexander M; Hu, Ning; Lu, Li

2016-08-30

Rechargeable lithium ion batteries have ruled the consumer electronics market for the past 20 years and have great significance in the growing number of electric vehicles and stationary energy storage applications. However, in addition to concerns about electrochemical performance, the limited availability of lithium is gradually becoming an important issue for further continued use and development of lithium ion batteries. Therefore, a significant shift in attention has been taking place towards new types of rechargeable batteries such as sodium-based systems that have low cost. Another important aspect of sodium battery is its potential compatibility with the all-solid-state design where solid electrolyte is used to replace liquid one, leading to simple battery design, long life span, and excellent safety. The key to the success of all-solid-state battery design is the challenge of finding solid electrolytes possessing acceptable high ionic conductivities at room temperature. Herein, we report a novel sodium superionic conductor with NASICON structure, Na3.1Zr1.95Mg0.05Si2PO12 that shows high room-temperature ionic conductivity of 3.5 × 10(-3) S cm(-1). We also report successful fabrication of a room-temperature solid-state Na-S cell using this conductor.

Synthesis of AuPd alloyed nanoparticles via room-temperature electron reduction with argon glow discharge as electron source.

PubMed

Yang, Manman; Wang, Zongyuan; Wang, Wei; Liu, Chang-Jun

2014-01-01

Argon glow discharge has been employed as a cheap, environmentally friendly, and convenient electron source for simultaneous reduction of HAuCl4 and PdCl2 on the anodic aluminum oxide (AAO) substrate. The thermal imaging confirms that the synthesis is operated at room temperature. The reduction is conducted with a short time (30 min) under the pressure of approximately 100 Pa. This room-temperature electron reduction operates in a dry way and requires neither hydrogen nor extra heating nor chemical reducing agent. The analyses using X-ray photoelectron spectroscopy (XPS) confirm all the metallic ions have been reduced. The characterization with X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) shows that AuPd alloyed nanoparticles are formed. There also exist some highly dispersed Au and Pd monometallic particles that cannot be detected by XRD and transmission electron microscopy (TEM) because of their small particle sizes. The observed AuPd alloyed nanoparticles are spherical with an average size of 14 nm. No core-shell structure can be observed. The room-temperature electron reduction can be operated in a larger scale. It is an easy way for the synthesis of AuPd alloyed nanoparticles.

Radiation-induced hydroxyl addition to purine molecules: EPR and ENDOR study of hypoxanthine hydrochloride monohydrate single crystals.

PubMed

Tokdemir, Sibel; Nelson, William H

2005-06-01

Three radical species were detected in an EPR/ENDOR study of X-irradiated hypoxanthine.HCl.H2O single crystals at room temperature: RI was identified as the product of net H addition to C8, RII was identified as the product of net H addition to C2, and RIII was identified as the product of OH addition to C8. The observed set of radicals was the same for room-temperature irradiation as for irradiation at 10 K followed by warming the crystals to room temperature; however, the C2 H-addition and C8 OH-addition radicals were not detectable after storage of the crystals for about 2 months at room temperature. Use of selectively deuterated crystals permitted unique assignment of the observed hyperfine couplings, and results of density functional theory calculations on each of the radical structures were consistent with the experimental results. Comparison of these experimental results with others from previous crystal-based systems and model system computations provides insight into the mechanisms by which the biologically important purine C8 hydroxyl addition products are formed. The evidence from solid systems supports the mechanism of net water addition to one-electron oxidized purine bases and demonstrates the importance of a facial approach between the reactants.

On the polymorphism of benzocaine; a low-temperature structural phase transition for form (II).

PubMed

Chan, Eric J; Rae, A David; Welberry, T Richard

2009-08-01

A low-temperature structural phase transition has been observed for form (II) of benzocaine (BZC). Lowering the temperature doubles the b-axis repeat and changes the space group from P2(1)2(1)2(1) to P112(1) with gamma now 99.37 degrees. The structure is twinned, the twin rule corresponding to a 2(1) screw rotation parallel to a. The phase transition is associated with a sequential displacement parallel to a of zigzag bi-layers of ribbons perpendicular to b*. No similar phase transition was observed for form (I) and this was attributed to the different packing symmetries of the two room-temperature polymorphic forms.

Low Temperature Double-layer Capacitors with Improved Energy Density: An Overview of Recent Development Efforts

NASA Technical Reports Server (NTRS)

Brandon, Erik J.; West, William C.; Smart, Marshall C.; Korenblit, Yair; Kajdos, Adam; Kvit, Alexander; Jagiello, Jacek; Yushin, Gleb

2012-01-01

Electrochemical double-layer capacitors are finding increased use in a wide range of energy storage applications, particularly where high pulse power capabilities are required. Double-layer capacitors store charge at a liquid/solid interface, making them ideal for low temperature power applications, due to the facile kinetic processes associated with the rearrangement of the electrochemical double-layer at these temperatures. Potential low temperature applications include hybrid and electric vehicles, operations in polar regions, high altitude aircraft and aerospace avionics, and distributed environmental and structural health monitoring. State-of-the-art capacitors can typically operate to -40 C, with a subsequent degradation in power performance below room temperature. However, recent efforts focused on advanced electrolyte and electrode systems can enable operation to temperatures as low as -70 C, with capacities similar to room temperature values accompanied by reasonably low equivalent series resistances. This presentation will provide an overview of recent development efforts to extend and improve the wide temperature performance of these devices.

Thermoelectric Power Generation from Lanthanum Strontium Titanium Oxide at Room Temperature through the Addition of Graphene.

PubMed

Lin, Yue; Norman, Colin; Srivastava, Deepanshu; Azough, Feridoon; Wang, Li; Robbins, Mark; Simpson, Kevin; Freer, Robert; Kinloch, Ian A

2015-07-29

The applications of strontium titanium oxide based thermoelectric materials are currently limited by their high operating temperatures of >700 °C. Herein, we show that the thermal operating window of lanthanum strontium titanium oxide (LSTO) can be reduced to room temperature by the addition of a small amount of graphene. This increase in operating performance will enable future applications such as generators in vehicles and other sectors. The LSTO composites incorporated one percent or less of graphene and were sintered under an argon/hydrogen atmosphere. The resultant materials were reduced and possessed a multiphase structure with nanosized grains. The thermal conductivity of the nanocomposites decreased upon the addition of graphene, whereas the electrical conductivity and power factor both increased significantly. These factors, together with a moderate Seebeck coefficient, meant that a high power factor of ∼2500 μWm(-1)K(-2) was reached at room temperature at a loading of 0.6 wt % graphene. The highest thermoelectric figure of merit (ZT) was achieved when 0.6 wt % graphene was added (ZT = 0.42 at room temperature and 0.36 at 750 °C), with >280% enhancement compared to that of pure LSTO. A preliminary 7-couple device was produced using bismuth strontium cobalt oxide/graphene-LSTO pucks. This device had a Seebeck coefficient of ∼1500 μV/K and an open voltage of 600 mV at a mean temperature of 219 °C.

Enhanced High-Temperature Cyclic Stability of Al-Doped Manganese Dioxide and Morphology Evolution Study Through in situ NMR under High Magnetic Field.

PubMed

Huang, Shenggen; Sun, Jian; Yan, Jian; Liu, Jiaqin; Wang, Weijie; Qin, Qingqing; Mao, Wenping; Xu, Wei; Wu, Yucheng; Wang, Junfeng

2018-03-21

In this work, Al-doped MnO 2 (Al-MO) nanoparticles have been synthesized by a simple chemical method with the aim to enhance cycling stability. At room temperature and 50 °C, the specific capacitances of Al-MO are well-maintained after 10 000 cycles. Compared with pure MnO 2 nanospheres (180.6 F g -1 at 1 A g -1 ), Al-MO also delivers an enhanced specific capacitance of 264.6 F g -1 at 1 A g -1 . During the cycling test, Al-MO exhibited relatively stable structure initially and transformed to needlelike structures finally both at room temperature and high temperature. In order to reveal the morphology evolution process, in situ NMR under high magnetic field has been carried out to probe the dynamics of structural properties. The 23 Na spectra and the SEM observation suggest that the morphology evolution may follow pulverization/reassembling process. The Na + intercalation/deintercalation induced pulverization, leading to the formation of tiny MnO 2 nanoparticles. After that, the pulverized tiny nanoparticles reassembled into new structures. In Al-MO electrodes, doping of Al 3+ could slow down this structure evolution process, resulting in a better electrochemical stability. This work deepens the understanding on the structural changes in faradic reaction of pseudocapacitive materials. It is also important for the practical applications of MnO 2 -based supercapacitors.

Structural and electronic engineering of 3DOM WO3 by alkali metal doping for improved NO2 sensing performance

NASA Astrophysics Data System (ADS)

Wang, Zhihua; Fan, Xiaoxiao; Han, Dongmei; Gu, Fubo

2016-05-01

Novel alkali metal doped 3DOM WO3 materials were prepared using a simple colloidal crystal template method. Raman, XRD, SEM, TEM, XPS, PL, Hall and UV-Vis techniques were used to characterize the structural and electronic properties of all the products, while the corresponding sensing performances targeting ppb level NO2 were determined at different working temperatures. For the overall goal of structural and electronic engineering, the co-effect of structural and electronic properties on the improved NO2 sensing performance of alkali metal doped 3DOM WO3 was studied. The test results showed that the gas sensing properties of 3DOM WO3/Li improved the most, with the fast response-recovery time and excellent selectivity. More importantly, the response of 3DOM WO3/Li to 500 ppb NO2 was up to 55 at room temperature (25 °C). The especially high response to ppb level NO2 at room temperature (25 °C) in this work has a very important practical significance. The best sensing performance of 3DOM WO3/Li could be ascribed to the most structure defects and the highest carrier mobility. And the possible gas sensing mechanism based on the model of the depletion layer was proposed to demonstrate that both structural and electronic properties are responsible for the NO2 sensing behavior.Novel alkali metal doped 3DOM WO3 materials were prepared using a simple colloidal crystal template method. Raman, XRD, SEM, TEM, XPS, PL, Hall and UV-Vis techniques were used to characterize the structural and electronic properties of all the products, while the corresponding sensing performances targeting ppb level NO2 were determined at different working temperatures. For the overall goal of structural and electronic engineering, the co-effect of structural and electronic properties on the improved NO2 sensing performance of alkali metal doped 3DOM WO3 was studied. The test results showed that the gas sensing properties of 3DOM WO3/Li improved the most, with the fast response-recovery time and excellent selectivity. More importantly, the response of 3DOM WO3/Li to 500 ppb NO2 was up to 55 at room temperature (25 °C). The especially high response to ppb level NO2 at room temperature (25 °C) in this work has a very important practical significance. The best sensing performance of 3DOM WO3/Li could be ascribed to the most structure defects and the highest carrier mobility. And the possible gas sensing mechanism based on the model of the depletion layer was proposed to demonstrate that both structural and electronic properties are responsible for the NO2 sensing behavior. Electronic supplementary information (ESI) available: Raman, SEM, TEM, mapping, XPS and PL images; transient plot; response of 3DOM WO3/Li to NO2 concentration, sensing stability and the corresponding log (Sg - 1) versus log Cg curves. See DOI: 10.1039/c6nr00858e

A novel metal-organic framework for high storage and separation of acetylene at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Xing, E-mail: star1987@hdu.edu.cn; Wang, Huizhen; Ji, Zhenguo

2016-09-15

A novel 3D microporous metal-organic framework with NbO topology, [Cu{sub 2}(L)(H{sub 2}O){sub 2}]∙(DMF){sub 6}·(H{sub 2}O){sub 2} (ZJU-10, ZJU = Zhejiang University; H{sub 4}L =2′-hydroxy-[1,1′:4′,1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid; DMF =N,N-dimethylformamide), has been synthesized and structurally characterized. With suitable pore sizes and open Cu{sup 2+} sites, ZJU-10a exhibits high BET surface area of 2392 m{sup 2}/g, as well as moderately high C{sub 2}H{sub 2} volumetric uptake capacity of 132 cm{sup 3}/cm{sup 3}. Meanwhile, ZJU-10a is a promising porous material for separation of acetylene from methane and carbon dioxide gas mixtures at room temperature. - Graphical abstract: A new NbO-type microporous metal-organic framework ZJU-10 withmore » suitable pore size and open Cu{sup 2+} sites was synthesized to realize the strong interaction with acetylene molecules, which can separate the acetylene from methane and carbon dioxane gas mixtures at room temperature. Display Omitted - Highlights: • A novel 3D NbO-type microporous metal-organic framework ZJU-10 was solvothermally synthesized and structurally characterized. • ZJU-10a exhibits high BET surface area of 2392 m{sup 2}/g. • ZJU-10a shows a moderately high C{sub 2}H{sub 2} gravimetric (volumetric) uptake capacity of 174 (132) cm{sup 3}/g at 298 K and 1 bar. • ZJU-10a can separate acetylene from methane and carbon dioxide gas mixtures at room temperature.« less

Enhanced magnetocaloric properties and critical behavior of (Fe0.72Cr0.28)3Al alloys for near room temperature cooling

NASA Astrophysics Data System (ADS)

Sharma, V.; Maheshwar Repaka, D. V.; Chaudhary, V.; Ramanujan, R. V.

2017-04-01

Magnetic cooling is an environmentally friendly, energy efficient, thermal management technology relying on high performance magnetocaloric materials (MCM). Current research has focused on low cost, corrosion resistant, rare earth (RE) free MCMs. We report the structural and magnetocaloric properties of novel, low cost, RE free, iron based (Fe0.72Cr0.28)3Al alloys. The arc melted buttons and melt spun ribbons possessed the L21 crystal structure and B2 crystal structure, respectively. A notable enhancement of 33% in isothermal entropy change (-ΔS m) and 25% increase in relative cooling power (RCP) for the ribbons compared to the buttons can be attributed to higher structural disorder in the Fe-Cr and Fe-Al sub-lattices of the B2 structure. The critical behavior was investigated using modified Arrott plots, the Kouvel-Fisher plot and the critical isotherm technique; the critical exponents were found to correspond to the short-range order 3D Heisenberg model. The field and temperature dependent magnetization curves of (Fe0.72Cr0.28)3Al alloys revealed their soft magnetic nature with negligible hysteresis. Thus, these alloys possess promising performance attributes for near room temperature magnetic cooling applications.

Reference breast temperature: proposal of an equation

PubMed Central

de Souza, Gladis Aparecida Galindo Reisemberger; Brioschi, Marcos Leal; Vargas, José Viriato Coelho; Morais, Keli Cristiane Correia; Dalmaso, Carlos; Neves, Eduardo Borba

2015-01-01

ABSTRACT Objective To develop an equation to estimate the breast reference temperature according to the variation of room and core body temperatures. Methods Four asymptomatic women were evaluated for three consecutive menstrual cycles. Using thermography, the temperature of breasts and eyes was measured as indirect reference of core body and room temperatures. To analyze the thermal behavior of the breasts during the cycle, the core body and room temperatures were normalized by means of a mathematical equation. Results We performed 180 observations and the core temperature had the highest correlation with the breast temperature, followed by room temperature. The proposed prediction model could explain 45.3% of the breast temperature variation, with variable room temperature variable; it can be accepted as a way to estimate the reference breast temperature at different room temperatures. Conclusion The average breast temperature in healthy women had a direct relation with the core and room temperature and can be estimated mathematically. It is suggested that an equation could be used in clinical practice to estimate the normal breast reference temperature in young women, regardless of the day of the cycle, therefore assisting in evaluation of anatomical studies. PMID:26761549

Local Magnetic Measurements of Trapped Flux Through a Permanent Current Path in Graphite

NASA Astrophysics Data System (ADS)

Stiller, Markus; Esquinazi, Pablo D.; Quiquia, José Barzola; Precker, Christian E.

2018-04-01

Temperature- and field-dependent measurements of the electrical resistance of different natural graphite samples suggest the existence of superconductivity at room temperature in some regions of the samples. To verify whether dissipationless electrical currents are responsible for the trapped magnetic flux inferred from electrical resistance measurements, we localized them using magnetic force microscopy on a natural graphite sample in remanent state after applying a magnetic field. The obtained evidence indicates that at room temperature a permanent current flows at the border of the trapped flux region. The current path vanishes at the same transition temperature T_c≈ 370 K as the one obtained from electrical resistance measurements on the same sample. This sudden decrease in the phase is different from what is expected for a ferromagnetic material. Time-dependent measurements of the signal show the typical behavior of flux creep of a permanent current flowing in a superconductor. The overall results support the existence of room-temperature superconductivity at certain regions in the graphite structure and indicate that magnetic force microscopy is suitable to localize them. Magnetic coupling is excluded as origin of the observed phase signal.

TOPICAL REVIEW: Protein stability and enzyme activity at extreme biological temperatures

NASA Astrophysics Data System (ADS)

Feller, Georges

2010-08-01

Psychrophilic microorganisms thrive in permanently cold environments, even at subzero temperatures. To maintain metabolic rates compatible with sustained life, they have improved the dynamics of their protein structures, thereby enabling appropriate molecular motions required for biological activity at low temperatures. As a consequence of this structural flexibility, psychrophilic proteins are unstable and heat-labile. In the upper range of biological temperatures, thermophiles and hyperthermophiles grow at temperatures > 100 °C and synthesize ultra-stable proteins. However, thermophilic enzymes are nearly inactive at room temperature as a result of their compactness and rigidity. At the molecular level, both types of extremophilic proteins have adapted the same structural factors, but in opposite directions, to address either activity at low temperatures or stability in hot environments. A model based on folding funnels is proposed accounting for the stability-activity relationships in extremophilic proteins.

Solid-state diffusion-controlled growth of the phases in the Au-Sn system

NASA Astrophysics Data System (ADS)

Baheti, Varun A.; Kashyap, Sanjay; Kumar, Praveen; Chattopadhyay, Kamanio; Paul, Aloke

2018-01-01

The solid state diffusion-controlled growth of the phases is studied for the Au-Sn system in the range of room temperature to 200 °C using bulk and electroplated diffusion couples. The number of product phases in the interdiffusion zone decreases with the decrease in annealing temperature. These phases grow with significantly high rates even at the room temperature. The growth rate of the AuSn4 phase is observed to be higher in the case of electroplated diffusion couple because of the relatively small grains and hence high contribution of the grain boundary diffusion when compared to the bulk diffusion couple. The diffraction pattern analysis indicates the same equilibrium crystal structure of the phases in these two types of diffusion couples. The analysis in the AuSn4 phase relating the estimated tracer diffusion coefficients with grain size, crystal structure, the homologous temperature of experiments and the concept of the sublattice diffusion mechanism in the intermetallic compounds indicate that Au diffuses mainly via the grain boundaries, whereas Sn diffuses via both the grain boundaries and the lattice.

Structural versus electrical properties of an organic-inorganic hybrid material based on sulfate

NASA Astrophysics Data System (ADS)

Ben Rached, Asma; Guionneau, Philippe; Lebraud, Eric; Mhiri, Tahar; Elaoud, Zakaria

2017-01-01

A new organo-sulfate compound is obtained by slow evaporation at room temperature and is characterized by powder and single-crystal X-ray diffraction (XRD) at variable temperatures. The benzylammonium monohydrogenosulfate of formula C6H5CH2NH3+. HSO4-, denoted (BAS), crystallizes in the monoclinic system P21/c space group with the following parameters at room temperature: a=5.623(5)Å, b=20.239(5) Å, c=8.188(5)Å, β=94.104(5)°. The crystal structure consists of infinite parallel two-dimensional planes built by HSO4- anions and C6H5CH2NH3+ cations interconnected by strong O-H….. O and N-H….. O hydrogen bonds. A phase transition is detected at 350 K by differential scanning calorimetry (DSC) and confirmed by powder XRD. Conductivity measurements using the impedance spectroscopy technique allow to determine the conductivity relaxation parameters associated with the H+ conduction from an analysis of the M"/M"max spectrum measured in a wide temperature range. Transport properties of this material appear to be due to an H+ ion hopping mechanism.

