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Huang, Yu

Publications and source records attributed to Huang, Yu.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Size-dependent phase transition in methylammonium lead iodide perovskite microplate crystals

Methylammonium lead iodide perovskite has attracted considerable recent interest for solution processable solar cells and other optoelectronic applications. The orthorhombic-to-tetragonal phase transition in perovskite can significantly alter its optical, electrical properties and impact the corresponding applications. Here, we report a systematic investigation of the size-dependent orthorhombic-to-tetragonal phase transition using a combined temperature-dependent optical, electrical transport and transmission electron microscopy study. Our studies of individual perovskite microplates with variable thicknesses demonstrate that the phase transition temperature decreases with reducing microplate thickness. The sudden decrease of mobility around phase transition temperature and the presence of hysteresis loops in the temperature-dependent mobility confirm that the orthorhombic-to-tetragonal phase transition is a first-order phase transition. Lastly, our findings offer significant fundamental insight on the temperature-and size-dependent structural, optical and charge transport properties of perovskite materials, and can greatly impact future exploration of novel electronic and optoelectronic devices from these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Wafer-scale growth of large arrays of perovskite microplate crystals for functional electronics and optoelectronics

Methylammonium lead iodide perovskite has attracted intensive interest for its diverse optoelectronic applications. However, most studies to date have been limited to bulk thin films that are difficult to implement for integrated device arrays because of their incompatibility with typical lithography processes. We report the first patterned growth of regular arrays of perovskite microplate crystals for functional electronics and optoelectronics. We show that large arrays of lead iodide microplates can be grown from an aqueous solution through a seeded growth process and can be further intercalated with methylammonium iodide to produce perovskite crystals. Structural and optical characterizations demonstrate that the resulting materials display excellent crystalline quality and optical properties. We further show that perovskite crystals can be selectively grown on prepatterned electrode arrays to create independently addressable photodetector arrays and functional field effect transistors. Furthermore, the ability to grow perovskite microplates and to precisely place them at specific locations offers a new material platform for the fundamental investigation of the electronic and optical properties of perovskite materials and opens a pathway for integrated electronic and optoelectronic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2015

High-performance transition metal-doped Pt 3 Ni octahedra for oxygen reduction reaction

Bimetallic platinum-nickel (Pt-Ni) nanostructures represent an emerging class of electrocatalysts for oxygen reduction reaction (ORR) in fuel cells, but practical applications have been limited by catalytic activity and durability. We surface-doped Pt 3 Ni octahedra supported on carbon with transition metals, termed M-Pt 3 Ni/C, where M is vanadium, chromium, manganese, iron, cobalt, molybdenum (Mo), tungsten, or rhenium. The Mo-Pt 3 Ni/C showed the best ORR performance, with a specific activity of 10.3 mA/cm2 and mass activity of 6.98 A/mgPt, which are 81- and 73-fold enhancements compared with the commercial Pt/C catalyst (0.127 mA/cm 2 and 0.096 A/mg Pt ). In conclusion, theoretical calculations suggest that Mo prefers subsurface positions near the particle edges in vacuum and surface vertex/edge sites in oxidizing conditions, where it enhances both the performance and the stability of the Pt3Ni catalyst.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2015

ATTENUATION OF CORONAL MAGNETIC FIELDS IN SOLAR MICROWAVE BURSTS

Based on the observed data by the Nobeyama Radio Observatory and the nonthermal gyrosynchrotron theory, the calculated magnetic field in a loop-like radio source of the 2001 October 23 flare attenuates from hundreds to tens of Gauss, except in the region with very weak magnetic fields. Meanwhile, the viewing angle between the magnetic field and line of sight has a similar attenuation from tens to around ten degrees, implying that the transverse magnetic component attenuates much faster than the longitudinal one. All of these results can be understood by the magnetic energy release process in solar flares. Moreover, the column density of nonthermal electrons decreases from 10{sup 9−10} to 10{sup 7−8} cm{sup −2} during the flare, except in the region with very weak magnetic fields, where its value is larger than that with strong magnetic fields due to the mirroring effect. The calculated error and harmonic number of gyrofrequency better suit the region with strong magnetic fields.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Enhanced photocatalytic hydrogen evolution efficiency using hollow microspheres of (CuIn) x Zn 2(1-x) S 2 solid solutions