Lithium ion conduction in sol-gel synthesized LiZr2(PO4)3 polymorphs

NASA Astrophysics Data System (ADS)

Kumar, Milind; Yadav, Arun Kumar; Anita, Sen, Somaditya; Kumar, Sunil

2018-04-01

Safety issue associated with the high flammability and volatility of organic electrolytes used in commercial rechargeable lithium ion batteries has led to significant attention to ceramic-based solid electrolytes. In the present study, lithium ion conduction in two polymorphs of LiZr2(PO4)3 synthesized via the sol-gel route has been investigated. Rietveld refinement of room temperature X-ray diffraction data of LiZr2(PO4)3 powders calcined at 900 °C and 1300 °C confirmed these to be the monoclinic phase with P21/n structure and rhombohedral phase with R3¯c structure, respectively. Increase in calcination temperature and resultant phase transformation improved the room temperature conductivity from 2.27×10-6 ohm-1m-1 for the monoclinic phase to 1.41×10-4 ohm-1m-1 for rhombohedral phase. Temperature dependence of conductivity was modeled using Arrhenius law and activation energy of ˜ 0.59 eV (for monoclinic phase) and ˜0.50 eV (for rhombohedral phase) were obtained.

Shelf-life of bioprosthetic heart valves: a structural and mechanical study.

PubMed

Julien, M; Létouneau, D R; Marois, Y; Cardou, A; King, M W; Guidoin, R; Chachra, D; Lee, J M

1997-04-01

This study was undertaken to evaluate the influence of storage conditions on the shelf-life of porcine bioprosthetic valves. Fifty-five unimplanted porcine bioprostheses have been evaluated. The valves were stored in 0.5% buffered glutaraldehyde solution for different periods of time (7, 23 and 32 months). Twenty-eight valves were refrigerated while the remaining valves were stored at room temperature. The pH of the glutaraldehyde solution at room temperature decreased with time of storage, while that kept in the refrigerator remained stable over the course of the study. Macroscopic observations showed that the valve tissues kept at room temperature, especially for the periods of 23 and 32 months, became darker and more yellow in colour, whereas the refrigerated specimens exhibited no such changes in appearance. Scanning electron microscopy analysis revealed no noticeable differences on the surfaces of the leaflets stored under different conditions. Mechanical tests, including stress-strain response, stress relaxation and fracture behaviour, were carried out. Analysis of variance showed that the storage temperature, but not the length of storage, had a significant effect on some mechanical properties. The stress relaxation at 1000 s (P = 0.05), the ultimate tensile strength (P = 0.01) and the strain at fracture (P = 0.04) were all higher after storage at room temperature compared to the results after refrigeration. No statistically significant changes in the denaturation temperature of the collagen were observed between the different storage conditions. In conclusion, the storage temperature appears to have some influence on the bioprosthetic tissue. The bioprostheses stored under ambient conditions experience changes which may influence their longterm in vivo performance.

Structure of photosystem II and substrate binding at room temperature.

PubMed

Young, Iris D; Ibrahim, Mohamed; Chatterjee, Ruchira; Gul, Sheraz; Fuller, Franklin; Koroidov, Sergey; Brewster, Aaron S; Tran, Rosalie; Alonso-Mori, Roberto; Kroll, Thomas; Michels-Clark, Tara; Laksmono, Hartawan; Sierra, Raymond G; Stan, Claudiu A; Hussein, Rana; Zhang, Miao; Douthit, Lacey; Kubin, Markus; de Lichtenberg, Casper; Long Vo, Pham; Nilsson, Håkan; Cheah, Mun Hon; Shevela, Dmitriy; Saracini, Claudio; Bean, Mackenzie A; Seuffert, Ina; Sokaras, Dimosthenis; Weng, Tsu-Chien; Pastor, Ernest; Weninger, Clemens; Fransson, Thomas; Lassalle, Louise; Bräuer, Philipp; Aller, Pierre; Docker, Peter T; Andi, Babak; Orville, Allen M; Glownia, James M; Nelson, Silke; Sikorski, Marcin; Zhu, Diling; Hunter, Mark S; Lane, Thomas J; Aquila, Andy; Koglin, Jason E; Robinson, Joseph; Liang, Mengning; Boutet, Sébastien; Lyubimov, Artem Y; Uervirojnangkoorn, Monarin; Moriarty, Nigel W; Liebschner, Dorothee; Afonine, Pavel V; Waterman, David G; Evans, Gwyndaf; Wernet, Philippe; Dobbek, Holger; Weis, William I; Brunger, Axel T; Zwart, Petrus H; Adams, Paul D; Zouni, Athina; Messinger, Johannes; Bergmann, Uwe; Sauter, Nicholas K; Kern, Jan; Yachandra, Vittal K; Yano, Junko

2016-12-15

Light-induced oxidation of water by photosystem II (PS II) in plants, algae and cyanobacteria has generated most of the dioxygen in the atmosphere. PS II, a membrane-bound multi-subunit pigment protein complex, couples the one-electron photochemistry at the reaction centre with the four-electron redox chemistry of water oxidation at the Mn 4 CaO 5 cluster in the oxygen-evolving complex (OEC). Under illumination, the OEC cycles through five intermediate S-states (S 0 to S 4 ), in which S 1 is the dark-stable state and S 3 is the last semi-stable state before O-O bond formation and O 2 evolution. A detailed understanding of the O-O bond formation mechanism remains a challenge, and will require elucidation of both the structures of the OEC in the different S-states and the binding of the two substrate waters to the catalytic site. Here we report the use of femtosecond pulses from an X-ray free electron laser (XFEL) to obtain damage-free, room temperature structures of dark-adapted (S 1 ), two-flash illuminated (2F; S 3 -enriched), and ammonia-bound two-flash illuminated (2F-NH 3 ; S 3 -enriched) PS II. Although the recent 1.95 Å resolution structure of PS II at cryogenic temperature using an XFEL provided a damage-free view of the S 1 state, measurements at room temperature are required to study the structural landscape of proteins under functional conditions, and also for in situ advancement of the S-states. To investigate the water-binding site(s), ammonia, a water analogue, has been used as a marker, as it binds to the Mn 4 CaO 5 cluster in the S 2 and S 3 states. Since the ammonia-bound OEC is active, the ammonia-binding Mn site is not a substrate water site. This approach, together with a comparison of the native dark and 2F states, is used to discriminate between proposed O-O bond formation mechanisms.

Exploring the high-pressure behavior of the three known polymorphs of BiPO{sub 4}: Discovery of a new polymorph

DOE Office of Scientific and Technical Information (OSTI.GOV)

Errandonea, D., E-mail: daniel.errandonea@uv.es; García-Domene, B.; Gomis, O.

We have studied the structural behavior of bismuth phosphate under compression. We performed x-ray powder diffraction measurements up to 31.5 GPa and ab initio calculations. Experiments were carried out on different polymorphs: trigonal (phase I) and monoclinic (phases II and III). Phases I and III, at low pressure (P < 0.2–0.8 GPa), transform into phase II, which has a monazite-type structure. At room temperature, this polymorph is stable up to 31.5 GPa. Calculations support these findings and predict the occurrence of an additional transition from the monoclinic monazite-type to a tetragonal scheelite-type structure (phase IV). This transition was experimentally found after the simultaneous applicationmore » of pressure (28 GPa) and temperature (1500 K), suggesting that at room temperature the transition might by hindered by kinetic barriers. Calculations also predict an additional phase transition at 52 GPa, which exceeds the maximum pressure achieved in the experiments. This transition is from phase IV to an orthorhombic barite-type structure (phase V). We also studied the axial and bulk compressibility of BiPO{sub 4}. Room-temperature pressure-volume equations of state are reported. BiPO{sub 4} was found to be more compressible than isomorphic rare-earth phosphates. The discovered phase IV was determined to be the less compressible polymorph of BiPO{sub 4}. On the other hand, the theoretically predicted phase V has a bulk modulus comparable with that of monazite-type BiPO{sub 4}. Finally, the isothermal compressibility tensor for the monazite-type structure is reported at 2.4 GPa showing that the direction of maximum compressibility is in the (0 1 0) plane at approximately 15° (21°) to the a axis for the case of our experimental (theoretical) study.« less

Fabrication and Microstructure of Hydroxyapatite Coatings on Zirconia by Room Temperature Spray Process.

PubMed

Seo, Dong Seok; Chae, Hak Cheol; Lee, Jong Kook

2015-08-01

Hydroxyapatite coatings were fabricated on zirconia substrates by a room temperature spray process and were investigated with regards to their microstructure, composition and dissolution in water. An initial hydroxyapatite powder was prepared by heat treatment of bovine-bone derived powder at 1100 °C for 2 h, while dense zirconia substrates were fabricated by pressing 3Y-TZP powder and sintering it at 1350 °C for 2 h. Room temperature spray coating was performed using a slit nozzle in a low pressure-chamber with a controlled coating time. The phase composition of the resultant hydroxyapatite coatings was similar to that of the starting powder, however, the grain size of the hydroxyapatite particles was reduced to about 100 nm due to their formation by particle impaction and fracture. All areas of the coating had a similar morphology, consisting of reticulated structure with a high surface roughness. The hydroxyapatite coating layer exhibited biostability in a stimulated body fluid, with no severe dissolution being observed during in vitro experimentation.

Improved room-temperature luminescence of core-shell InGaAs/GaAs nanopillars via lattice-matched passivation

NASA Astrophysics Data System (ADS)

Komolibus, Katarzyna; Scofield, Adam C.; Gradkowski, Kamil; Ochalski, Tomasz J.; Kim, Hyunseok; Huffaker, Diana L.; Huyet, Guillaume

2016-02-01

Optical properties of GaAs/InGaAs/GaAs nanopillars (NPs) grown on GaAs(111)B were investigated. Employment of a mask-etching technique allowed for an accurate control over the geometry of NP arrays in terms of both their diameter and separation. This work describes both the steady-state and time-resolved photoluminescence of these structures as a function of the ensemble geometry, composition of the insert, and various shell compounds. The effects of the NP geometry on a parasitic radiative recombination channel, originating from an overgrown lateral sidewall layer, are discussed. Optical characterization reveals a profound influence of the core-shell lattice mismatch on the carrier lifetime and emission quenching at room temperature. When the lattice-matching conditions are satisfied, an efficient emission from the NP arrays at room temperature and below the band-gap of silicon is observed, clearly highlighting their potential application as emitters in optical interconnects integrated with silicon platforms.

ZnO nanomaterials based surface acoustic wave ethanol gas sensor.

PubMed

Wu, Y; Li, X; Liu, J H; He, Y N; Yu, L M; Liu, W H

2012-08-01

ZnO nanomaterials based surface acoustic wave (SAW) gas sensor has been investigated in ethanol environment at room temperature. The ZnO nanomaterials have been prepared through thermal evaporation of high-purity zinc powder. The as-prepared ZnO nanomaterials have been characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray Diffraction (XRD) techniques. The results indicate that the obtained ZnO nanomaterials, including many types of nanostructures such as nanobelts, nanorods, nanowires as well as nanosheets, are wurtzite with hexagonal structure and well-crystallized. The SAW sensor coated with the nanostructured ZnO materials has been tested in ethanol gas of various concentrations at room temperature. A network analyzer is used to monitor the change of the insertion loss of the SAW sensor when exposed to ethanol gas. The insertion loss of the SAW sensor varies significantly with the change of ethanol concentration. The experimental results manifest that the ZnO nanomaterials based SAW ethanol gas sensor exhibits excellent sensitivity and good short-term reproducibility at room temperature.

Facial development of high performance room temperature NO2 gas sensors based on ZnO nanowalls decorated rGO nanosheets

NASA Astrophysics Data System (ADS)

Liu, Zongyuan; Yu, Lingmin; Guo, Fen; Liu, Sheng; Qi, Lijun; Shan, Minyu; Fan, Xinhui

2017-11-01

A highly sensitive NO2 gas sensor based on ZnO nanowalls decorated rGO nanosheets was fabricated using a thermal reduction and soft solution process. The highly developed interconnected microporous networks of ZnO nanowalls were anchored homogeneously on the surface of reduced graphene oxide (rGO). Sensors fabricated with heterojunction structures achieved a higher response (S = 9.61) and shorter response-recovery (25 s, 15 s) behavior at room temperature to 50 ppm level NO2 effectively in contrast to those sensors based on net ZnO nanowalls or rGO layers. The stability and selectivity of ZnO/rGO heterojunction were carried out. Meanwhile, the effects of humidity on ZnO/rGO heterojunction gas sensor were investigated. The more preferable sensing performance of ZnO/rGO heterojunction to NO2 was discussed. It can be surmised that this NO2 gas sensor has potential for use as a portable room temperature gas sensor.

Full wafer size investigation of N+ and P+ co-implanted layers in 4H-SiC

NASA Astrophysics Data System (ADS)

Blanqué, S.; Lyonnet, J.; Pérez, R.; Terziyska, P.; Contreras, S.; Godignon, P.; Mestres, N.; Pascual, J.; Camassel, J.

2005-03-01

We report a full wafer size investigation of the homogeneity of electrical properties in the case of co-implanted nitrogen and phosphorus ions in 4H-SiC semi-insulating wafers. To match standard industrial requirements, implantation was done at room temperature. To achieve a detailed electrical knowledge, we worked on a 35 mm wafer on which 77 different reticules have been processed. Every reticule includes one Hall cross, one Van der Pauw test structure and different TLM patterns. Hall measurements have been made on all 77 different reticules, using an Accent HL5500 Hall System® from BioRad fitted with an home-made support to collect data from room temperature down to about 150 K. At room temperature, we find that the sheet carrier concentration is only 1/4 of the total implanted dose while the average mobility is 80.6 cm2/Vs. The standard deviation is, typically, 1.5 cm2/Vs.

Highly reliable contacts for lead-salt diode lasers

NASA Astrophysics Data System (ADS)

Lo, W.

1981-02-01

In order to improve the long term reliability of lead-salt diode lasers, ohmic contacts of multilayer, thin-film structures consisting of In plus Au, Pt, Ni, and Pd have been studied. Diode lasers of PbSnTe fabricated with a variety of contacts were tested during room-temperature storage and during accelerated aging tests. The results show that contact reliability can be improved when multiple overlapping films are used. After 4500 h of baking at 60 C, lasers with In-Au-Pd-Au contacts on both sides showed the least resistance increase (10%). For lasers with In-Au-Pt-Au contacts, 1 h of baking at 60 C is equivalent to 2 d storage at room temperature. Extrapolating these results, a 70% increase in contact resistance is expected for this type of laser after 9000 d of storage at room temperature. The data also suggests that a smaller increase in contact resistance can be expected for lasers fabricated with In-Au-Ni and In-Au-Pd-Au contacts.

Development of the α-IGZO/Ag/α-IGZO Triple-Layer Structure Films for the Application of Transparent Electrode.

PubMed

Chen, Kun-Neng; Yang, Cheng-Fu; Wu, Chia-Ching; Chen, Yu-Hsin

2017-02-24

We investigated the structural, optical, and electrical properties of amorphous IGZO/silver/amorphous IGZO (α-IGZO/Ag/α-IGZO) triple-layer structures that were deposited at room temperature on Eagle XG glass and flexible polyethylene terephthalate substrates through the sputtering method. Thin Ag layers with different thicknesses were inserted between two IGZO layers to form a triple-layer structure. Ag was used because of its lower absorption and resistivity. Field emission scanning electron microscopy measurements of the triple-layer structures revealed that the thicknesses of the Ag layers ranged from 13 to 41 nm. The thickness of the Ag layer had a large effect on the electrical and optical properties of the electrodes. The optimum thickness of the Ag metal thin film could be evaluated according to the optical transmittance, electrical conductivity, and figure of merit of the electrode. This study demonstrates that the α-IGZO/Ag/α-IGZO triple-layer transparent electrode can be fabricated with low sheet resistance (4.2 Ω/□) and high optical transmittance (88.1%) at room temperature without postannealing processing on the deposited thin films.

CuInP₂S₆ Room Temperature Layered Ferroelectric.

PubMed

Belianinov, A; He, Q; Dziaugys, A; Maksymovych, P; Eliseev, E; Borisevich, A; Morozovska, A; Banys, J; Vysochanskii, Y; Kalinin, S V

2015-06-10

We explore ferroelectric properties of cleaved 2-D flakes of copper indium thiophosphate, CuInP2S6 (CITP), and probe size effects along with limits of ferroelectric phase stability, by ambient and ultra high vacuum scanning probe microscopy. CITP belongs to the only material family known to display ferroelectric polarization in a van der Waals, layered crystal at room temperature and above. Our measurements directly reveal stable, ferroelectric polarization as evidenced by domain structures, switchable polarization, and hysteresis loops. We found that at room temperature the domain structure of flakes thicker than 100 nm is similar to the cleaved bulk surfaces, whereas below 50 nm polarization disappears. We ascribe this behavior to a well-known instability of polarization due to depolarization field. Furthermore, polarization switching at high bias is also associated with ionic mobility, as evidenced both by macroscopic measurements and by formation of surface damage under the tip at a bias of 4 V-likely due to copper reduction. Mobile Cu ions may therefore also contribute to internal screening mechanisms. The existence of stable polarization in a van-der-Waals crystal naturally points toward new strategies for ultimate scaling of polar materials, quasi-2D, and single-layer materials with advanced and nonlinear dielectric properties that are presently not found in any members of the growing "graphene family".

Crystalline Microporous Organosilicates with Reversed Functionalities of Organic and Inorganic Components for Room-Temperature Gas Sensing.

PubMed

Fabbri, Barbara; Bonoldi, Lucia; Guidi, Vincenzo; Cruciani, Giuseppe; Casotti, Davide; Malagù, Cesare; Bellussi, Giuseppe; Millini, Roberto; Montanari, Luciano; Carati, Angela; Rizzo, Caterina; Montanari, Erica; Zanardi, Stefano

2017-07-26

A deepened investigation on an innovative organic-inorganic hybrid material, referred to as ECS-14 (where ECS = Eni carbon silicates), revealed the possibility to use them as gas sensors. Indeed, among ECS phases, the crystalline state and the hexagonal microplateletlike morphology characteristic of ECS-14 seemed favorable properties to obtain continuous and uniform films. ECS-14 phase was used as functional material in screen-printable compositions and was thus deposited by drop coating for morphological, structural, thermal, and electrical characterizations. Possible operation at room temperature was investigated as technological progress, offering intrinsic safety in sensors working in harsh or industrial environments and avoiding high power consumption of most common sensors based on metal oxide semiconductors. Electrical characterization of the sensors based on ECS-14 versus concentrations of gaseous analytes gave significant results at room temperature in the presence of humidity, thereby demonstrating fundamental properties for a good quality sensor (speed, reversibility, and selectivity) that make them competitive with respect to systems currently in use. Remarkably, we observed functionality reversal of the organic and inorganic components; that is, in contrast to other hybrids, for ECS-14 the functional site has been ascribed to the inorganic phase while the organic component provided structural stability to the material. The sensing mechanism for humidity was also investigated.

Structure Evolution and Thermoelectric Properties of Carbonized Polydopamine Thin Films.

PubMed

Li, Haoqi; Aulin, Yaroslav V; Frazer, Laszlo; Borguet, Eric; Kakodkar, Rohit; Feser, Joseph; Chen, Yan; An, Ke; Dikin, Dmitriy A; Ren, Fei

2017-03-01

Carbonization of nature-inspired polydopamine can yield thin films with high electrical conductivity. Understanding of the structure of carbonized PDA (cPDA) is therefore highly desired. In this study, neutron diffraction, Raman spectroscopy, and other techniques indicate that cPDA samples are mainly amorphous with some short-range ordering and graphite-like structure that emerges with increasing heat treatment temperature. The electrical conductivity and the Seebeck coefficient show different trends with heat treatment temperature, while the thermal conductivity remains insensitive. The largest room-temperature ZT of 2 × 10 -4 was obtained on samples heat-treated at 800 °C, which is higher than that of reduced graphene oxide.

Structural evolution of nanoscale metallic glasses during high-pressure torsion: A molecular dynamics analysis

NASA Astrophysics Data System (ADS)

Feng, S. D.; Jiao, W.; Jing, Q.; Qi, L.; Pan, S. P.; Li, G.; Ma, M. Z.; Wang, W. H.; Liu, R. P.

2016-11-01

Structural evolution in nanoscale Cu50Zr50 metallic glasses during high-pressure torsion is investigated using molecular dynamics simulations. Results show that the strong cooperation of shear transformations can be realized by high-pressure torsion in nanoscale Cu50Zr50 metallic glasses at room temperature. It is further shown that high-pressure torsion could prompt atoms to possess lower five-fold symmetries and higher potential energies, making them more likely to participate in shear transformations. Meanwhile, a higher torsion period leads to a greater degree of forced cooperative flow. And the pronounced forced cooperative flow at room temperature under high-pressure torsion permits the study of the shear transformation, its activation and characteristics, and its relationship to the deformations behaviors. This research not only provides an important platform for probing the atomic-level understanding of the fundamental mechanisms of high-pressure torsion in metallic glasses, but also leads to higher stresses and homogeneous flow near lower temperatures which is impossible previously.

In-plane dielectric properties of epitaxial Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} thin films grown on GaAs for tunable device application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang Zhibin; Hao Jianhua

2012-09-01

We have epitaxially deposited ferroelectric Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} (BST) thin films grown on GaAs substrate via SrTiO{sub 3} buffer layer by laser molecular beam epitaxy. Structural characteristics of the heterostructure were measured by various techniques. The in-plane dielectric properties of the heteroepitaxial structure under different applying frequency were investigated from -190 to 90 Degree-Sign C, indicating Curie temperature of the BST film to be around 52 Degree-Sign C. At room temperature, the dielectric constant of the heterostructure under moderate dc bias field can be tuned by more than 30% and K factor used for frequency agile materials is foundmore » to be close to 8. Our results offer the possibility to combine frequency agile electronics of ferroelectric titanate with the high-performance microwave capabilities of GaAs for room temperature tunable device application.« less

Low-cost fabrication of highly sensitive room temperature hydrogen sensor based on ordered mesoporous Co-doped TiO2 structure

NASA Astrophysics Data System (ADS)

Li, Zhong; Haidry, Azhar Ali; Wang, Tao; Yao, Zheng Jun

2017-07-01

The development of cost-effective gas sensors with improved sensing properties and minimum power consumption for room temperature hydrogen leakage monitoring is in increasing demand. In this context, this report focus on the facile fabrication of ordered mesoporous TiO2 via evaporation-induced self-assembly route. With the controlled doping threshold (3%Co-TiO2), the output resistance change to 1000 ppm H2 is ˜4.1 × 103 with the response time of 66 s. The sensor response exhibits power law dependence with an increase in the hydrogen concentration, where the power law coefficient was found not only specific to the kind of target gas but also related to temperature. Further, the effect of structure integrity with doping level and humidity on sensing characteristics is interpreted in terms of variation in surface potential eVS and depletion region w caused by the adsorption of molecular oxygen O2-.

Structural and magnetic properties of morphotropic phase boundary involved Tb 1-xGd xFe 2 compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murtaza, Adil; Yang, Sen; Zhou, Chao

2016-09-01

In the present paper, structural, magnetic and magnetostrictive properties of Tb 1-xGd xFe 2 (0 <= x <= 1.0) were studied. Synchrotron x-ray diffraction (XRD) results show the non-cubic symmetry of Tb 1-xGd xFe 2 at room temperature and composition-induced crystallographic phase transition from rhombohedral phase to tetragonal phase. The Gd concentration dependent lattice parameters, lattice distortion and change of easy magnetic direction were detected by synchrotron XRD. With the Gd concentration increases, Curie temperature Tc increases while room temperature magnetization and magnetostriction coefficient lambda(111) and the anisotropy of TbFe 2 decrease. The decrease in spontaneous magnetostriction coefficient lambda(111) withmore » increasing Gd substitution can be understood on the basis of the single-ion model; the corresponding decrease of magnetostriction for Tb 1-xGd xFe 2, and the large magnetostriction value occurs on the Tb-rich side, are ascribed to decrease of lambda(111)« less

Plasticity mechanisms in HfN at elevated and room temperature.

PubMed

Vinson, Katherine; Yu, Xiao-Xiang; De Leon, Nicholas; Weinberger, Christopher R; Thompson, Gregory B

2016-10-06

HfN specimens deformed via four-point bend tests at room temperature and at 2300 °C (~0.7 T m ) showed increased plasticity response with temperature. Dynamic diffraction via transmission electron microscopy (TEM) revealed ⟨110⟩{111} as the primary slip system in both temperature regimes and ⟨110⟩{110} to be a secondary slip system activated at elevated temperature. Dislocation line lengths changed from a primarily linear to a curved morphology with increasing temperature suggestive of increased dislocation mobility being responsible for the brittle to ductile temperature transition. First principle generalized stacking fault energy calculations revealed an intrinsic stacking fault (ISF) along ⟨112⟩{111}, which is the partial dislocation direction for slip on these close packed planes. Though B1 structures, such as NaCl and HfC predominately slip on ⟨110⟩{110}, the ISF here is believed to facilitate slip on the {111} planes for this B1 HfN phase.

Adequacy of solar energy to keep babies warm.

PubMed

Daga, S R; Sequera, D; Goel, S; Desai, B; Gajendragadkar, A

1996-02-01

Solar energy could be used as an alternate energy source for keeping neonates warm especially in tropical countries. The present study investigated the efficacy of solar powered room heating system. Referral center for neonatal care. A fluid system heated by solar panels and circulated into a room was used to maintain room temperature. A servocontrolled heating device was used to regulate and maintain desired room temperature. Neonatal rectal temperature and room temperature. Infants between 1750-2250 g were observed to require a mean room temperature of 32.5 degrees C to maintain normothermia. In 85 infants less than 1500 g, of the 5050 infant temperature records, only 3% showed a record less than 36 degrees C. Solar powered room heating is effective in maintaining infant temperature and is cost-effective as compared to the existing warming devices.

First determination of volume changes and enthalpies of the high-pressure decomposition reaction of the structure H methane hydrate to the cubic structure I methane hydrate and fluid methane.

PubMed

Ogienko, Andrey G; Tkacz, Marek; Manakov, Andrey Yu; Lipkowski, Janusz

2007-11-08

Pressure-temperature (P-T) conditions of the decomposition reaction of the structure H high-pressure methane hydrate to the cubic structure I methane hydrate and fluid methane were studied with a piston-cylinder apparatus at room temperature. For the first time, volume changes accompanying this reaction were determined. With the use of the Clausius-Clapeyron equation the enthalpies of the decomposition reaction of the structure H high-pressure methane hydrate to the cubic structure I methane hydrate and fluid methane have been calculated.

Chemical Reduction of Nd 1.85 Ce 0.15 CuO 4− δ Powders in Supercritical Sodium Ammonia Solutions

DOE PAGES

Dias, Yasmin; Wang, Hui; Zhou, Haiqing; ...

2015-01-01

Nd 1.85 Ce 0.15 CuO 4− δ powders are chemically reduced in supercritical sodium ammonia solutions from room temperature to 350°C. The crystallographic structure of the reduced powders is investigated from Rietveld refinement of X-ray powder diffraction. The atomic positions are maintained constant within experimental errors while temperature factors of all atoms increase significantly after the chemical treatments, especially of Nd/Ce atoms. The ammonothermally reduced Nd 1.85 Ce 0.15 CuO 4− δ powders show diamagnetic below 24 K which is contributed to the lower oxygen content and higher temperature factors of atoms in the treated compound. Themore » ammonothermal method paves a new way to reduce oxides in supercritical solutions near room temperature.« less

Room temperature ferromagnetism and luminescent behavior of Ni doped ZnO nanoparticles prepared by coprecipitation method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arora, Deepawali; Mahajan, Aman; Kaur, Parvinder

2016-05-23

The samples of Zn{sub 1-x}Ni{sub x}O (x= 0.00 and 0.05) were prepared using coprecipitation method and annealed at different temperatures. The effect of Ni ion substitution on the structural and optical properties has been studied using X-ray Diffraction, UV-Visible, Photoluminescence and Magnetic measurements. XRD measurements demonstrate that all the prepared samples are wurtzite polycrystalline single phase in nature, ruling out the presence of any secondary phase formation. Ultraviolet visible measurements showed a decrease in band gap with the increase in annealing temperature and doping concentration. The PL data shows the red shift in all the samples and luminescence quenching withmore » Ni doping. Compared to undoped ZnO, Ni doped ZnO showed room temperature ferromagnetism.« less

Magnetic-field-induced irreversible antiferromagnetic-ferromagnetic phase transition around room temperature in as-cast Sm-Co based SmCo7-xSix alloys

NASA Astrophysics Data System (ADS)

Feng, D. Y.; Zhao, L. Z.; Liu, Z. W.

2016-04-01

A magnetic-field-induced irreversible metamagnetic phase transition from antiferro- to ferromagnetism, which leads to an anomalous initial-magnetization curve lying outside the magnetic hysteresis loop, is reported in arc-melted SmCo7-xSix alloys. The transition temperatures are near room temperature, much higher than other compounds with similar initial curves. Detailed investigation shows that this phenomenon is dependent on temperature, magnetic field and Si content and shows some interesting characteristics. It is suggested that varying interactions between the Sm and Co layers in the crystal are responsible for the formation of a metastable AFM structure, which induces the anomalous phenomenon in as-cast alloys. The random occupation of 3g sites by Si and Co atoms also has an effect on this phenomenon.

Effect of test temperature and strain rate on the tensile properties of high-strength, high-conductivity copper alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zinkle, S.J.; Eatherly, W.S.

1997-04-01

The unirradiated tensile properties of wrought GlidCop AL25 (ITER grade zero, IGO) solutionized and aged CuCrZr, and cold-worked and aged and solutionized and aged Hycon 3HP{trademark} CuNiBe have been measured over the temperature range of 20-500{degrees}C at strain rates between 4 x 10{sup {minus}4} s{sup {minus}1} and 0.06 s{sup {minus}1}. The measured room temperature electrical conductivity ranged from 64 to 90% IACS for the different alloys. All of the alloys were relatively insensitive to strain rate at room temperature, but the strain rate sensitivity of GlidCop Al25 increased significantly with increasing temperature. The CuNiBe alloys exhibited the best combination ofmore » high strength and high conductivity at room temperature. The strength of CuNiBe decreased slowly with increasing temperature. However, the ductility of CuNiBe decreased rapidly with increasing temperature due to localized deformation near grain boundaries, making these alloy heats unsuitable for typical structural applications above 300{degrees}C. The strength and uniform elongation of GlidCop Al25 decreased significantly with increasing temperature at a strain rate of 1 x 10{sup {minus}3} s{sup {minus}1}, whereas the total elongation was independent of test temperature. The strength and ductility of CuCrZr decreased slowly with increasing temperature.« less

Combined Loads Test Fixture for Thermal-Structural Testing Aerospace Vehicle Panel Concepts

NASA Technical Reports Server (NTRS)

Fields, Roger A.; Richards, W. Lance; DeAngelis, Michael V.

2004-01-01

A structural test requirement of the National Aero-Space Plane (NASP) program has resulted in the design, fabrication, and implementation of a combined loads test fixture. Principal requirements for the fixture are testing a 4- by 4-ft hat-stiffened panel with combined axial (either tension or compression) and shear load at temperatures ranging from room temperature to 915 F, keeping the test panel stresses caused by the mechanical loads uniform, and thermal stresses caused by non-uniform panel temperatures minimized. The panel represents the side fuselage skin of an experimental aerospace vehicle, and was produced for the NASP program. A comprehensive mechanical loads test program using the new test fixture has been conducted on this panel from room temperature to 500 F. Measured data have been compared with finite-element analyses predictions, verifying that uniform load distributions were achieved by the fixture. The overall correlation of test data with analysis is excellent. The panel stress distributions and temperature distributions are very uniform and fulfill program requirements. This report provides details of an analytical and experimental validation of the combined loads test fixture. Because of its simple design, this unique test fixture can accommodate panels from a variety of aerospace vehicle designs.

Enhanced room-temperature spin Seebeck effect in a YIG/C60/Pt layered heterostructure

NASA Astrophysics Data System (ADS)

Das, R.; Kalappattil, V.; Geng, R.; Luong, H.; Pham, M.; Nguyen, T.; Liu, Tao; Wu, Mingzhong; Phan, M. H.; Srikanth, H.

2018-05-01

We report on large enhancement of the longitudinal spin Seebeck effect (LSSE) in the Y3Fe5O12 (YIG)/Pt system at room temperature due to the addition of a thin layer of organic semiconductor (C60) in between the YIG and the Pt. LSSE measurements show that the LSSE voltage increases significantly, from the initial value of 150 nV for the YIG/Pt structure to 240 nV for the YIG/C60(5nm)/Pt structure. Radio-frequency transverse susceptibility experiments reveal a significant decrease in the surface perpendicular magnetic anisotropy (PMA) of the YIG film when C60 is deposited on it. These results suggest that the LSSE enhancement may be attributed to increased spin mixing conductance, the decreased PMA, and the large spin diffusion length of C60.

Ferroelectric and paraelectric Ba0.5Sr0.5TiO3 film structure distortions at room temperature and their effects on tunable microwave properties

NASA Astrophysics Data System (ADS)

Alldredge, L. M. B.; Chang, Wontae; Qadri, Syed B.; Kirchoefer, Steven W.; Pond, Jeffrey M.

2007-05-01

Sputter-deposited Ba0.5Sr0.5TiO3 films on (001) MgO were characterized for their dielectric properties with different lattice structures. With varying Ar :O2 ratios during deposition, the films showed either in-plane (ca) tetragonal distortions, significantly affecting the dielectric constant and tunability. The dielectric constant exhibited clear hysteresis with dc bias at room temperature, indicating that the films were ferroelectric. The relationship between the dielectric properties and the distortions was the reverse of that observed in films deposited by pulsed laser deposition. The anisotropic in-plane dielectric behavior can be understood by relating polarization to film distortions and to the presence of permanent dipoles.

Enhanced conformational sampling to visualize a free-energy landscape of protein complex formation

PubMed Central

Iida, Shinji; Nakamura, Haruki; Higo, Junichi

2016-01-01

We introduce various, recently developed, generalized ensemble methods, which are useful to sample various molecular configurations emerging in the process of protein–protein or protein–ligand binding. The methods introduced here are those that have been or will be applied to biomolecular binding, where the biomolecules are treated as flexible molecules expressed by an all-atom model in an explicit solvent. Sampling produces an ensemble of conformations (snapshots) that are thermodynamically probable at room temperature. Then, projection of those conformations to an abstract low-dimensional space generates a free-energy landscape. As an example, we show a landscape of homo-dimer formation of an endothelin-1-like molecule computed using a generalized ensemble method. The lowest free-energy cluster at room temperature coincided precisely with the experimentally determined complex structure. Two minor clusters were also found in the landscape, which were largely different from the native complex form. Although those clusters were isolated at room temperature, with rising temperature a pathway emerged linking the lowest and second-lowest free-energy clusters, and a further temperature increment connected all the clusters. This exemplifies that the generalized ensemble method is a powerful tool for computing the free-energy landscape, by which one can discuss the thermodynamic stability of clusters and the temperature dependence of the cluster networks. PMID:27288028

Structure of nickel-copper alloys subjected to high-pressure torsion to saturation stage

NASA Astrophysics Data System (ADS)

Popov, V. V.; Stolbovsky, A. V.; Popova, E. N.

2017-11-01

Transmission electron microscopy and microhardness measurements were used to study the structure of Ni-Cu alloys subjected to high-pressure torsion (to saturation state) at room-temperature using five revolutions. It was shown that, when passing from copper to nickel, the submicrocrystalline structure becomes substantially refined, and the microhardness increases by more than 1.5 times. This is related to differences in the melting temperature and stacking fault energy. The simultaneous effect of these two factors leads to the nonlinearity of the composition dependences of the crystallite size and microhardness.

On the transmission of terahertz radiation through silicon-based structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Persano, Anna, E-mail: anna.persano@le.imm.cnr.it; Francioso, Luca; Cola, Adriano

2014-07-28

We report on the transmission of a terahertz (THz) radiation through prototype structures based on a p-type silicon substrate. In particular, the bare substrate and progressively more complicated multilayer structures were investigated, allowing to address the effect on the transmission of different factors, such as the orientation of interdigitated contacts with respect to the polarized beam, the temperature, and the current flowing through a conductive SnO{sub 2} nanorods layer. A suitable experimental set-up was developed for the direct spectral measurement of transmission in the range of 0.75–1.1 THz at room and low temperatures. A simple Drude-Lorentz model was formulated, findingmore » a quantitative agreement with the experimental transmission spectrum of the bare substrate at room temperature. For the multilayer structures, the spectra variations observed with temperature are well accounted by the corresponding change of the mobility of holes in the silicon p-type substrate. The influence of the contact orientation is consistent with that of a polarizing metallic grating. Finally, Joule heating effects are observed in the spectra performed as a function of the current flowing through the SnO{sub 2} nanorods layer. The experimental results shown here, together with their theoretical interpretation, provide insights for the development of devices fabricated on conductive substrates aimed to absorb/modulate radiation in the THz range.« less

Leaky electronic states for photovoltaic photodetectors based on asymmetric superlattices

NASA Astrophysics Data System (ADS)

Penello, Germano Maioli; Pereira, Pedro Henrique; Pires, Mauricio Pamplona; Sivco, Deborah; Gmachl, Claire; Souza, Patricia Lustoza

2018-01-01

The concept of leaky electronic states in the continuum is used to achieve room temperature operation of photovoltaic superlattice infrared photodetectors. A structural asymmetric InGaAs/InAlAs potential profile is designed to create states in the continuum with the preferential direction for electron extraction and, consequently, to obtain photovoltaic operation at room temperature. Due to the photovoltaic operation and virtual increase in the bandoffset, the device presents both low dark current and low noise. The Johnson noise limited specific detectivity reaches values as high as 1.4 × 1011 Jones at 80 K. At 300 K, the detectivity obtained is 7.0 × 105 Jones.

Orthorhombic-tetragonal phase coexistence and enhanced piezo-response at room temperature in Zr, Sn, and Hf modified BaTiO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalyani, Ajay Kumar; Brajesh, Kumar; Ranjan, Rajeev, E-mail: rajeev@materials.iisc.ernet.in

2014-06-23

The effect of Zr, Hf, and Sn in BaTiO{sub 3} has been investigated at close composition intervals in the dilute concentration limit. Detailed structural analysis by x-ray and neutron powder diffraction revealed that merely 2 mol. % of Zr, Sn, and Hf stabilizes a coexistence of orthorhombic (Amm2) and tetragonal (P4mm) phases at room temperature. As a consequence, all the three systems show substantial enhancement in the longitudinal piezoelectric coefficient (d{sub 33}), with Sn modification exhibiting the highest value ∼425 pC/N.

First-order martensitic transformation in Heusler-type glass-coated microwires

NASA Astrophysics Data System (ADS)

Zhukov, A.; Ipatov, M.; del Val, J. J.; Taskaev, S.; Churyukanova, M.; Zhukova, V.

2017-12-01

Properly annealed Ni-Mn-Ga glass-covered microwires exhibit a hysteretic anomaly on the temperature dependence of magnetization attributed to the first order martensitic transformation. The temperatures of the structural and magnetic transitions are drastically affected by annealing conditions. Annealed glass-coated Ni-Mn-Ga microwires show a Curie temperature shift close to room temperature. The temperature and magnetic field dependences of magnetization are discussed in terms of atomic disorder, the release of internal stresses, and recrystallization after annealing.

[A surface reacted layer study of titanium-zirconium alloy after dental casting].