Hollow spheres of multicomponent (CuIn) x Zn 2(1-x) S 2 solid solutions have been rapidly synthesized by a salt-assisted aerosol decomposition method. (CuIn) 0.2 Zn 1.6 S 2 hollow spheres with a band gap of 2.53 eV exhibited an excellent and stable photocatalytic activity of 360 μmol h-1 (50 mg photocatalysts) for hydrogen evolution from aqueous solutions containing sacrificial reagents (SO 3 2- and S 2- ) under visible light (λ ≥ 420 nm) due to the well-crystallized microspheres and mesoporous structures. H2 evolution rate of the (CuIn) 0.2 Zn 1.6 S 2 hollow spheres reached as high as 57 μmol h -1 (50 mg photocatalysts) even without Ru loading.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Characterization of hot-pressed short ZrO{sub 2} fiber toughened ZrB{sub 2}-based ultra-high temperature ceramics

Two different ZrB{sub 2}-based ultra-high temperature ceramics were produced by hot pressing: ZrB{sub 2} + 20 vol.% SiC particle + 15 vol.% ZrO{sub 2} fiber and ZrB{sub 2} + 20 vol.% SiC whisker + 15 vol.% ZrO{sub 2} fiber. The microstructures were analyzed by using transmission electron microscopy and high-resolution transmission electron microscopy. It was shown that a clean interface without any impurities was identified in ZrB{sub 2}-based hybrid ceramics with SiC whiskers and ZrO{sub 2} fibers, which would significantly improve the toughening mechanism. The results of high-resolution transmission electron microscopy showed that stacking faults in SiC whiskers resulted from an insertion of a (111) layer, which would be one of the main reasons for material anisotropy. However, the interface between the SiC particle and ZrO{sub 2} fiber was found to be ambiguous in ZrB{sub 2}-based hybrid ceramics with SiC particles and ZrO{sub 2} fibers due to the slight reaction. The orientation relationship between t-ZrO{sub 2} and m-ZrO{sub 2} phases obeyed the classical correspondence: (100){sub m}//(100){sub t} and [001]{sub m}//〈001〉{sub t}, which further verified the feasibility of phase transformation toughening mechanism. - Highlights: • ZrB{sub 2}-based ceramics toughened by short ZrO{sub 2} fiber are characterized by TEM and HRTEM. • The orientation relationship of t- and m-ZrO{sub 2} are (100){sub m}//(100){sub t}, [001]{sub m}//〈001〉{sub t} • The clean interface without any impurities leads to improve the toughening mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Metal–semiconductor transition in atomically thin Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8} nanosheets

Two-dimensional layered materials have attracted considerable attention since the discovery of graphene. Here we demonstrate that the layered Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8} (BSCO) can be mechanically exfoliated into single- or few-layer nanosheets. The BSCO nanosheets with four or more layers display bulk metallic characteristics, while the nanosheets with three or fewer layers have a layer-number-dependent semiconducting characteristics. Charge transport in bilayer or trilayer BSCO nanosheets exhibits Mott 2D variable-range-hopping (VRH) conduction throughout 2 K–300 K, while the charge transport in monolayers follows the Mott-VRH law above a crossover temperature of 75 K, and is governed by Efros and Shklovskii-VRH laws below 75 K. Disorder potentials and Coulomb charging both contribute to the transport gap of these nanodevices. Our study reveals a distinct layer number-dependent metal-to-semiconductor transition in a new class of 2D materials, and is of great significance for both fundamental investigations and practical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Anomalous output characteristic shift for the n-type lateral diffused metal-oxide-semiconductor transistor with floating P-top layer

Anomalous output characteristic shift of the n-type lateral diffused metal-oxide-semiconductor transistor with floating P-top layer is investigated. It shows that the linear drain current has obvious decrease when the output characteristic of fresh device is measured for two consecutive times. The charge pumping experiments demonstrate that the decrease is not from hot-carrier degradation. The reduction of cross section area for the current flowing, which results from the squeezing of the depletion region surrounding the P-top layer, is responsible for the shift. Consequently, the current capability of this special device should be evaluated by the second measured output characteristic.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Complex dynamics of a delayed discrete neural network of two nonidentical neurons

In this paper, we discover that a delayed discrete Hopfield neural network of two nonidentical neurons with self-connections and no self-connections can demonstrate chaotic behaviors. To this end, we first transform the model, by a novel way, into an equivalent system which has some interesting properties. Then, we identify the chaotic invariant set for this system and show that the dynamics of this system within this set is topologically conjugate to the dynamics of the full shift map with two symbols. This confirms chaos in the sense of Devaney. Our main results generalize the relevant results of Huang and Zou [J. Nonlinear Sci. 15, 291–303 (2005)], Kaslik and Balint [J. Nonlinear Sci. 18, 415–432 (2008)] and Chen et al. [Sci. China Math. 56(9), 1869–1878 (2013)]. We also give some numeric simulations to verify our theoretical results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Ultralow-threshold laser and blue shift cooperative luminescence in a Yb{sup 3+} doped silica microsphere