PubMed

Zhang, Y; Guo, T; Li, Z; Li, C

2000-10-01

To investigate the influence of the mold temperature on the surface reacted layer of Ti-Zr alloy castings. Ti-Zr alloy was casted into a mold which was made of a zircon (ZrO2.SiO2) for inner coating and a phosphate-bonded material for outer investing with a casting machine (China) designed as vacuum, pressure and centrifuge. At three mold temperatures (room temperature, 300 degrees C, 600 degrees C) the Ti-Zr alloy was casted separately. The surface roughness of the castings was calculated by instrument of smooth finish (China). From the surface to the inner part the Knoop hardness and thickness in reacted layer of Ti-Zr alloy casting was measured. The structure of the surface reacted layer was analysed by SEM. Elemental analyses of the interfacial zone of the casting was made by element line scanning observation. The surface roughness of the castings was increased significantly with the mold temperature increasing. At a higher mold temperature the Knoop hardness of the reactive layer was increased. At the three mold temperature the outmost surface was very hard, and microhardness data decreased rapidly where they reached constant values. The thickness was about 85 microns for castings at room temperature and 300 degrees C, 105 microns for castings at 600 degrees C. From the SEM micrograph of the Ti-Zr alloy casting, the surface reacted layer could be divided into three different layers. The first layer was called non-structure layer, which thickness was about 10 microns for room temperature group, 20 microns for 300 degrees C and 25 microns for 600 degrees C. The second layer was characterized by coarse-grained acicular crystal, which thickness was about 50 microns for three mold temperatures. The third layer was Ti-Zr alloy. The element line scanning showed non-structure layer with higher level of element of O, Al, Si and Zr, The higher the mold temperature during casting, the deeper the Si permeating and in the second layer the element Si could also be found. The mold temperature is one of the major factors influencing to casting quality. In order to reduce the surface reacted layer of Ti-Zr alloy castings, the lower mold temperature and the investment without Si should be chosen.

Gradient structure-induced temperature responsiveness in styrene/methyl methacrylate gradient copolymers micelles.

PubMed

Zheng, Chao; Huang, Haiying; He, Tianbai

2014-02-01

In this work, micelles are formed by gradient copolymer of styrene and methyl methacrylate in acetone-water mixture and their temperature responsiveness is investigated in a narrow range near room temperature. Three different kinds of structural transitions could be induced by temperature: unimers to micelle transition, shrinkage/stretching of micelles, and morphological transition from spherical micelles to vesicles. In addition, a model analysis on the interface of gradient copolymer micelle is made to better understand these phenomena. It is found that both position and composition of the interface could alter in response to the change in temperature. According to the experiments and model analysis, it is proposed that temperature responsiveness might be an intrinsic and universal property of gradient copolymer micelles, which only originates from the gradient structure. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Relaxor ferroelectricity and electric-field-driven structural transformation in the giant lead-free piezoelectric (Ba ,Ca ) (Ti ,Zr ) O3

NASA Astrophysics Data System (ADS)

Brajesh, Kumar; Tanwar, Khagesh; Abebe, Mulualem; Ranjan, Rajeev

2015-12-01

There is great interest in lead-free (B a0.85C a0.15 ) (T i0.90Z r0.10 ) O3 (15/10BCTZ) because of its exceptionally large piezoelectric response [Liu and Ren, Phys. Rev. Lett. 103, 257602 (2009), 10.1103/PhysRevLett.103.257602]. In this paper, we have analyzed the nature of: (i) crystallographic phase coexistence at room temperature, (ii) temperature- and field-induced phase transformation to throw light on the atomistic mechanisms associated with the large piezoelectric response of this system. A detailed temperature-dependent dielectric and lattice thermal expansion study proved that the system exhibits a weak dielectric relaxation, characteristic of a relaxor ferroelectric material on the verge of exhibiting a normal ferroelectric-paraelectric transformation. Careful structural analysis revealed that a ferroelectric state at room temperature is composed of three phase coexistences, tetragonal (P 4 m m )+ orthorhombic(Amm 2 )+rhombohedral(R 3 m ) . We also demonstrate that the giant piezoresponse is associated with a significant fraction of the tetragonal phase transforming to rhombohedral. It is argued that the polar nanoregions associated with relaxor ferroelectricity amplify the piezoresponse by providing an additional degree of intrinsic structural inhomogeneity to the system.

Influence of load and temperature on tribological behaviour of electroless Ni-P deposits

NASA Astrophysics Data System (ADS)

Kundu, S.; Das, S. K.; Sahoo, P.

2016-09-01

Electroless Ni-P coatings have shown tremendous potential as tribology material at room temperature. However, the performance of the same in high temperature field needs to be evaluated as investigation reveals the softening of most of the coating materials. In the current study, both as-deposited as well as heat treated samples are developed for the performance evaluation. Coatings are tested under different loads with a constant speed and at temperatures ranging from room temperature (R.T.) to 500°C. Tribological tests are carried out on a pin-on- disc tribotester by selecting a wear track diameter of 60 mm for 5 minutes. Wear is reported in the form of wear rate by following Archard's equation. The microstructure characterization of the coating is performed using SEM (Scanning Electron Microscopy), EDX (Energy Dispersive X-Ray Analysis) and XRD (X-Ray Diffraction Analysis). Coating is developed with phosphorous weight percentages around 9% on cylindrical mild steel samples and the deposition thickness is observed to be around 50 μm. The as-deposited coating is found to be amorphous in nature and hardness of the as-deposited coating is found to be around 585HV01. Friction coefficient increases initially with the increase in temperature from room temperature up to 100°C but thereafter gradually decrease with the increase in temperature. Initial increase in temperature (up to 100°C) provides higher rate of wear compared to room temperature but with further increase it drops in most of the cases. Wear rate increases with the increase in temperature but as it crosses or nears the phase transformation temperature (around 340°C), the scenario gets reversed. From X-ray diffraction analysis, it is found that coating is amorphous in as-deposited condition but transforms into a crystalline structure with heat treatment.

Structural tunability and switchable exciton emission in inorganic-organic hybrids with mixed halides

NASA Astrophysics Data System (ADS)

Ahmad, Shahab; Baumberg, Jeremy J.; Vijaya Prakash, G.

2013-12-01

Room-temperature tunable excitonic photoluminescence is demonstrated in alloy-tuned layered Inorganic-Organic (IO) hybrids, (C12H25NH3)2PbI4(1-y)Br4y (y = 0 to 1). These perovskite IO hybrids adopt structures with alternating stacks of low-dimensional inorganic and organic layers, considered to be naturally self-assembled multiple quantum wells. These systems resemble stacked monolayer 2D semiconductors since no interlayer coupling exists. Thin films of IO hybrids exhibit sharp and strong photoluminescence (PL) at room-temperature due to stable excitons formed within the low-dimensional inorganic layers. Systematic variation in the observed exciton PL from 510 nm to 350 nm as the alloy composition is changed, is attributed to the structural readjustment of crystal packing upon increase of the Br content in the Pb-I inorganic network. The energy separation between exciton absorption and PL is attributed to the modified exciton density of states and diffusion of excitons from relatively higher energy states corresponding to bromine rich sites towards the lower energy iodine sites. Apart from compositional fluctuations, these excitons show remarkable reversible flips at temperature-induced phase transitions. All the results are successfully correlated with thermal and structural studies. Such structural engineering flexibility in these hybrids allows selective tuning of desirable exciton properties within suitable operating temperature ranges. Such wide-range PL tunability and reversible exciton switching in these novel IO hybrids paves the way to potential applications in new generation of optoelectronic devices.

Effect of rapid thermal annealing on the structural and electrical properties of RF sputtered CCTO thin film

NASA Astrophysics Data System (ADS)

Tripathy, N.; Das, K. C.; Ghosh, S. P.; Bose, G.; Kar, J. P.

2017-02-01

CaCu3Ti4O12 (CCTO) thin films have been deposited by RF magnetron sputtering on silicon substrates at room temperature. As-deposited thin films were subjected to rapid thermal annealing (RTA) at different temperatures ranging from 850°C to 1000°C. XRD and capacitance - voltage studies indicate that the structural and electrical properties of CCTO thin film strongly depend upon the annealing temperature. XRD pattern of CCTO thin film annealed at 950°C revealed the polycrystalline nature with evolutions of microstructures. Electrical properties of the dielectric films were investigated by fabricating Al/CCTO/Si metal oxide semiconductor structure. Electrical properties were found to be deteriorated with increasing in annealing temperature.

Nonlinear absorption in AlGaAs/GaAs multiple quantum well structures grown by metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Lee, H. C.; Hariz, A.; Dapkus, P. D.; Kost, A.; Kawase, M.

1987-01-01

This paper reports the study of growth conditions for achieving the sharp exciton resonances and low-intensity saturation of these resonances in AlGaAs-GaAs multiple quantum well structures grown by metalorganic chemical vapor deposition. Low growth temperature is necessary to observe this sharp resonance feature at room temperature. The optimal growth conditions are a tradeoff between the high temperatures required for high quality AlGaAs and low temperatures required for high-purity GaAs. A strong optical saturation of the excitonic absorption has been observed. A saturation density as low as 250 W/sq cm is reported.

Structural characterization and physicochemical features of new hybrid compound containing chlorate anions of cadmate (II)

NASA Astrophysics Data System (ADS)

Lassoued, Mohamed Saber; Abdelbaky, Mohammed S. M.; Lassoued, Abdelmajid; Gadri, Abdellatif; Ammar, Salah; Ben Salah, Abdelhamid; García-Granda, Santiago

2017-08-01

The present paper reports the synthesis of a single crystal of a new organic-inorganic hybrid compound, with the formula (C6H14N2) CdCl4·H2O, by slow evaporation method at room temperature. It was characterized by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), Hirshfeld surface, spectroscopy measurement, thermal study and photoluminescence (PL) properties. A preliminary SCXRD structural analysis revealed that it crystallized in the monoclinic system (space group P21/c) with the following unit cell parameters: a = 12.95823(16) Å, b = 14.92449(16) Å, c = 7.13838(9) Å and β = 103.2108(12)° with Z = 4. The refinement converged to R = 0.0164 and ωR = 0.0393. Its atomic arrangement can be described as an alternation of organic and inorganic layers along the a-axis. The crystal packing was governed by the N-H⋯Cl and O-H⋯Cl hydrogen bonding interaction between the 1.2-diammoniumcyclohexane cations, the [CdCl42n-]n anions and water molecule. The Hirshfeld surface analysis was conducted to investigate intermolecular interactions and associated 2D fingerprint plots, revealing the relative contribution of these interactions in the crystal structure quantitatively. Furthermore, the room temperature infrared (IR) spectrum of the title compound was recorded and analyzed on the basis of data found in the literature. Besides, the thermal analysis studies were performed, but no phase transition was found in the temperature range between 30 and 450 °C. The optical and PL properties of the compound were investigated in the solid state at room temperature and exhibited three bands at 225, 268 and 315 nm and a strong fluorescence at 443 nm.

Real-time modeling of heat distributions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamann, Hendrik F.; Li, Hongfei; Yarlanki, Srinivas

Techniques for real-time modeling temperature distributions based on streaming sensor data are provided. In one aspect, a method for creating a three-dimensional temperature distribution model for a room having a floor and a ceiling is provided. The method includes the following steps. A ceiling temperature distribution in the room is determined. A floor temperature distribution in the room is determined. An interpolation between the ceiling temperature distribution and the floor temperature distribution is used to obtain the three-dimensional temperature distribution model for the room.

The effect of moisture on the dynamic thermomechanical properties of a graphite/epoxy composite

NASA Technical Reports Server (NTRS)

Sykes, G. F.; Burks, H. D.; Nelson, J. B.

1977-01-01

A study has been made of the effect of moisture absorption on the dynamic thermomechanical properties of a graphite/epoxy composite recently considered for building primary aircraft structures. Torsional braid analysis (TBA) and thermomechanical analysis (TMA) techniques were used to measure changes in the glass transition temperature (Tg) and the initial softening temperature (heat distortion temperature, HDT) of T-300/5209 graphite/epoxy composites exposed to room temperature water soak.

Castable and High Modulus Acoustic Dampening Material

DTIC Science & Technology

2007-02-22

high impact strength and high dampening laminate structures (e.g., fiberglass parts, etc.). It appears that a carboxy-terminated butadiene nitrile ( CTBN ...Sanjana reference also states that the preferred glass transition temperature for the CTBNs is "<-200". The greater the difference from room...temperature (or the temperature of interest) that the glass transition of the CTBN is, the less acoustic or vibrational energy will be absorbed/dampened

Methods for structural design at elevated temperatures

NASA Technical Reports Server (NTRS)

Ellison, A. M.; Jones, W. E., Jr.; Leimbach, K. R.

1973-01-01

A procedure which can be used to design elevated temperature structures is discussed. The desired goal is to have the same confidence in the structural integrity at elevated temperature as the factor of safety gives on mechanical loads at room temperature. Methods of design and analysis for creep, creep rupture, and creep buckling are presented. Example problems are included to illustrate the analytical methods. Creep data for some common structural materials are presented. Appendix B is description, user's manual, and listing for the creep analysis program. The program predicts time to a given creep or to creep rupture for a material subjected to a specified stress-temperature-time spectrum. Fatigue at elevated temperature is discussed. Methods of analysis for high stress-low cycle fatigue, fatigue below the creep range, and fatigue in the creep range are included. The interaction of thermal fatigue and mechanical loads is considered, and a detailed approach to fatigue analysis is given for structures operating below the creep range.

Structure and Properties of Silica Glass Densified in Cold Compression and Hot Compression

NASA Astrophysics Data System (ADS)

Guerette, Michael; Ackerson, Michael R.; Thomas, Jay; Yuan, Fenglin; Bruce Watson, E.; Walker, David; Huang, Liping

2015-10-01

Silica glass has been shown in numerous studies to possess significant capacity for permanent densification under pressure at different temperatures to form high density amorphous (HDA) silica. However, it is unknown to what extent the processes leading to irreversible densification of silica glass in cold-compression at room temperature and in hot-compression (e.g., near glass transition temperature) are common in nature. In this work, a hot-compression technique was used to quench silica glass from high temperature (1100 °C) and high pressure (up to 8 GPa) conditions, which leads to density increase of ~25% and Young’s modulus increase of ~71% relative to that of pristine silica glass at ambient conditions. Our experiments and molecular dynamics (MD) simulations provide solid evidences that the intermediate-range order of the hot-compressed HDA silica is distinct from that of the counterpart cold-compressed at room temperature. This explains the much higher thermal and mechanical stability of the former than the latter upon heating and compression as revealed in our in-situ Brillouin light scattering (BLS) experiments. Our studies demonstrate the limitation of the resulting density as a structural indicator of polyamorphism, and point out the importance of temperature during compression in order to fundamentally understand HDA silica.

Time-dependent local and average structural evolution of δ-phase 239Pu-Ga alloys

DOE PAGES

Smith, Alice I.; Page, Katharine L.; Siewenie, Joan E.; ...

2016-08-05

Here, plutonium metal is a very unusual element, exhibiting six allotropes at ambient pressure, between room temperature and its melting point, a complicated phase diagram, and a complex electronic structure. Many phases of plutonium metal are unstable with changes in temperature, pressure, chemical additions, or time. This strongly affects structure and properties, and becomes of high importance, particularly when considering effects on structural integrity over long periods of time [1]. This paper presents a time-dependent neutron total scattering study of the local and average structure of naturally aging δ-phase 239Pu-Ga alloys, together with preliminary results on neutron tomography characterization.

Optical detection of symmetric and antisymmetric states in double quantum wells at room temperature

NASA Astrophysics Data System (ADS)

Marchewka, M.; Sheregii, E. M.; Tralle, I.; Marcelli, A.; Piccinini, M.; Cebulski, J.

2009-09-01

We studied the optical reflectivity of a specially grown double quantum well (DQW) structure characterized by a rectangular shape and a high electron density at room temperature. Assuming that the QWs depth is known, reflectivity spectra in the mid-IR range allow to carry out the precise measurements of the SAS-gap values (the energy gap between the symmetric and anti-symmetric states) and the absolute energies of both symmetric and antisymmetric electron states. The results of our experiments are in favor of the existence of the SAS splitting in the DQWs at room temperature. Here we have shown that the SAS gap increases proportionally to the subband quantum number and the optical electron transitions between symmetric and antisymmetric states belonging to different subbands are allowed. These results were used for interpretation of the beating effect in the Shubnikov-de Haas (SdH) oscillations at low temperatures (0.6 and 4.2 K). The approach to the calculation of the Landau-levels energies for DQW structures developed earlier [D. Ploch , Phys. Rev. B 79, 195434 (2009)] is used for the analysis and interpretation of the experimental data related to the beating effect. We also argue that in order to explain the beating effect in the SdH oscillations, one should introduce two different quasi-Fermi levels characterizing the two electron subsystems regarding symmetry properties of their wave functions, symmetric and antisymmetric ones. These states are not mixed neither by electron-electron interaction nor probably by electron-phonon interaction.

Synthesis and characterization of structural, morphological and photosensor properties of Cu0.1Zn0.9S thin film prepared by a facile chemical method

NASA Astrophysics Data System (ADS)

Gubari, Ghamdan M. M.; Ibrahim Mohammed S., M.; Huse, Nanasaheb P.; Dive, Avinash S.; Sharma, Ramphal

2018-05-01

The Cu0.1Zn0.9S thin film was grown by facile chemical bath deposition (CBD) method on glass substrates at 60°C. The structural, morphological, photosensor properties of the as-grown thin film has been investigated. The structural and phase confirmation of the as-grown thin film was carried out by X-ray diffraction (XRD) technique and Raman spectroscopy. The FE-SEM images showed that the thin films are well covered with material on an entire glass substrate. From the optical absorption spectrum, the direct band gap energy for the Cu0.1Zn0.9S thin film was found to be ˜3.16 eV at room temperature. The electrical properties were measured at room temperature in the voltage range ±2.5 V, showed a drastic enhancement in current under light illumination with the highest photosensitivity of ˜72 % for 260 W.

Observation of stable Néel skyrmions in cobalt/palladium multilayers with Lorentz transmission electron microscopy

DOE PAGES

Pollard, Shawn D.; Garlow, Joseph A.; Yu, Jiawei; ...

2017-03-10

Néel skyrmions are of high interest due to their potential applications in a variety of spintronic devices, currently accessible in ultrathin heavy metal/ferromagnetic bilayers and multilayers with a strong Dzyaloshinskii–Moriya interaction. Here in this paper we report on the direct imaging of chiral spin structures including skyrmions in an exchange-coupled cobalt/palladium multilayer at room temperature with Lorentz transmission electron microscopy, a high-resolution technique previously suggested to exhibit no Néel skyrmion contrast. Phase retrieval methods allow us to map the internal spin structure of the skyrmion core, identifying a 25 nm central region of uniform magnetization followed by a larger regionmore » characterized by rotation from in- to out-of-plane. The formation and resolution of the internal spin structure of room temperature skyrmions without a stabilizing out-of-plane field in thick magnetic multilayers opens up a new set of tools and materials to study the physics and device applications associated with chiral ordering and skyrmions.« less

[Synthesis and spectral characteristic of Ga-Fe3O4 at room temperature].

PubMed

Wang, Jing; Deng, Tong; Yang, Cai-Qin; Lin, Yu-Long; Wang, Wei; Wu, Hai-Yan

2008-03-01

Gallium bearing ferrites with different gallium content were synthesized by oxidation of ferrous and gallium ions under alkaline condition and room temperature. The samples were subjected to IR, XRD, Mossbauer spectral analysis and magnetization characterization. The results indicated that the green-rust intermediate phase would be produced during the procedure of Ga-Fe3O4 formation, and the green-rust intermediate phase was converted to ferrites with spinel structure during the drying under hot-N2 atmosphere. With the introduction of gallium into the spinel structure, the interplanar crystal spacing of the spinel structure decreased, as indicated from XRD spectra, and the lattice vibration of M(T)-O-M(o) moved to the high-frequency resulting from IR spectra. A small amount gallium introduction entered the tetrahedral sites preferentially rather than the octahedral sites, and increasing gallium introduction would enhance the occupation of octahedral sites. Furthermore, a small content of gallium in the initial solution could prevent the formation of non-magnetic Fe2O3.

Some physical properties of Nb2O5 thin films prepared using nobic acid based colloidal suspension at room temperature

NASA Astrophysics Data System (ADS)

Salim, Evan T.; Admon Saimon, Jehan; Abood, Marwa K.; Fakhri, Makram A.

2017-10-01

This work presents the successful preparation of niobium pentoxide micro structures thin films at room temperature. A chemical colloidal suspension was deposited employing Spin coating method. Nb2O5 thin films were prepared at two different thicknesses before and after ultrasonic vibration processes. Optical, structural, and morphological properties were studied. An enhanced crystalline structure with bigger grain size at both thicknesses was obtained after ultrasonic process; this was ensured by SEM results. The energy gap of the prepared films was estimated and found to be about (2.81, 2.42) eV for (T1  =  325 nm) and (2.59, 2.32) eV at the second thickness (T2  =  425 nm). The I-V characteristic study of prepared heterojunction on silicon substrate show an increase in the rectification ratio after the ultrasonic vibrational process for both thicknesses.

Structure of free radicals in irradiated acetyl-L-leucine single crystals at 77 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Almanov, G.A.; Bogdanchikov, G.A.; Usov, O.M.

1988-09-01

By using the EPR method, two types of radicals are observed, which are formed in acetyl-L-leucine single crystals irradiated at 77K. These are alkyl type radicals (CH/sub 3/)/sub 2/CCH/sub 2/CH(NHCOCH/sub 3/)COOH and peptide group radicals. When the crystals are defrozen to room temperatures, the radicals of the second type disappear without formation of paramagnetic particles. Two possible structures of the peptide group radicals were studied by the INDO method. On defreezing to room temperature, the alkyl group radical is retained, while the peptide radical disappears without formation of paramagnetic particles. For the protonated form of the anion-radical, a better agreementmore » is observed between the theoretically calculated and the experimentally obtained HFI constants. The quantum chemical analysis of the possible structures of the peptide group radicals indicates that the formation of the protonated form of the anion-radical is energetically favorable.« less

The influence of room temperature on Mg isotope measurements by MC-ICP-MS.

PubMed

Zhang, Xing-Chao; Zhang, An-Yu; Zhang, Zhao-Feng; Huang, Fang; Yu, Hui-Min

2018-03-24

We observed that the accuracy and precision of magnesium (Mg) isotope analyses could be affected if the room temperature oscillated during measurements. To achieve high quality Mg isotopic data, it is critical to evaluate how the unstable room temperature affects Mg isotope measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). We measured the Mg isotopes for the reference material DSM-3 using MC-ICP-MS under oscillating room temperatures in spring. For a comparison, we also measured the Mg isotopes under stable room temperatures, which was achieved by the installation of an improved temperature control system in the laboratory. The δ 26 Mg values measured under oscillating room temperatures have a larger deviation (δ 26 Mg from -0.09 to 0.08‰, with average δ 26 Mg = 0.00 ± 0.08 ‰) than those measured under a stable room temperature (δ 26 Mg from -0.03 to 0.03‰, with average δ 26 Mg = 0.00 ± 0.02 ‰) using the same MC-ICP-MS system. The room temperature variation can influence the stability of MC-ICP-MS. Therefore, it is critical to keep the room temperature stable to acquire high precise and accurate isotopic data when using MC-ICP-MS, especially when using the sample-standard bracketing (SSB) correction method. This article is protected by copyright. All rights reserved.

High-Temperature Thermoelectric Properties of Perovskite-Type Pr0.9Sr0.1Mn1- x Fe x O3 (0 ≤ x ≤ 1)

NASA Astrophysics Data System (ADS)

Nakatsugawa, H.; Saito, M.; Okamoto, Y.

2017-05-01

Polycrystalline samples of Pr0.9Sr0.1Mn1- x Fe x O3 (0 ≤ x ≤ 1) have been synthesized using a conventional solid-state reaction method, and the crystal structure studied at room temperature. The magnetic susceptibility was measured from 5 K to 350 K. The electrical resistivity, Seebeck coefficient, and thermal conductivity were investigated as functions of temperature below 850 K. For all samples, the perovskite structure at room temperature exhibited orthorhombic Pbnm phase. While the Pr0.9Sr0.1MnO3 ( x = 0) sample exhibited ferromagnetic-like ground state below T C = 145 K (Curie temperature), the ferromagnetic transition temperature T C decreased with increasing x. The Seebeck coefficient of the samples with 0 ≤ x ≤ 0.8 decreased with increasing temperature because of double-exchange interaction of Mn ions. In fact, the carrier type for x = 0 changed from hole-like to electron-like behavior above 800 K. On the other hand, the samples with x ≥ 0.9 showed large positive Seebeck coefficient over the entire temperature range, indicating that the low-spin state of Fe ions dominated the electronic structure for this x range. In particular, the sample with x = 1 exhibited p-type thermoelectric properties with relatively high Seebeck coefficient, moderate electrical resistivity, and low thermal conductivity. Thus, the sample with x = 1 showed power factor of 20 μW m-1 K-2 at 850 K leading to ZT of 0.024 at this temperature, indicating that hole-doped perovskite-type iron oxide is a good candidate high-temperature thermoelectric p-type oxide.

Structural and magnetic phase transitions in gadolinium under high pressures and low temperatures

NASA Astrophysics Data System (ADS)

Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

2014-10-01

High pressure structural transition studies have been carried out on rare earth metal gadolinium in a diamond anvil cell at room temperature to 169 GPa. Gadolinium has been compressed to 38% of its initial volume at this pressure. With increasing pressure, a crystal structure sequence of hcp → Sm-type → dhcp → fcc → dfcc → monoclinic has been observed in our studies on gadolinium. The measured equation of state of gadolinium is presented to 169 GPa at ambient temperature. Magnetic ordering temperature of gadolinium has been studied using designer diamond anvils to a pressure of 25 GPa and a temperature of 10 K. The magnetic ordering temperature has been determined from the four-point electrical resistivity measurements carried out on gadolinium. Our experiments show that the magnetic transition temperature decreases with increasing pressure to 19 GPa and then increases when gadolinium is subjected to higher pressures.

Structural relaxation driven increase in elastic modulus for a bulk metallic glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arora, Harpreet Singh; Aditya, Ayyagari V.; Mukherjee, Sundeep, E-mail: sundeep.mukherjee@unt.edu

2015-01-07

The change in elastic modulus as a function of temperature was investigated for a zirconium-based bulk metallic glass. High temperature nano-indentation was done over a wide temperature range from room temperature to the glass-transition. At higher temperature, there was a transition from inhomogeneous to homogeneous deformation, with a decrease in serrated flow and an increase in creep displacement. Hardness was found to decrease, whereas elastic modulus was found to increase with temperature. The increase in elastic modulus for metallic glass at higher temperature was explained by diffusive rearrangement of atoms resulting in free volume annihilation. This is in contrast tomore » elastic modulus increase with temperature for silicate glasses due to compaction of its open three dimensional coordinated structure without any atomic diffusion.« less

Temperature and pressure effects on GFP mutants: explaining spectral changes by molecular dynamics simulations and TD-DFT calculations.

PubMed

Jacchetti, Emanuela; Gabellieri, Edi; Cioni, Patrizia; Bizzarri, Ranieri; Nifosì, Riccardo

2016-05-14

By combining spectroscopic measurements under high pressure with molecular dynamics simulations and quantum mechanics calculations we investigate how sub-angstrom structural perturbations are able to tune protein function. We monitored the variations in fluorescence output of two green fluorescent protein mutants (termed Mut2 and Mut2Y, the latter containing the key T203Y mutation) subjected to pressures up to 600 MPa, at various temperatures in the 280-320 K range. By performing 150 ns molecular dynamics simulations of the protein structures at various pressures, we evidenced subtle changes in conformation and dynamics around the light-absorbing chromophore. Such changes explain the measured spectral tuning in the case of the sizable 120 cm(-1) red-shift observed for pressurized Mut2Y, but absent in Mut2. Previous work [Barstow et al., Proc. Natl. Acad. Sci. U. S. A., 2008, 105, 13362] on pressure effects on GFP also involved a T203Y mutant. On the basis of cryocooling X-ray crystallography, the pressure-induced fluorescence blue shift at low temperature (77 K) was attributed to key changes in relative conformation of the chromophore and Tyr203 phenol ring. At room temperature, however, a red shift was observed at high pressure, analogous to the one we observe in Mut2Y. Our investigation of structural variations in compressed Mut2Y also explains their result, bridging the gap between low-temperature and room-temperature high-pressure effects.

Application of TlBr to nuclear medicine imaging

NASA Astrophysics Data System (ADS)

Cirignano, Leonard; Kim, Hadong; Kargar, Alireza; Churilov, Alexei V.; Ciampi, Guido; Higgins, William; Kim, Suyoung; Barber, Bradford; Haston, Kyle; Shah, Kanai

2012-10-01

Thallium bromide (TlBr) has been under development for room temperature gamma ray spectroscopy due to high density, high Z and wide bandgap of the material. Furthermore, its low melting point (460 °C), cubic crystal structure and congruent melting with no solid-solid phase transitions between the melting point and room temperature, TlBr can be grown by relatively simple melt based methods. As a result of improvements in material processing and detector fabrication over the last several years, TlBr with electron mobility-lifetime products (μeτe) in the mid 10-3 cm2/V range has been obtained. In this paper we are going to report on our unipolar charging TlBr results for the application as a small animal imaging. For SPECT application, about 5 mm thick pixellated detectors were fabricated and tested. About 1 % FWHM at 662 keV energy resolution was estimated at room temperature. By applying the depth correction technique, less than 1 % energy resolution was estimated. We are going to report the results from orthogonal strip TlBr detector for PET application. In this paper we also present our latest detector highlights and recent progress made in long term stability of TlBr detectors at or near room temperature. This work is being supported by the Domestic Nuclear Detection Office (DNDO) and the Department of Energy (DOE).

Heterogeneity in a room-temperature ionic liquid: persistent local environments and the red-edge effect.

PubMed

Hu, Zhonghan; Margulis, Claudio J

2006-01-24

In this work, we investigate the slow dynamics of 1-butyl-3-methylimidazolium hexafluorophosphate, a very popular room-temperature ionic solvent. Our study predicts the existence of heterogeneity in the liquid and shows that this heterogeneity is the underlying microscopic cause for the recently reported "red-edge effect" (REE) observed in the study of fluorescence of the organic probe 2-amino-7-nitrofluorene. This theoretical work explains in microscopic terms the relation between REE and dynamic heterogeneity in a room-temperature ionic liquid (IL). The REE is typical of micellar or colloidal systems, which are characterized by microscopic environments that are structurally very different. In contrast, in the case of this room-temperature IL, the REE occurs because of the long period during which molecules are trapped in quasistatic local solvent cages. This trapping time, which is longer than the lifetime of the excited-state probe, together with the inability of the surroundings to adiabatically relax, induces a set of site-specific spectroscopic responses. Subensembles of fluorescent molecules associated with particular local environments absorb and emit at different frequencies. We describe in detail the absorption wavelength-dependent emission spectra of 2-amino-7-nitrofluorene and show that this dependence on lambda(ex) is characteristic of the IL and, as is to be expected, is absent in the case of a normal solvent such as methanol.

Investigation of room temperature ferromagnetic nanoparticles of Gd 5Si 4

DOE PAGES

Hadimani, R. L.; Gupta, S.; Harstad, S. M.; ...

2015-07-06

Gd 5(Si xGe 1-x) 4 compounds undergo first-order phase transitions close to room temperature when x ~ = 0.5, which are accompanied by extreme changes of properties. We report the fabrication of the nanoparticles of one of the parent compounds-Gd 5Si 4-using high-energy ball milling. Crystal structure, microstructure, and magnetic properties have been investigated. Particles agglomerate at long milling times, and the particles that are milled >20 min lose crystallinity and no longer undergo magnetic phase transition close to 340 K, which is present in a bulk material. The samples milled for >20 min exhibit a slightly increased coercivity. Asmore » a result, magnetization at a high temperature of 275K decreases with the increase in the milling time.« less

A fabrication and characterictics of microbolometer detectors using VOx/ZnO/VOx multilayer thin film processing

NASA Astrophysics Data System (ADS)

Han, Myung-Soo; Kim, Dae Hyeon; Ko, Hang Ju; Shin, Jae Chul; Kim, Hyo Jin; Kim, Do Gun

2014-06-01

In this work, a novel fabrication method for VOx-ZnO multilayers with mixed phase of the VO2 and V2O3 through the diffusion of oxygen by annealing at low temperature is presented. A stable sandwich structure of a VOx/ZnO/VOx multilayer was deposited at room temperature, through the oxygen gas flow rate, by RF sputtering system, and the mixed phase was formed through oxygen diffusion by annealing at O2 atmosphere. The results show that the single phase like multilayer formed by this process has a high TCR of more than -2.5%/K and low resistance of about 100 kohm at room temperature. XRD results for the as-deposited VOx/ZnO/VOx multilayer.

Size-Dependent Brittle-to-Ductile Transition in Silica Glass Nanofibers.

PubMed

Luo, Junhang; Wang, Jiangwei; Bitzek, Erik; Huang, Jian Yu; Zheng, He; Tong, Limin; Yang, Qing; Li, Ju; Mao, Scott X

2016-01-13

Silica (SiO2) glass, an essential material in human civilization, possesses excellent formability near its glass-transition temperature (Tg > 1100 °C). However, bulk SiO2 glass is very brittle at room temperature. Here we show a surprising brittle-to-ductile transition of SiO2 glass nanofibers at room temperature as its diameter reduces below 18 nm, accompanied by ultrahigh fracture strength. Large tensile plastic elongation up to 18% can be achieved at low strain rate. The unexpected ductility is due to a free surface affected zone in the nanofibers, with enhanced ionic mobility compared to the bulk that improves ductility by producing more bond-switching events per irreversible bond loss under tensile stress. Our discovery is fundamentally important for understanding the damage tolerance of small-scale amorphous structures.

Extreme low thermal conductivity in nanoscale 3D Si phononic crystal with spherical pores.

PubMed

Yang, Lina; Yang, Nuo; Li, Baowen

2014-01-01

In this work, we propose a nanoscale three-dimensional (3D) Si phononic crystal (PnC) with spherical pores, which can reduce the thermal conductivity of bulk Si by a factor up to 10,000 times at room temperature. Thermal conductivity of Si PnCs depends on the porosity, for example, the thermal conductivity of Si PnCs with porosity 50% is 300 times smaller than that of bulk Si. The phonon participation ratio spectra demonstrate that more phonons are localized as the porosity increases. The thermal conductivity is insensitive to the temperature changes from room temperature to 1100 K. The extreme-low thermal conductivity could lead to a larger value of ZT than unity as the periodic structure affects very little the electric conductivity.

Promising thermoelectric properties of phosphorenes.

PubMed

Sevik, Cem; Sevinçli, Hâldun

2016-09-02

Electronic, phononic, and thermoelectric transport properties of single layer black- and blue-phosphorene structures are investigated with first-principles based ballistic electron and phonon transport calculations employing hybrid functionals. The maximum values of room temperature thermoelectric figure of merit, ZT corresponding to armchair and zigzag directions of black-phosphorene, ∼0.5 and ∼0.25, are calculated as rather smaller than those obtained with first-principles based semiclassical Boltzmann transport theory calculations. On the other hand, the maximum value of room temperature ZT of blue-phosphorene is predicted to be substantially high and remarkable values as high as 2.5 are obtained for elevated temperatures. Besides the fact that these figures are obtained at the ballistic limit, our findings mark the strong possibility of high thermoelectric performance of blue-phosphorene in new generation thermoelectric applications.

Magnetic properties of Zn0.9(Mn0.05,Ni0.05)O nanoparticle: Experimental and theoretical investigation

NASA Astrophysics Data System (ADS)

Mounkachi, O.; Lakhal, M.; Labrim, H.; Hamedoun, M.; Benyoussef, A.; El Kenz, A.; Loulidi, M.; Bhihi, M.

2012-06-01

The crystalline and magnetic properties of 5% Mn and 5% Ni co-doped nanocrystalline ZnO particles, obtained by the co-precipitation method, are performed. X-ray diffraction data revealed that Zn0.90Mn0.05Ni0.05O crystallizes in the monophasic wurtzite structure. DC magnetization measurement showed that the samples are paramagnetic at room temperature. However, a large increase in the magnetization is observed below 50 K. This behavior, along with the negative value of Weiss constant obtained from the linear fit of magnetic susceptibility data below room temperature, indicates ferrimagnetic behavior. The ferrimagnetic properties observed at low temperature are explained and confirmed from ab-initio calculations using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation.

Room temperature deposition of gold onto the diffuse and sharp diffraction spot Si(111)-( 3 × 3) R30° Au surfaces

NASA Astrophysics Data System (ADS)

Plass, Richard; Marks, Laurence D.

1996-06-01

Room temperature gold depositions onto Si(111)-( 3 × 3) R30° Au surfaces with diffuse and sharp diffraction spots [Surf. Sci. 242 (1991) 73] (diffuse and sharp 3 × 3 Au hereafter) under UHV conditions has been monitored using transmission electron diffraction (TED). Both systems display an increase in surface structure diffraction spot intensities up to the completion of 1.0 monolayer (ML) after which the surface beams display an exponential decrease in intensity with coverage. The exponential decay rate decreases after roughly 1.33 ML. These results can be attributed to gold initially diffusing to and filling 3 × 3 Au gold trimer sites in vacancy type surface domain walls [Surf. Sci. 342 (1995) 233], then filling one of three possible sites on the 3 × 3 Au structure with essentially no surface diffusion, disrupting nearby gold trimers. Gold deposition onto the diffuse type structure caused the formation and expansion of satellite arcs around the strongest 3 × 3 beams similar to those seen by others [Surf. Sci. 242 (1991) 73; Jpn. J. Appl. Phys. 16 (1977) 891; J. Vac. Sci. Technol. A 10 (1992) 3486] at elevated temperatures while the sharp structure displayed only a modest shoulder formation near the strongest 3 × 3 beams.

Structural investigations of Pu{sup III} phosphate by X-ray diffraction, MAS-NMR and XANES spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Popa, Karin; Raison, Philippe E., E-mail: philippe.raison@ec.europa.eu; Martel, Laura

2015-10-15

PuPO{sub 4} was prepared by a solid state reaction method and its crystal structure at room temperature was solved by powder X-ray diffraction combined with Rietveld refinement. High resolution XANES measurements confirm the +III valence state of plutonium, in agreement with valence bond derivation. The presence of the americium (as β{sup −} decay product of plutonium) in the +III oxidation state was determined based on XANES spectroscopy. High resolution solid state {sup 31}P NMR agrees with the XANES results and the presence of a solid-solution. - Graphical abstract: A full structural analysis of PuPO{sub 4} based on Rietveld analysis ofmore » room temperature X-ray diffraction data, XANES and MAS NMR measurements was performed. - Highlights: • The crystal structure of PuPO{sub 4} monazite is solved. • In PuPO{sub 4} plutonium is strictly trivalent. • The presence of a minute amount of Am{sup III} is highlighted. • We propose PuPO{sub 4} as a potential reference material for spectroscopic and microscopic studies.« less

Mesoporous silica obtained with methyltriethoxysilane as co-precursor in alkaline medium

NASA Astrophysics Data System (ADS)

Putz, Ana-Maria; Wang, Kunzhou; Len, Adél; Plocek, Jiri; Bezdicka, Petr; Kopitsa, Gennady P.; Khamova, Tamara V.; Ianăşi, Cătălin; Săcărescu, Liviu; Mitróová, Zuzana; Savii, Cecilia; Yan, Minhao; Almásy, László

2017-12-01

Mesoporous silica particles have been synthesized by sol-gel method from tetraethoxysilane (tetraethylorthosilicate, TEOS) and methyltriethoxysilane (MTES), in ethanol and water mixture, at different ratios of the of the silica precursors. Ammonia was used as catalyst at room temperature and hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide, CTAB) as the structure directing agent. Nitrogen sorption, X-ray diffraction and small-angle neutron scattering gave information on the evolution of the gel structure and pore morphologies in the function of MTES/TEOS molar ratio. Thermogravimetric and differential thermal analysis showed that with addition of MTES the exothermic peak indicating the oxidation of the low molecular weight organic fragments shift to higher temperature. A room-temperature, one-pot synthesis of MCM-41 type materials is presented, in which the variation of the MTES concentration allows to change the hydrophobicity, preserving the specific properties materials, like the ordered pore structure, large specific surface area and high porosity. Specifically, the obtained materials had cylindrical pores, specific surface areas up to 1101 m2/g and total pore volumes up to 0.473 cm3/g. The obtained mesoporous materials are susceptible for further functionalization to improve their selective uptake of guest species in drug delivery applications.