An experimental investigation on ultralow threshold laser and blue shift cooperative luminescence (CL) in a Yb{sup 3+} doped silica microsphere (YDSM) with continuous-wave 976 nm laser diode pumping is reported. The experimental results show that the YDSM emits laser oscillation with ultralow threshold of 2.62 μW, and the laser spectrum is modulated by the microsphere morphology characteristics. In addition, blue emission of YDSM is also observed with the increase of pump power, which is supposed to be generated by CL of excited Yb ion-pairs with the absorption of 976 nm photons and Si-O vibration phonons, and the process is explained with an energy level diagram. This property of the blue shift CL with phonons absorption in the Yb{sup 3+}doped microcavity makes it attractive for the application of laser cooling based on anti-Stokes fluorescence emission, if the Yb{sup 3+}doped microcavity made from with low phonon energy host materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Analysis of DOE's Roof Savings Calculator with Comparison to other Simulation Engines

A web-based Roof Savings Calculator (RSC) has been deployed for the Department of Energy as an industry-consensus tool to help building owners, manufacturers, distributors, contractors and researchers easily run complex roof and attic simulations. This tool employs the latest web technologies and usability design to provide an easy input interface to an annual simulation of hour-by-hour, whole-building performance using the world-class simulation tools DOE-2.1E and AtticSim. Building defaults were assigned based on national averages and can provide estimated annual energy and cost savings after the user selects nothing more than building location. In addition to cool reflective roofs, the RSC tool can simulate multiple roof and attic configurations including different roof slopes, above sheathing ventilation, radiant barriers, low-emittance surfaces, HVAC duct location, duct leakage rates, multiple layers of building materials, ceiling and deck insulation levels, and other parameters. A base case and energy-efficient alternative can be compared side-by-side to generate an energy/cost savings estimate between two buildings. The RSC tool was benchmarked against field data for demonstration homes in Ft. Irwin, CA. However, RSC gives different energy savings estimates than previous cool roof simulation tools so more thorough software and empirical validation proved necessary. This report consolidates much of the preliminary analysis for comparison of RSC s projected energy savings to that from other simulation engines.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2014

Comparison of Software Models for Energy Savings from Cool Roofs

A web-based Roof Savings Calculator (RSC) has been deployed for the United States Department of Energy as an industry-consensus tool to help building owners, manufacturers, distributors, contractors and researchers easily run complex roof and attic simulations. This tool employs modern web technologies, usability design, and national average defaults as an interface to annual simulations of hour-by-hour, whole-building performance using the world-class simulation tools DOE-2.1E and AtticSim in order to provide estimated annual energy and cost savings. In addition to cool reflective roofs, RSC simulates multiple roof and attic configurations including different roof slopes, above sheathing ventilation, radiant barriers, low-emittance roof surfaces, duct location, duct leakage rates, multiple substrate types, and insulation levels. A base case and energy-efficient alternative can be compared side-by-side to estimate monthly energy. RSC was benchmarked against field data from demonstration homes in Ft. Irwin, California; while cooling savings were similar, heating penalty varied significantly across different simulation engines. RSC results reduce cool roofing cost-effectiveness thus mitigating expected economic incentives for this countermeasure to the urban heat island effect. This paper consolidates comparison of RSC s projected energy savings to other simulation engines including DOE-2.1E, AtticSim, Micropas, and EnergyPlus, and presents preliminary analyses. RSC s algorithms for capturing radiant heat transfer and duct interaction in the attic assembly are considered major contributing factors to increased cooling savings and heating penalties. Comparison to previous simulation-based studies, analysis on the force multiplier of RSC cooling savings and heating penalties, the role of radiative heat exchange in an attic assembly, and changes made for increased accuracy of the duct model are included.

New, Joshua Ryan↗
DOE OSTI2013

Dehydration processes using membranes with hydrophobic coating

Processes for removing water from organic compounds, especially polar compounds such as alcohols. The processes include a membrane-based dehydration step, using a membrane that has a dioxole-based polymer selective layer or the like and a hydrophilic selective layer, and can operate even when the stream to be treated has a high water content, such as 10 wt % or more. The processes are particularly useful for dehydrating ethanol.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Membrane augmented distillation to separate solvents from water

Processes for removing water from organic solvents, such as ethanol. The processes include distillation to form a rectified overhead vapor, compression of the rectified vapor, and treatment of the compressed vapor by two sequential membrane separation steps.

47 OTHER INSTRUMENTATION↗