Initial stages of ion beam-induced phase transformations in Gd2O3 and Lu2O3

NASA Astrophysics Data System (ADS)

Chen, Chien-Hung; Tracy, Cameron L.; Wang, Chenxu; Lang, Maik; Ewing, Rodney C.

2018-02-01

The atomic-scale evolution of lanthanide sesquioxides Gd2O3 and Lu2O3 irradiated with 1 MeV Kr ions at room temperature and 120 K, up to fluences of 1 × 1016 ions/cm2 (˜20 dpa), has been characterized by in situ transmission electron microscopy. At room temperature, both oxides exhibited high radiation tolerance. Irradiation did not cause any observable structural change in either material, likely due to the mobility of irradiation-induced point defects, causing efficient defect annihilation. For Gd2O3, having the larger cation ionic radius of the two materials, an irradiation-induced stacking fault structure appeared at low fluences in the low temperature irradiation. As compared with the cubic-to-monoclinic phase transformations known to result from higher energy (˜GeV) ion irradiation, Kr ions of lower energies (˜MeV) yield much lower rates of damage accumulation and thus less extensive structural modification. At a fluence of 2.5 × 1015 ions/cm2, only the initial stages of the cubic-to-monoclinic (C to B) phase transformation process, consisting of the formation and aggregation of defects, have been observed.

Development of Design Analysis Methods for C/SiC Composite Structures

NASA Technical Reports Server (NTRS)

Sullivan, Roy M.; Mital, Subodh K.; Murthy, Pappu L. N.; Palko, Joseph L.; Cueno, Jacques C.; Koenig, John R.

2006-01-01

The stress-strain behavior at room temperature and at 1100 C (2000 F) was measured for two carbon-fiber-reinforced silicon carbide (C/SiC) composite materials: a two-dimensional plain-weave quasi-isotropic laminate and a three-dimensional angle-interlock woven composite. Micromechanics-based material models were developed for predicting the response properties of these two materials. The micromechanics based material models were calibrated by correlating the predicted material property values with the measured values. Four-point beam bending sub-element specimens were fabricated with these two fiber architectures and four-point bending tests were performed at room temperature and at 1100 C. Displacements and strains were measured at various locations along the beam and recorded as a function of load magnitude. The calibrated material models were used in concert with a nonlinear finite element solution to simulate the structural response of these two materials in the four-point beam bending tests. The structural response predicted by the nonlinear analysis method compares favorably with the measured response for both materials and for both test temperatures. Results show that the material models scale up fairly well from coupon to subcomponent level.

Chiral discrimination in cyclodextrin complexes of amino acid derivatives: beta-cyclodextrin/N-acetyl-L-phenylalanine and N-acetyl-D-phenylalanine complexes.

PubMed

Alexander, Jennifer M; Clark, Joanna L; Brett, Tom J; Stezowski, John J

2002-04-16

In a systematic study of molecular recognition of amino acid derivatives in solid-state beta-cyclodextrin (beta-CD) complexes, we have determined crystal structures for complexes of beta-cyclodextrin/N-acetyl-L-phenylalanine at 298 and 20 K and for N-acetyl-D-phenylalanine at 298 K. The crystal structures for the N-acetyl-L-phenylalanine complex present disordered inclusion complexes for which the distribution of guest molecules at room temperature is not resolvable; however, they can be located with considerable confidence at low temperature. In contrast, the complex with N-acetyl-D-phenylalanine is well ordered at room temperature. The latter complex presents an example of a complex in this series in which a water molecule is included deeply in the hydrophobic torus of the extended dimer host. In an effort to understand the mechanisms of molecular recognition giving rise to the dramatic differences in crystallographic order in these crystal structures, we have examined the intermolecular interactions in detail and have examined insertion of the enantiomer of the D-complex into the chiral beta-CD complex crystal lattice.

Comparative Study of Two Different TiO2 Film Sensors on Response to H2 under UV Light and Room Temperature

PubMed Central

Peng, Xiaoying; Wang, Zhongming; Huang, Pan; Chen, Xun; Fu, Xianzhi; Dai, Wenxin

2016-01-01

An anatase TiO2 film sensor was prepared by a facile in-situ method on the interdigitated Au electrode deposited on the alumina substrate. The structure, morphology and the optical properties of the in-situ TiO2 film sensor were characterized by X-ray diffraction, Scanning Electron Microscopy, and UV-vis diffuse reflectance spectra. The photo-assisted gas sensitivities of the prepared film towards H2 gas were evaluated at room temperature in N2 and synthetic air atmospheres. As compared to TiO2 film sensor prepared by drop-coating method, this in-situ TiO2 film sensor exhibited a more compact structure composed of uniform TiO2 microspheres as well as a better gas sensitivity towards H2 under UV irradiation, especially in synthetic air. The photo-electrochemical measurements suggest that these improvements may be associated with the efficient charge transfer in the TiO2 interface induced by the TiO2 microsphere structure. This study might offer a feasible approach to develop photo-assisted gas sensors at ambient temperature. PMID:27509502

Effect of Growth Rate on Elevated Temperature Plastic Flow and Room Temperature Fracture Toughness of Directionally Solidified NiAl-31Cr-3Mo

NASA Technical Reports Server (NTRS)

Whittenberger, J. Daniel; Raj, S. V.; Locci, I. E.; Salem, J. A.

1999-01-01

The eutectic system Ni-33Al-31Cr-3Mo was directionally solidified at rates ranging from 7.6 to 508 mm/h. Samples were examined for microstructure and alloy chemistry, compression tested at 1200 and 1300 K, and subjected to room temperature fracture toughness measurements. Lamellar eutectic grains were formed at 12.7 mm/h; however cellular structures with a radial eutectic pattern developed at faster growth rates. Elevated temperature compression testing between 10(exp -4) to 10(exp -7)/s did not reveal an optimum growth condition, nor did any single growth condition result in a significant fracture toughness advantage. The mechanical behavior, taken together, suggests that Ni-33Al-31Cr-3Mo grown at rates from 25.4 to 254 mm/h will have nominally equivalent properties.

High temperature dielectric studies of indium-substituted NiCuZn nanoferrites

NASA Astrophysics Data System (ADS)

Hashim, Mohd.; Raghasudha, M.; Shah, Jyoti; Shirsath, Sagar E.; Ravinder, D.; Kumar, Shalendra; Meena, Sher Singh; Bhatt, Pramod; Alimuddin; Kumar, Ravi; Kotnala, R. K.

2018-01-01

In this study, indium (In3+)-substituted NiCuZn nanostructured ceramic ferrites with a chemical composition of Ni0.5Cu0.25Zn0.25Fe2-xInxO4 (0.0 ≤ x ≤ 0.5) were prepared by chemical synthesis involving sol-gel chemistry. Single phased cubic spinel structure materials were prepared successfully according to X-ray diffraction and transmission electron microscopy analyses. The dielectric properties of the prepared ferrites were measured using an LCR HiTester at temperatures ranging from room temperature to 300 °C at different frequencies from 102 Hz to 5 × 106 Hz. The variations in the dielectric parameters ε‧ and (tanδ) with temperature demonstrated the frequency- and temperature-dependent characteristics due to electron hopping between the ions. The materials had low dielectric loss values in the high frequency range at all temperatures, which makes them suitable for high frequency microwave applications. A qualitative explanation is provided for the dependences of the dielectric constant and dielectric loss tangent on the frequency, temperature, and composition. Mӧssbauer spectroscopy was employed at room temperature to characterize the magnetic behavior.

Field evaluation of spatial repellency of metofluthrin-impregnated latticework plastic strips against Aedes aegypti (L.) and analysis of environmental factors affecting its efficacy in My Tho City, Tien Giang, Vietnam.

PubMed

Kawada, Hitoshi; Iwasaki, Tomonori; LE Loan, Luu; Tien, Tran Khanh; Mai, Nguyen Thi Nhu; Shono, Yoshinori; Katayama, Yasuyuki; Takagi, Masahiro

2006-12-01

Spatial repellency of metofluthrin-impregnated polyethylene latticework plastic strips against Aedes aegypti mosquitoes was evaluated. Analysis of environmental factors affecting the efficacy of these strips, such as room temperature, humidity, and house structure, was performed in a residential area in My Tho City, Tien Giang Province, Vietnam. Treatment with the strips at the rate of 1 strip per 2.6-5.52 m(2) (approximately 600 mg per 2.6-5.52 m(2)) reduced the collection of Ae. aegypti resting inside the houses for at least eight weeks. Multiple regression analysis indicated that both increase in the average room temperature and decrease in the area of openings in the rooms that were treated with the strips positively affected the spatial repellency of metofluthrin.

Structure evolution and thermoelectric properties of carbonized polydopamine thin films

DOE PAGES

Li, Haoqi; Aulin, Yaroslav V.; Frazer, Laszlo; ...

2017-02-13

Carbonization of nature-inspired polydopamine can yield thin films with high electrical conductivity. Understanding of the structure of carbonized PDA (cPDA) is therefore highly desired. In this study, neutron diffraction, Raman spectroscopy, and other techniques indicate that cPDA samples are mainly amorphous with some short-range ordering and graphite-like structure that emerges with increasing heat treatment temperature. The electrical conductivity and the Seebeck coefficient show different trends with heat treatment temperature, while the thermal conductivity remains insensitive. Finally, the largest room-temperature ZT of 2 × 10 –4 was obtained on samples heat-treated at 800 °C, which is higher than that of reducedmore » graphene oxide.« less

Wood crib fire free burning test in ISO room

NASA Astrophysics Data System (ADS)

Qiang, Xu; Griffin, Greg; Bradbury, Glenn; Dowling, Vince

2006-04-01

In the research of application potential of water mist fire suppression system for fire fighting in train luggage carriage, a series of experiments were conducted in ISO room on wood crib fire with and without water mist actuation. The results of free burn test without water mist suppression are used as reference in evaluating the efficiency of water mist suppression system. As part of the free burn test, several tests have been done under the hood of ISO room to calibrate the size of the crib fire and these tests can also be used in analyzing the wall effect in room fire hazard. In these free burning experiments, wood cribs of four sizes under the hood were tested. The temperature of crib fire, heat flux around the fire, gas concentration in hood of ISO room were measured in the experiments and two sets of thermal imaging system were used to get the temperature distribution and the typical shape of the free burning flames. From the experiments, the radiation intensity in specific positions around the fire, the effective heat of combustion, mass loss, oxygen consumption rate for different sizes of fire, typical structure of the flame and self extinguishment time was obtained for each crib size.

Cholinium-amino acid based ionic liquids: a new method of synthesis and physico-chemical characterization.

PubMed

De Santis, Serena; Masci, Giancarlo; Casciotta, Francesco; Caminiti, Ruggero; Scarpellini, Eleonora; Campetella, Marco; Gontrani, Lorenzo

2015-08-28

In the present work we report the synthesis and physico-chemical characterization in terms of the viscosity and density of a wide series of cholinium-amino acid based room temperature ionic liquids ([Ch][AA] RTILs). 18 different amino acids were used to obtain 14 room temperature ILs. Among the most common AAs, only valine did not form an RTIL but it is a liquid above 80 °C. With respect to the methods reported in the literature we propose a synthesis based on potentiometric titration which has several advantages such as shorter preparation time, stoichiometry within ±1%, very high yields (close to 100%), high reproducibility, and no use of organic solvents, thus being more environmentally friendly. We tried to prepare dianionic ILs with some AAs with two potentially ionisable groups but in all cases the salts were solids at room temperature. All the ILs were characterized by (1)H NMR to confirm the stoichiometry. Physico-chemical properties such as density, viscosity, refractive index and conductivity were measured as a function of temperature and correlated with empirical equations. The values were compared with the data already reported in the literature for some [Ch][AA] ILs. The thermal expansion coefficient αp and the molar volume Vm were also calculated from the experimental density values. Due to the high number of AAs explored and their structural heterogeneity we have been able to find some interesting correlations between the data obtained and the structural features of the AAs in terms of the alkyl chain length, hydrogen bonding ability, stacking and cyclization. Some parameters were also found to be in good agreement with those reported for other ILs. We think that these data can give an important contribution to the understanding of the structure-property relationship of ILs because they focused on the structural effect of the anions, while most data in the literature are focussed on the cations.

Growth of wurtzite CdTe nanowires on fluorine-doped tin oxide glass substrates and room-temperature bandgap parameter determination

NASA Astrophysics Data System (ADS)

Choi, Seon Bin; Song, Man Suk; Kim, Yong

2018-04-01

The growth of CdTe nanowires, catalyzed by Sn, was achieved on fluorine-doped tin oxide glass by physical vapor transport. CdTe nanowires grew along the 〈0001〉 direction, with a very rare and phase-pure wurtzite structure, at 290 °C. CdTe nanowires grew under Te-limited conditions by forming SnTe nanostructures in the catalysts and the wurtzite structure was energetically favored. By polarization-dependent and power-dependent micro-photoluminescence measurements of individual nanowires, heavy and light hole-related transitions could be differentiated, and the fundamental bandgap of wurtzite CdTe at room temperature was determined to be 1.562 eV, which was 52 meV higher than that of zinc-blende CdTe. From the analysis of doublet photoluminescence spectra, the valence band splitting energy between heavy hole and light hole bands was estimated to be 43 meV.

Nanoparticles of nickel oxide: growth and organization on zinc-substituted anionic clay matrix by one-pot route at room temperature

NASA Astrophysics Data System (ADS)

Carja, Gabriela; Nakajima, Akira; Dranca, Cristian; Okada, Kiyoshi

2010-10-01

A room temperature nanocarving strategy is developed for the fabrication of nanoparticles of nickel oxide on zinc-substituted anionic clay matrix (Ni/ZnLDH). It is based on the growth and organization of nanoparticles of nickel oxide which occur during the structural reconstruction of the layered structure of the anionic clay in NiSO4 aqueous solution. No organic compounds are used during the fabrication. The described material was characterized by X-ray diffraction (XRD), IR spectroscopy (FTIR), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Results show that the nickel-clay nanoarchitecture consists of small nanoparticles of nickel oxide (average size 7 nm) deposited on the larger nanoparticles (average size 90 nm) of zinc-substituted clay. The optical properties of the new nickel-zinc formulation are studied by UV-Vis.

Mechanism of room temperature oxygen sensor based on nanocrystalline TiO2 film

NASA Astrophysics Data System (ADS)

Bakri, A. S.; Sahdan, M. Z.; Nafarizal, N.; Abdullah, S. A.; Said, N. D. M.; Raship, N. A.; Sari, Y.

2018-04-01

A titanium dioxide (TiO2) thin film is proposed as the active layer for the detection of oxygen gas. The sensor is fabricated on silicon wafer using sol-gel dip coating technique with a constant withdrawal speed. The field emission scanning electron microscope image reveals that the film has a uniform structure while the x-ray diffraction analysis indicates that the film is anatase phase with tetragonal lattice structure. The film exhibit the highest intensity peak at (101) plane. The surface roughness measurement shows that the film has low surface roughness with small grain size. The electrical studies revealed that the resistivity is about 4.02 x 10-3 Ω.cm and the thickness of TiO2 film is 127.44 nm. The gas sensor measurement showed that the sensor response of the film is about 4.21% at room temperature.

TGA, Hirshfeld, Raman spectroscopy and computational studies of diethylammonium hexachloroplumbate [(C2H5)2NH2]2PbCl6

NASA Astrophysics Data System (ADS)

Ouasri, A.; El-Adel, L.; Zouihri, H.; Rhandour, A.; Jalbout, A. F.

2018-04-01

Diethylammonium hexachloroplumbate [(C2H5)2NH2]2PbCl6 was found to be monoclinic with P21/n (Z = 2) as space group at room temperature. The TGA analysis shows that this compound is slightly hygroscopic and presents moisture in itself. The Raman spectrum (50-4000 cm-1) of this compound recorded at room temperature was discussed on the basis of the factor group analysis using the structural data obtained recently [5]. The experimental frequencies are compared to those obtained by Density Functional Theory (DFT) by using the B3LYP functional and the 6-31G(d) (SDD) basis set. The thermodynamic properties and geometries of this compound have been determinated and characterized. The significant intermolecular interactions in the crystal structure are identified and analyzed using the Hirshfeld surface and fingerprint plots computational methods.

Structure of the Clean and Oxygen-Covered Cu(100) Surface at Room Temperature in the Presence of Methanol Vapor in the 10-200 mTorr Pressure Range.

PubMed

Eren, Baran; Kersell, Heath; Weatherup, Robert S; Heine, Christian; Crumlin, Ethan J; Friend, Cynthia M; Salmeron, Miquel B

2018-01-18

Using ambient pressure X-ray photoelectron spectroscopy (APXPS) and high pressure scanning tunneling microscopy (HPSTM), we show that in equilibrium with 0.01-0.2 Torr of methanol vapor, at room temperature, the Cu(100) surface is covered with methoxy species forming a c(2 × 2) overlayer structure. In contrast, no methoxy is formed if the surface is saturated with an ordered oxygen layer, even when the methanol pressure is 0.2 Torr. At oxygen coverages below saturation, methanol dissociates and reacts with the atomic oxygen, producing methoxy and formate on the surface, and formaldehyde that desorbs to the gas phase. Unlike the case of pure carbon monoxide and carbon dioxide, methanol does not induce the restructuring of the Cu(100) surface. These results provide insight into catalytic anhydrous production of aldehydes.

Invited article: Dielectric material characterization techniques and designs of high-Q resonators for applications from micro to millimeter-waves frequencies applicable at room and cryogenic temperatures.

PubMed

Le Floch, Jean-Michel; Fan, Y; Humbert, Georges; Shan, Qingxiao; Férachou, Denis; Bara-Maillet, Romain; Aubourg, Michel; Hartnett, John G; Madrangeas, Valerie; Cros, Dominique; Blondy, Jean-Marc; Krupka, Jerzy; Tobar, Michael E

2014-03-01

Dielectric resonators are key elements in many applications in micro to millimeter wave circuits, including ultra-narrow band filters and frequency-determining components for precision frequency synthesis. Distributed-layered and bulk low-loss crystalline and polycrystalline dielectric structures have become very important for building these devices. Proper design requires careful electromagnetic characterization of low-loss material properties. This includes exact simulation with precision numerical software and precise measurements of resonant modes. For example, we have developed the Whispering Gallery mode technique for microwave applications, which has now become the standard for characterizing low-loss structures. This paper will give some of the most common characterization techniques used in the micro to millimeter wave regime at room and cryogenic temperatures for designing high-Q dielectric loaded cavities.

All-Electrical Spin Field Effect Transistor in van der Waals Heterostructures at Room Temperature

NASA Astrophysics Data System (ADS)

Dankert, André; Dash, Saroj

Spintronics aims to exploit the spin degree of freedom in solid state devices for data storage and information processing. Its fundamental concepts (creation, manipulation and detection of spin polarization) have been demonstrated in semiconductors and spin transistor structures using electrical and optical methods. However, an unsolved challenge is the realization of all-electrical methods to control the spin polarization in a transistor manner at ambient temperatures. Here we combine graphene and molybdenum disulfide (MoS2) in a van der Waals heterostructure to realize a spin field-effect transistor (spin-FET) at room temperature. These two-dimensional crystals offer a unique platform due to their contrasting properties, such as weak spin-orbit coupling (SOC) in graphene and strong SOC in MoS2. The gate-tuning of the Schottky barrier at the MoS2/graphene interface and MoS2 channel yields spins to interact with high SOC material and allows us to control the spin polarization and lifetime. This all-electrical spin-FET at room temperature is a substantial step in the field of spintronics and opens a new platform for testing a plethora of exotic physical phenomena, which can be key building blocks in future device architectures.

Enhancement of Impact Toughness by Delamination Fracture in a Low-Alloy High-Strength Steel with Al Alloying

NASA Astrophysics Data System (ADS)

Sun, Junjie; Jiang, Tao; Liu, Hongji; Guo, Shengwu; Liu, Yongning

2016-12-01

The effect of delamination toughening of martensitic steel was investigated both at room and low temperatures [253 K and 233 K (-20 °C and -40 °C)]. Two low-alloy martensitic steels with and without Al alloying were both prepared. Layered structure with white band and black matrix was observed in Al alloyed steel, while a homogeneous microstructure was displayed in the steel without Al. Both steels achieved high strength (tensile strength over 1600 MPa) and good ductility (elongation over 11 pct), but they displayed stark contrasts on impact fracture mode and Charpy impact energy. Delamination fracture occurred in Al alloyed steel and the impact energies were significantly increased both at room temperature (from 75 to 138 J, i.e., nearly improved up to 2 times) and low temperatures [from 47.9 to 71.3 J at 233 K (-40 °C)] compared with the one without Al. Alloying with Al promotes the segregation of Cr, Mn, Si and C elements to form a network structure, which is martensite with higher carbon content and higher hardness than that of the matrix. And this network structure evolved into a band structure during the hot rolling process. The difference of yield stress between the band structure and the matrix gives rise to a delamination fracture during the impact test, which increases the toughness greatly.

Critical role of the coupling between the octahedral rotation and A -site ionic displacements in PbZr O3 -based antiferroelectric materials investigated by in situ neutron diffraction

NASA Astrophysics Data System (ADS)

Lu, Teng; Studer, Andrew J.; Yu, Dehong; Withers, Ray L.; Feng, Yujun; Chen, Hua; Islam, S. S.; Xu, Zhuo; Liu, Yun

2017-12-01

This in situ neutron-diffraction study on antiferroelectric (AFE) P b0.99(N b0.02Z r0.65S n0.28T i0.05 ) O3 polycrystalline materials describes systematic structural and associated preferred orientation changes as a function of applied electric field and temperature. It is found that the pristine AFE phase can be poled into the metastable ferroelectric (FE) phase at room temperature. At this stage, both AFE and FE phases consist of modes associated with octahedral rotation and A -site ionic displacements. The temperature-induced phase transition indicates that the octahedral rotation and ionic displacements are weakly coupled in the room-temperature FE phase and decoupled in the high-temperature FE phase. However, both temperature and E -field-induced phase transitions between the AFE and high-temperature FE phase demonstrate the critical role of coupling between octahedral rotation and A -site ionic displacements in stabilizing the AFE structure, which provides not only experimental evidence to support previous theoretical calculations, but also an insight into the design and development of AFE materials. Moreover, the associated preferred orientation evolution in both AFE and FE phases is studied during the phase transitions. It is found that the formation of the preferred orientation can be controlled to tune the samples' FE and AFE properties.

Dielectric studies of Co3-xMnxO4 (x=0.1-1.0) cubic spinel multiferroic

NASA Astrophysics Data System (ADS)

Meena, P. L.; Kumar, Ravi; Prajapat, C. L.; Sreenivas, K.; Gupta, Vinay

2009-07-01

A series of Co3-xMnxO4 (x =0.1-1.0) multiferroic cubic spinel ceramics were prepared to study the effect of Mn substitution at Co site on the crystal structures and dielectric properties. No significant change in the structural symmetry was observed with increasing x up to 1.0. A linear increase in lattice parameter with x is attributed to the substitution of Co3+ by Mn3+ (large ionic radii) at the octahedral sites. An antiferromagnetic-type ordering of Co3O4 changes to ferrimagnetic-type order after incorporation of Mn. The effect of Mn substitution on the dielectric constant and loss tangent was studied over a wide range of frequency (75 kHz-5 MHz) and temperature of 150-450 K. The measured value of room temperature ac conductivity at 1.0 MHz was found to increase from 2.0×10-6 to 4.4×10-4 Ω-1 cm-1 and follows power law (σac=Aωs) behavior. The dielectric constant ɛ'(ω) shows a weak frequency dispersion and small temperature dependence below 250 K for all ceramic samples. However, a strong temperature and frequency dependence on ɛ'(ω) was observed at higher temperature (>250 K). The temperature dependent ɛ'(ω) data show the existence of room temperature ferroelectricity in all prepared samples.

Photophysical properties of ortho-metalated monomeric and dimeric complexes containing rhodium(III) and iridium(III) metal centers

NASA Astrophysics Data System (ADS)

Marshall, Jason Alexander

Photophysical properties of dichloro-bridged dimers and monomeric tris complexes of the type [M(NC)2Cl]2 and M(NC)3, where NC refers to the ortho-metalating ligands 2-phenylpyridine (ppy), benzo[h]quinoline (bzq), or 2-(p-tolyl)pyridine (ptpy) and M is Rh(III) or Ir(III), were investigated. Excited-state emission of Rh(III) complexes are highly structured and independent of temperature from 4--100 K in glassy media, with long lifetimes (102 mus to ms). Emission is not observed from the pale yellow, fluid solutions of Rh(III) complexes at room temperature. Below 7K, decay kinetics are sensitive to temperature and are complicated, requiring multi-exponential fits in 4:1 EtOH/MeOH. The spectroscopic properties are consistent with the assignment of a lowest 3pipi* excited-state manifold perturbed by an admixture of higher-lying states possessing strong spin-orbit interactions. The complicated decays are attributed to spin-relaxation-limited behavior between spin-levels in the 3pipi* manifold. Deep yellow solutions of Ir(III) complexes in 4:1 EtOH/MeOH are observed to emit in both glassy media and in fluid solution, displaying severe changes in spectral shape as the glass softens which are not attributable to rigidochromic shifts. Low-temperature spectra are structured with emission origins in the range 496--520 nm whereas room-temperature emission of complexes in fluid solution are characteristically broad structureless bands with maxima redshifted from spectra measured in rigid media. Both the emission and the excited-state lifetimes display temperature dependence, with lifetimes in the microsecond to tens of microseconds range at 77 K, increasing by more than an order of magnitude as the temperature is decreased to 4 K. Each of these characteristic band shapes arises from separate components of the emission which have been time-resolved from the low-temperature spectrum. A long-lived, structured component of the emission, only observed in rigid media, has been assigned as 3pipi*. The spectroscopic properties of the short-lived component, observed in the time-resolved low-temperature emission spectrum and in the room-temperature fluid-solution emission spectrum, are consistent with a lowest 3MLCT excited state manifold.

Stainless steel component with compressed fiber Bragg grating for high temperature sensing applications

NASA Astrophysics Data System (ADS)

Jinesh, Mathew; MacPherson, William N.; Hand, Duncan P.; Maier, Robert R. J.

2016-05-01

A smart metal component having the potential for high temperature strain sensing capability is reported. The stainless steel (SS316) structure is made by selective laser melting (SLM). A fiber Bragg grating (FBG) is embedded in to a 3D printed U-groove by high temperature brazing using a silver based alloy, achieving an axial FBG compression of 13 millistrain at room temperature. Initial results shows that the test component can be used for up to 700°C for sensing applications.

Room temperature single-photon detectors for high bit rate quantum key distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comandar, L. C.; Patel, K. A.; Engineering Department, Cambridge University, 9 J J Thomson Ave., Cambridge CB3 0FA

We report room temperature operation of telecom wavelength single-photon detectors for high bit rate quantum key distribution (QKD). Room temperature operation is achieved using InGaAs avalanche photodiodes integrated with electronics based on the self-differencing technique that increases avalanche discrimination sensitivity. Despite using room temperature detectors, we demonstrate QKD with record secure bit rates over a range of fiber lengths (e.g., 1.26 Mbit/s over 50 km). Furthermore, our results indicate that operating the detectors at room temperature increases the secure bit rate for short distances.

Seasonal mapping of NICU temperature.

PubMed

Thomas, Karen A; Magbalot, Almita; Shinabarger, Kelley; Mokhnach, Larisa; Anderson, Marilyn; Diercks, Kristi; Millar, April; Thorngate, Lauren; Walker, Wendy; Dilback, Nancy; Berkan, Maureen

2010-04-01

To create a thermal map of ambient air, radiant, and evaporative temperatures and humidity throughout the NICU nursery by season across a calendar year. Each cubicle of the 32-bed NICU, distributed across 5 rooms, in a level III nursery was measured. Temperatures were recorded at a consistent time on one day during January, April, July, and October. An electronic monitor (QUESTemp degrees 34; Quest Technologies, Oconomowoc, Wisconsin) was used to measure dry bulb, wet bulb, and globe thermometer temperatures. Analysis of variance revealed statistically significant (P < .000) differences in season, room, and season by room interaction. Room ambient air temperatures differed by less than 2 degrees F across season. Radiant temperature paralleled air temperature. Humidity, the predominant difference across season, produced evaporative temperatures considerably lower than room air temperature, and the gradient between mean nursery dry bulb temperature and wet bulb temperature was 9.3 degrees F in summer and 16.8 degrees F in winter. The thermal map revealed seasonal thermal differences, particularly in humidity level and evaporative temperature. Room temperature alone does not reflect the total thermal environment. Recommendations include periodic assessment of nurseries along with air, evaporative, and radiant temperatures as well as humidity to fully appreciate the impact of the thermal environment on infants.

Seasonal mapping of NICU temperature.

PubMed

Thomas, Karen A; Magbalot, Almita; Shinabarger, Kelley; Mokhnach, Larisa; Anderson, Marilyn; Diercks, Kristi; Millar, April; Thorngate, Lauren; Walker, Wendy; Dilback, Nancy; Berkan, Maureen

2010-10-01

To create a thermal map of ambient air, radiant, and evaporative temperatures and humidity throughout the NICU nursery by season across a calendar year. Each cubicle of the 32-bed NICU, distributed across 5 rooms, in a level III nursery was measured. Temperatures were recorded at a consistent time on one day during January, April, July, and October. : An electronic monitor (QUESTemp ° 34; Quest Technologies, Oconomowoc, Wisconsin) was used to measure dry bulb, wet bulb, and globe thermometer temperatures. Analysis of variance revealed statistically significant (P ≤ .000) differences in season, room, and season by room interaction. Room ambient air temperatures differed by less than 2 ° F across season. Radiant temperature paralleled air temperature. Humidity, the predominant difference across season, produced evaporative temperatures considerably lower than room air temperature, and the gradient between mean nursery dry bulb temperature and wet bulb temperature was 9.3 ° F in summer and 16.8 ° F in winter. The thermal map revealed seasonal thermal differences, particularly in humidity level and evaporative temperature. Room temperature alone does not reflect the total thermal environment. Recommendations include periodic assessment of nurseries along with air, evaporative, and radiant temperatures as well as humidity to fully appreciate the impact of the thermal environment on infants.

Research on automatic control system of greenhouse

NASA Astrophysics Data System (ADS)

Liu, Yi; Qi, Guoyang; Li, Zeyu; Wu, Qiannan; Meng, Yupeng

2017-03-01

This paper introduces a kind of automatic control system of single-chip microcomputer and a temperature and humidity sensor based on the greenhouse, describes the system's hardware structure, working principle and process, and a large number of experiments on the effect of the control system, the results show that the system can ideally control temperature and room temperature and humidity, can be used in indoor breeding and planting, and has the versatility and portability.

Structural and magnetic phase transitions in gadolinium under high pressures and low temperatures

DOE PAGES

Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; ...

2014-11-07

High pressure structural transition studies have been carried out on rare earth metal gadolinium in a diamond anvil cell at room temperature to 169 GPa. Gadolinium has been compressed to 38% of its initial volume at this pressure. With increasing pressure, a crystal structure sequence of hcp → Smtype→ dhcp → fcc → dfcc → monoclinic has been observed in our studies on gadolinium. The measured equation of state of gadolinium is presented to 169 GPa at ambient temperature. Magnetic ordering temperature of gadolinium has been studied using designer diamond anvils to a pressure of 25 GP and a temperaturemore » of 10 K. The magnetic ordering temperature has been determined from the four-point electrical resistivity measurements carried out on gadolinium. Furthermore, our experiments show that the magnetic transition temperature decreases with increasing pressure to 19 GPa and then increases when gadolinium is subjected to higher pressures.« less

Structural and magnetic phase transitions in gadolinium under high pressures and low temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.

High pressure structural transition studies have been carried out on rare earth metal gadolinium in a diamond anvil cell at room temperature to 169 GPa. Gadolinium has been compressed to 38% of its initial volume at this pressure. With increasing pressure, a crystal structure sequence of hcp → Smtype→ dhcp → fcc → dfcc → monoclinic has been observed in our studies on gadolinium. The measured equation of state of gadolinium is presented to 169 GPa at ambient temperature. Magnetic ordering temperature of gadolinium has been studied using designer diamond anvils to a pressure of 25 GP and a temperaturemore » of 10 K. The magnetic ordering temperature has been determined from the four-point electrical resistivity measurements carried out on gadolinium. Furthermore, our experiments show that the magnetic transition temperature decreases with increasing pressure to 19 GPa and then increases when gadolinium is subjected to higher pressures.« less

Structural, dielectric and magnetic studies of magnetoelectric trirutile Fe{sub 2}TeO{sub 6}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaushik, S. D., E-mail: sdkaushik@csr.res.in; Sahu, B.; Mohapatra, S. R.

2016-05-23

We have investigated structural, magnetic and dielectric properties of Fe{sub 2}TeO{sub 6} which is a magnetoelectric antiferromagnet with the trirutile lattice. Rietveld analysis of room temperature X-ray diffraction data shows the phase purity of the sample with tetragonal trirutile structure (space group P4{sub 2}/mnm). The DC susceptibility measurement performed on polycrystalline powders exhibits antiferromagnetic ordering below transition temperature ~ 210K. The employment of Curie-Weiss law to inverse magnetic susceptibility only in the temperature range 350-260 K indicates the magnetic ordering starts developing before the transition temperature. The temperature dependent dielectric measurements show an intrinsic behavior of dielectric constant below 150more » K while a continuous increase in dielectric constant with temperature above 150 K may be attributed to a small increase in electrical conduction, known commonly in the literatures.« less

Structural, electrical, and optical properties of antimony-doped tin oxide films prepared at room temperature by radio frequency magnetron sputtering for transparent electrodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Sung Uk; Hong, Byungyou; Choi, Won Seok

2009-07-15

Antimony-doped tin oxide (ATO) films were prepared on 7059 Corning glass substrate by the radio frequency (rf) magnetron sputtering method using SnO{sub 2} target mixed with Sb of 6 wt % at room temperature. The working pressure was varied from 0.67 to 2 Pa in steps of 0.67 Pa, and the rf power was varied from 100 to 175 W in steps of 25 W at room temperature. The thickness of the deposited ATO films was about 150 nm. X-ray diffraction (XRD) measurements showed the ATO films to be crystallized with a strong (101) preferred orientation as the rf powermore » is increased. The spectra revealed that the deposited films were polycrystalline, retaining the tetragonal structure. The grain size was estimated from the XRD spectra using the Scherrer equation and found to decrease with a decrease in the working pressure and an increase in the rf power, while the surface roughness was observed to be smoothened. The ATO film that was deposited at a working pressure of 0.67 Pa with rf power of 175 W showed the lowest resistivity of 8.6x10{sup -3} {Omega} cm, and the optical transmittance was 86.5% in the visible wavelength range from 400 to 800 nm.« less

Enhanced room temperature ferromagnetism in Cr-doped ZnO nanoparticles prepared by auto-combustion method

NASA Astrophysics Data System (ADS)

Haq, Khizar-ul; Irfan, M.; Masood, Muhammad; Saleem, Murtaza; Iqbal, Tahir; Ahmad, Ishaq; Khan, M. A.; Zaffar, M.; Irfan, Muhammad

2018-04-01

Zn1‑x Cr x O (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.09) nanoparticles were synthesized, by an auto-combustion method. Structural, optical, and magnetic characteristics of Cr-doped ZnO samples calcined at 600 °C have been analyzed by using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), UV–Vis spectroscopy and vibrating sample magnetometer (VSM). The XRD data confirmed the hexagonal wurtzite structure of pure and Cr-doped ZnO nanoparticles. The calculated values of grain size using Scherrer's formula are in the range of 30.7–9.2 nm. The morphology of nanopowders has been observed by FESEM, and EDS results confirmed a systematic increase of Cr content in the samples and clearly indicate with no impurity element. The band gaps, computed by UV–Vis spectroscopy, are in the range of 2.83–2.35 eV for different doping concentrations. By analyzing VSM data, significantly enhanced room temperature ferromagnetism is identified in Cr-doped ZnO samples. The value of magnetization is a 12 times increased of the value reported by Daunet al. (2010). Room temperature ferromagnetism of the nanoparticles is of vital prominence for spintronics applications. Project supported by the Office of Research, Innovation, and Commercialization (ORIC), MUST Mirpur (AJK).

CuInP 2S 6 Room Temperature Layered Ferroelectric

DOE PAGES

Belianinov, Alex; He, Qian; Dziaugys, Andrius; ...

2015-05-01

In this paper, we explore ferroelectric properties of cleaved 2-D flakes of copper indium thiophosphate, CuInP 2S 6 (CITP), and probe size effects along with limits of ferroelectric phase stability, by ambient and ultra high vacuum scanning probe microscopy. CITP belongs to the only material family known to display ferroelectric polarization in a van der Waals, layered crystal at room temperature and above. Our measurements directly reveal stable, ferroelectric polarization as evidenced by domain structures, switchable polarization, and hysteresis loops. We found that at room temperature the domain structure of flakes thicker than 100 nm is similar to the cleavedmore » bulk surfaces, whereas below 50 nm polarization disappears. We ascribe this behavior to a well-known instability of polarization due to depolarization field. Furthermore, polarization switching at high bias is also associated with ionic mobility, as evidenced both by macroscopic measurements and by formation of surface damage under the tip at a bias of 4 V—likely due to copper reduction. Mobile Cu ions may therefore also contribute to internal screening mechanisms. Finally, the existence of stable polarization in a van-der-Waals crystal naturally points toward new strategies for ultimate scaling of polar materials, quasi-2D, and single-layer materials with advanced and nonlinear dielectric properties that are presently not found in any members of the growing “graphene family”.« less

Single molecule dynamics at a mechanically controllable break junction in solution at room temperature.

PubMed

Konishi, Tatsuya; Kiguchi, Manabu; Takase, Mai; Nagasawa, Fumika; Nabika, Hideki; Ikeda, Katsuyoshi; Uosaki, Kohei; Ueno, Kosei; Misawa, Hiroaki; Murakoshi, Kei

2013-01-23

The in situ observation of geometrical and electronic structural dynamics of a single molecule junction is critically important in order to further progress in molecular electronics. Observations of single molecular junctions are difficult, however, because of sensitivity limits. Here, we report surface-enhanced Raman scattering (SERS) of a single 4,4'-bipyridine molecule under conditions of in situ current flow in a nanogap, by using nano-fabricated, mechanically controllable break junction (MCBJ) electrodes. When adsorbed at room temperature on metal nanoelectrodes in solution to form a single molecule junction, statistical analysis showed that nontotally symmetric b(1) and b(2) modes of 4,4'-bipyridine were strongly enhanced relative to observations of the same modes in solid or aqueous solutions. Significant changes in SERS intensity, energy (wavenumber), and selectivity of Raman vibrational bands that are coincident with current fluctuations provide information on distinct states of electronic and geometrical structure of the single molecule junction, even under large thermal fluctuations occurring at room temperature. We observed the dynamics of 4,4'-bipyridine motion between vertical and tilting configurations in the Au nanogap via b(1) and b(2) mode switching. A slight increase in the tilting angle of the molecule was also observed by noting the increase in the energies of Raman modes and the decrease in conductance of the molecular junction.

Microstructure and Room-Temperature Mechanical Properties of FeCrMoVTi x High-Entropy Alloys

NASA Astrophysics Data System (ADS)

Guo, Jun; Huang, Xuefei; Huang, Weigang

2017-07-01

FeCrMoVTi x ( x values represent the molar ratio, where x = 0, 0.5, 1.0, 1.5, and 2.0) high-entropy alloys were prepared by a vacuum arc melting method. The effects of Ti element on the microstructure and room-temperature mechanical properties of the as-cast FeCrMoVTi x alloys were investigated. The results show that the prepared alloys exhibited typical dendritic microstructure and the size of the microstructure became fine with increasing Ti content. The FeCrMoV alloy exhibited a single body-centered cubic structure (BCC1) and the alloys prepared with Ti element exhibited BCC1 + BCC2 mixed structure. The new BCC2 phase is considered as (Fe, Ti)-rich phase and was distributed in the dendrite region. With the increase of Ti content, the volume fraction of the BCC2 phase increased and its shape changed from a long strip to a network. For the FeCrMoV alloy, the fracture strength, plastic strain, and hardness reached as high as 2231 MPa, 28.2%, and 720 HV, respectively. The maximum hardness of 887 HV was obtained in the FeCrMoVTi alloy. However, the fracture strength, yield stress, and plastic strain of the alloys decreased continuously as Ti content increased. In the room-temperature compressive test, the alloys showed typical brittle fracture characteristics.

Epitaxial Growth and Electronic Structure of Half Heuslers Co1-xNixTiSb (001), Ni1-xCoxTiSn, and PtLuSb

DTIC Science & Technology

2016-01-09

studied in detail using scanning tunneling microscopy and angle resolved photoemission. For the doping levels achieved in cobalt titanium antimony, the...angle resolved photoemission. For the doping levels achieved in cobalt titanium antimony, the electron mobility at room temperature was comparable...scanning tunneling microscopy and angle resolved photoemission. For the doping levels achieved in cobalt titanium antimony, the electron mobility at room

Diamond structure recovery during ion irradiation at elevated temperatures

NASA Astrophysics Data System (ADS)

Deslandes, Alec; Guenette, Mathew C.; Belay, Kidane; Elliman, Robert G.; Karatchevtseva, Inna; Thomsen, Lars; Riley, Daniel P.; Lumpkin, Gregory R.

2015-12-01

CVD diamond is irradiated by 5 MeV carbon ions, with each sample held at a different temperature (300-873 K) during irradiations. The defect structures resulting from the irradiations are evident as vacancy, interstitial and amorphous carbon signals in Raman spectra. The observed variation of the full width at half maximum (FWHM) and peak position of the diamond peak suggests that disorder in the diamond lattice is reduced for high temperature irradiations. The dumbbell interstitial signal is reduced for irradiations at 873 K, which suggests this defect is unstable at these temperatures and that interstitials have migrated to crystal surfaces. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy results indicate that damage to the diamond structure at the surface has occurred for room temperature irradiations, however, this structure is at least partially recovered for irradiations performed at 473 K and above. The results suggest that, in a high temperature irradiation environment such as a nuclear fusion device, in situ annealing of radiation-created defects can maintain the diamond structure and prolong the lifetime of diamond components.

How mothers keep their babies warm.

PubMed Central

Bacon, C J; Bell, S A; Clulow, E E; Beattie, A B

1991-01-01

Details of room temperature, clothing, and bedding used by night and by day and in winter and in summer were recorded for 649 babies aged 8 to 26 weeks. Room temperature at night was significantly related to outside temperature and duration of heating. Total insulation was significantly related to outside temperature and to minimum room temperature, but there was wide variation in insulation at the same room temperature. High levels of insulation for a given room temperature were found particularly at night and in winter, and were associated with the use of thick or doubled duvets and with swaddling. At least half the babies threw off some or all of their bedding at night, and at least a quarter sweated. Younger mothers and mothers in the lower social groups put more bedclothes over their babies, and the latter also kept their rooms warmer. Many mothers kept their babies warmer during infections. PMID:2039255

Microplastic Deformation of Submicrocrystalline Copper at Room and Elevated Temperatures

NASA Astrophysics Data System (ADS)

Dudarev, E. F.; Pochivalova, G. P.; Tabachenko, A. N.; Maletkina, T. Yu.; Skosyrskii, A. B.; Osipov, D. A.

2017-02-01

of investigations of submicrocrystalline copper subjected to cold rolling after abc pressing by methods of backscatter electron diffraction and x-ray diffraction analysis are presented. It is demonstrated that after such combined intensive plastic deformation, the submicrocrystalline structure with average grain-subgrain structure elements having sizes of 0.63 μm is formed with relative fraction of high-angle grain boundaries of 70% with texture typical for rolled copper. Results of investigation of microplastic deformation of copper with such structure at temperatures in the interval 295-473 K and with submicrocrystalline structure formed by cold rolling of coarse-grained copper are presented.

Synthesis, Resistivity, and Thermal Properties of the Cubic Perovskite NH 2CH=NH 2SnI 3and Related Systems

NASA Astrophysics Data System (ADS)

Mitzi, D. B.; Liang, K.

1997-12-01

Combining concentrated hydriodic acid solutions of tin(II) iodide and formamidine acetate in an inert atmosphere results in the precipitation of a new conducting organic-inorganic compound, NH 2CH=NH 2SnI 3, which at room temperature adopts a cubic perovskite structure. The lattice constant for NH 2CH=NH 2SnI 3is found to be a=6.316(1) Å, which is approximately 1.2% larger than that for the isostructural compound CH 3NH 3SnI 3. The electrical resistivity of a pressed pellet of the new compound exhibits semimetallic temperature dependence from 10 to 300 K, with evidence of a structural transition at approximately 75 K. NH 2CH=NH 2SnI 3begins to slowly decompose in an inert atmosphere at temperatures as low as 200°C, with bulk decomposition/melting occurring above 300°C. The properties of the formamidinium-based perovskite are compared with those of the related cubic (at room temperature) perovskite CH 3NH 3SnI 3and the mixed-cation system (CH 3NH 3) 1- x(NH 2CH=NH 2) xSnI 3.

Magnetic and magnetocaloric properties of Co2-xFexVGa Heusler alloys

NASA Astrophysics Data System (ADS)

Schroeder, K.; Waybright, J.; Kharel, P.; Zhang, W.; Valloppilly, S.; Herran, J.; Lukashev, P.; Huh, Y.; Skomski, R.; Sellmyer, D. J.

2018-05-01

The magnetic and magnetocaloric properties of iron-substituted Co2VGa alloys, Co2-xFexVGa (x = 0, 0.1, 0.15, 0.2, 0.3), were investigated. The Fe-substituted samples, prepared by arc melting, melt spinning, and annealing, crystallized in the L21 Heusler structure, without any secondary phases. The Curie temperature and high-field magnetization at 50 K decreased from 345 K and 44 emu/g (1.90 μB/f.u.) for Co2VGa to 275 K and 39 emu/g (1.66 μB/f.u.) for Co1.7Fe0.3VGa, respectively, but the maximum entropy change remained almost insensitive to Fe concentration for x ≤ 0.2, the highest value being 3.3 J/kgK at 7 T for Co1.85Fe0.15VGa. First-principle calculations show that Co2VGa retains its half-metallic band structure until at least 30% of the cobalt atoms are replaced by Fe atoms. The wide operating temperature window near room temperature and the lack of thermal and magnetic hysteresis are the interesting features of these materials for application in room-temperature magnetic refrigeration.

Multifunctional Single-Phase Photocatalysts: Extended Near Infrared Photoactivity and Reliable Magnetic Recyclability

NASA Astrophysics Data System (ADS)

Li, Xiaoning; Zhu, Zhu; Li, Feng; Huang, Yan; Hu, Xiang; Huang, Haoliang; Peng, Ranran; Zhai, Xiaofang; Fu, Zhengping; Lu, Yalin

2015-10-01

A practical photocatalyst should be able to integrate together various functions including the extended solar conversion, a feasible and economic recyclability, and above the room temperature operation potential, et al., in order to fulfill the spreading application needs in nowadays. In this report, a multifunctional single-phase photocatalyst which possesses a high photoactivity extended into the near infrared region, an easy magnetic recyclability and the high temperature stability was developed by doping Co into a new layer-structured Bi7Fe3Ti3O21 material. Light absorption and photocatalytic activity of the resulted Bi7Fe3-xCoxTi3O21 photocatalyst were extended to the long wavelength as far as 800 nm. Its strong ferromagnetism above the room temperature enables the nanopowders fully recyclable in viscous solutions simply with a magnet bar in an experimental demonstration. Furthermore, such photoactivity and magnetic recyclability were heavily tested under high-temperature and high-viscosity conditions, which was intended to simulate the actual industrial environments. This work brings the bright light to a full availability of a new multifunctional photocatalyst, via integrating the much enhanced ferromagnetic, ferroelectric, optoelectronic properties, most importantly, into a single-phase structure.

Optimization of single crystals of solid electrolytes with tysonite-type structure (LaF3) for conductivity at 293 K: 2. Nonstoichiometric phases R 1- y M y F3- y ( R = La-Lu, Y; M = Sr, Ba)

NASA Astrophysics Data System (ADS)

Sorokin, N. I.; Sobolev, B. P.; Krivandina, E. A.; Zhmurova, Z. I.

2015-01-01

Single crystals of fluorine-conducting solid electrolytes R 1 - y Sr y F3 - y and R 1 - y Ba y F3 - y ( R = La-Lu, Y) with a tysonite-type structure (LaF3) have been optimized for room-temperature conductivity σ293 K. The optimization is based on high-temperature measurements of σ( T) in two-component nonstoichiometric phases R 1 - y M y F3 - y ( M = Sr, Ba) as a function of the MF2 content. Optimization for thermal stability is based on studying the phase diagrams of MF2- RF3 systems ( M = Sr, Ba) and the behavior of nonstoichiometric crystals upon heating when measuring temperature dependences σ( T). Single crystals of many studied R 1 - y Sr y F3 - y and R 1 - y Ba y F3 - y phases have σ293 K values large enough to use these materials in solid-state electrochemical devices (chemical sensors, fluorine-ion batteries, accumulators, etc.) operating at room temperature.

Eu3+-doped (Y0.5La0.5)2O3: new nanophosphor with the bixbyite cubic structure

NASA Astrophysics Data System (ADS)

Đorđević, Vesna; Nikolić, Marko G.; Bartova, Barbora; Krsmanović, Radenka M.; Antić, Željka; Dramićanin, Miroslav D.

2013-01-01

New red sesquioxide phosphor, Eu3+-doped (Y0.5La0.5)2O3, was synthesized in the form of nanocrystalline powder with excellent structural ordering in cubic bixbyite-type, and with nanoparticle sizes ranging between 10 and 20 nm. Photoluminescence measurements show strong, Eu3+ characteristic, red emission ( x = 0.66 and y = 0.34 CIE color coordinates) with an average 5D0 emission lifetime of about 1.3 ms. Maximum splitting of the 7F1 manifold of the Eu3+ ion emission behaves in a way directly proportional to the crystal field strength parameter, and experimental results show perfect agreement with theoretical values for pure cubic sesquioxides. This could be used as an indicator of complete dissolution of Y2O3 and La2O3, showing that (Y0.5La0.5)2O3:Eu3+ behaves as a new bixbyite structure oxide, M2O3, where M acts as an ion having average ionic radius of constituting Y3+ and La3+. Emission properties of this new phosphor were documented with detailed assignments of Eu3+ energy levels at 10 K and at room temperature. Second order crystal field parameters were found to be B 20 = -66 cm-1 and B 22 = -665 cm-1 at 10 K and B 20 = -78 cm-1 and B 22 = -602 cm-1 at room temperature, while for the crystal field strength the value of 1495 cm-1 was calculated at 10 K and 1355 cm-1 at room temperature.

Structural and optical studies of nitrogen incorporation into GaSb-based GaInSb quantum wells

NASA Astrophysics Data System (ADS)

Nair, Hari P.; Crook, Adam M.; Yu, Kin M.; Bank, Seth R.

2012-01-01

We investigate the incorporation of nitrogen into (Ga,In)Sb grown on GaSb and report room temperature photoluminescence from GaInSb(N) quantum wells. X-ray diffraction and channeling nuclear reaction analysis, together with Rutherford backscattering, were employed to identify the optimal molecular beam epitaxial growth conditions that minimized the incorporation of non-substitutional nitrogen into GaNSb. Consistent with this hypothesis, GaInSb(N) quantum wells grown under the conditions that minimized non-substitutional nitrogen exhibited room temperature photoluminescence, indicative of significantly improved radiative efficiency. Further development of this material system could enable type-I laser diodes emitting throughout the (3-5 μm) wavelength range.

Defect types and room temperature ferromagnetism in N-doped rutile TiO2 single crystals

NASA Astrophysics Data System (ADS)

Qin, Xiu-Bo; Li, Dong-Xiang; Li, Rui-Qin; Zhang, Peng; Li, Yu-Xiao; Wang, Bao-Yi

2014-06-01

The magnetic properties and defect types of virgin and N-doped TiO2 single crystals are probed by superconducting quantum interference device (SQUID), X-ray photoelectron spectroscopy (XPS), and positron annihilation analysis (PAS). Upon N doping, a twofold enhancement of the saturation magnetization is observed. Apparently, this enhancement is not related to an increase in oxygen vacancy, rather to unpaired 3d electrons in Ti3+, arising from titanium vacancies and the replacement of O with N atoms in the rutile structure. The production of titanium vacancies can enhance the room temperature ferromagnetism (RTFM), and substitution of O with N is the onset of ferromagnetism by inducing relatively strong ferromagnetic ordering.

Alternating current conduction studies on polypyrrole-iron nanocomposite at room temperature

NASA Astrophysics Data System (ADS)

Kumar, T. G. Naveen; Megha, R.; Revanasiddappa, M.; Ravikiran, Y. T.; Kumari, S. C. Vijaya

2018-05-01

In the present work, Polypyrrole (PPy) and Polypyrrole-Iron (PPy-Fe) nanocomposite were synthesized separately by chemical polymerisation method and then they were structurally characterised by Fourier transform infrared spectroscopy (FTIR) and Transmission electron microscopy (TEM) techniques. The alternate current (AC) response characteristics at room temperature of PPy and the composite were comparatively studied in the frequency range 100Hz-1MHz. The real part of conductivities of both PPy and the composite were interpreted as power law of frequency and the frequency exponent s was found to lie in the range 0< s<1 in both the cases. The nanocomposite has shown significant improvement in conductivity as compared to PPy.

Engineering giant magnetic anisotropy in single-molecule magnets by dimerizing heavy transition-metal atoms

NASA Astrophysics Data System (ADS)

Qu, Jiaxing; Hu, Jun

2018-05-01

The search for single-molecule magnets with large magnetic anisotropy energy (MAE) is essential for the development of molecular spintronics devices for use at room temperature. Through systematic first-principles calculations, we found that an Os–Os or Ir–Ir dimer embedded in the (5,5‧-Br2-salophen) molecule gives rise to a large MAE of 41.6 or 51.4 meV, respectively, which is large enough to hold the spin orientation at room temperature. Analysis of the electronic structures reveals that the top Os and Ir atoms play the most important part in the total spin moments and large MAEs of the molecules.

Solubilization and spore recovery from silicone polymers. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Hsiao, Y. C.

1974-01-01

A non-sporicidal technique for solvent degradation of cured silicone polymers was developed which involves chemical degradation of cured silicone polymers by amine solvents at room temperature. Substantial improvements were obtained in the recovery of seeded spores from room temperature cured polymers as compared to the standard recovery procedures, which indicates that the curing process is not sufficiently exothermic to reduce spore viability. The dissolution reaction of cured silicone polymers whith amine solvents is proposed to occur by bimolecular nucleophilic displacement. The chemical structure of silicone polymers was determined by spectroscopic methods. The phenyl to methyl ratio, R/Si ratio, molecular weight, and hydroxyl content of the silicone resins were determined.

Electrically pumped 1.3 microm room-temperature InAs/GaAs quantum dot lasers on Si substrates by metal-mediated wafer bonding and layer transfer.

PubMed

Tanabe, Katsuaki; Guimard, Denis; Bordel, Damien; Iwamoto, Satoshi; Arakawa, Yasuhiko

2010-05-10

An electrically pumped InAs/GaAs quantum dot laser on a Si substrate has been demonstrated. The double-hetero laser structure was grown on a GaAs substrate by metal-organic chemical vapor deposition and layer-transferred onto a Si substrate by GaAs/Si wafer bonding mediated by a 380-nm-thick Au-Ge-Ni alloy layer. This broad-area Fabry-Perot laser exhibits InAs quantum dot ground state lasing at 1.31 microm at room temperature with a threshold current density of 600 A/cm(2). (c) 2010 Optical Society of America.

Room-temperature optically pumped laser emission from a-plane GaN with high optical gain characteristics

NASA Astrophysics Data System (ADS)

Kuokstis, E.; Chen, C. Q.; Yang, J. W.; Shatalov, M.; Gaevski, M. E.; Adivarahan, V.; Khan, M. Asif

2004-04-01

Photoluminescence (PL) and optical gain (OG) spectra of a-plane GaN layers have been analyzed over a wide range of excitation intensities. The samples were fully coalesced layers grown by metalorganic chemical vapor deposition over r-plane sapphire substrates using epitaxial layer overgrowth (ELOG) and selective area lateral epitaxy (SALE) procedures. ELOG and SALE a-plane samples showed a strong stimulated emission line in backscattering-geometry PL spectra along with extremely high OG coefficient values (in SALE samples more than 2000 cm-1). Structures prepared with natural cleaved facet cavities based on these films were used to demonstrate optically pumped room-temperature lasing.

Surface tension anomalies in room temperature ionic liquids-acetone solutions

NASA Astrophysics Data System (ADS)

Abe, Hiroshi; Murata, Keisuke; Kiyokawa, Shota; Yoshimura, Yukihiro

2018-05-01

Surface tension anomalies were observed in room temperature ionic liquid (RTIL)-acetone solutions. The RTILs are 1-alkyl-3-methylimidazorium iodide with [Cnmim][I] in a [Cnmim][I]-x mol% acetone. The maximum value of the surface tension appeared at 40 mol% acetone, although density decreased monotonically with an increase in acetone concentration. A small alkyl chain length effect of the Cnmim+ cations was observed in the surface tension. By the Gibbs adsorption isotherm, it was found that I- anion-mediated surface structure became dominant above 40 mol%. In the different [Cnmim][TFSI]-acetone mixtures, normal decay of the surface tension was observed on the acetone concentration scale, where TFSI- is bis(trifluoromethanesulfonyl)imide.

Transformation of multiwall carbon nanotubes to onions with layers cross-linked by sp3 bonds under high pressure and shear deformation

NASA Astrophysics Data System (ADS)

Pankov, A. M.; Bredikhina, A. S.; Kulnitskiy, B. A.; Perezhogin, I. A.; Skryleva, E. A.; Parkhomenko, Yu. N.; Popov, M. Yu.; Blank, V. D.

2017-08-01

A pressure-induced phase transition of multiwall carbon nanotubes (MWNT) to a new structure at room temperature is studied using a shear diamond anvil cell, X-ray photoelectron spectra (XPS), transmission electron microscope (TEM) and Raman procedures. We observe a cardinal pressure-induced change in the nanoparticles shape from multi-shell tubes to multi-shell spheres. MWNT transforms to onions with layers cross-linked by sp3 bonds under the 45-65 GPa compressive stress combined with shear deformation at room temperature. TEM and XPS results show that about 40% of the carbon atoms in the new phase are sp3-bounded.