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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Monocarbon cationic cluster yields from N{sub 2}/CH{sub 4} mixtures embedded in He nanodroplets and their calculated binding energies

The formation of monocarbon cluster ions has been investigated by electron ionization mass spectrometry of cold helium nanodroplets doped with nitrogen/methane mixtures. Ion yields for two groups of clusters, CH{sub m}N{sub 2}{sup +} or CH{sub m}N{sub 4}{sup +}, were determined for mixtures with different molecular ratios of CH{sub 4}. The possible geometrical structures of these clusters were analyzed using electronic structure computations. Little correlation between the ion yields and the associated binding energies has been observed indicating that in most cases kinetic control is more important than thermodynamic control for forming the clusters.

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

Microcantilevers with embedded accelerometers for dynamic atomic force microscopy

The measurement of the intermittent interaction between an oscillating nanotip and the sample surface is a key challenge in dynamic Atomic Force Microscopy (AFM). Accelerometers integrated onto AFM cantilevers can directly measure this interaction with minimal cantilever modification but have been difficult to realize. Here, we design and fabricate high frequency bandwidth accelerometers on AFM cantilevers to directly measure the tip acceleration in commercial AFM systems. We demonstrate a simple way of calibrating such accelerometers and present experiments using amplitude modulated AFM on freshly cleaved mica samples in water to study the response of the accelerometer.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Layer-by-layer charging in non-volatile memory devices using embedded sub-2 nm platinum nanoparticles

In this work, we demonstrate multi-level operation of a non-volatile memory metal oxide semiconductor capacitor by controlled layer-by-layer charging of platinum nanoparticle (PtNP) floating gate devices with defined gate voltage bias ranges. The device consists of two layers of ultra-fine, sub-2 nm PtNPs integrated between Al{sub 2}O{sub 3} tunneling and separation layers. PtNP size and interparticle distance were varied to control the particle self-capacitance and associated Coulomb charging energy. Likewise, the tunneling layer thicknesses were also varied to control electron tunneling to the first and second PtNP layers. The final device configuration with optimal charging behavior and multi-level programming was attained with a 3 nm Al{sub 2}O{sub 3} initial tunneling layer, initial PtNP layer with particle size 0.54 ± 0.12 nm and interparticle distance 4.65 ± 2.09 nm, 3 nm Al{sub 2}O{sub 3} layer to separate the PtNP layers, and second particle layer with 1.11 ± 0.28 nm PtNP size and interparticle distance 2.75 ± 1.05 nm. In this device, the memory window of the first PtNP layer saturated over a programming bias range of 7 V to 14 V, after which the second PtNP layer starts charging, exhibiting a multi-step memory window with layer-by-layer charging.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A low thermal impact annealing process for SiO{sub 2}-embedded Si nanocrystals with optimized interface quality

Silicon nanocrystals (Si NCs) for 3rd generation photovoltaics or optoelectronic applications can be produced by several industrially compatible physical or chemical vapor deposition technologies. A major obstacle for the integration into a fabrication process is the typical annealing to form and crystallize these Si quantum dots (QDs) which involves temperatures ≥1100 °C for 1 h. This standard annealing procedure allows for interface qualities that correspond to more than 95% dangling bond defect free Si NCs. We study the possibilities to use rapid thermal annealing (RTA) and flash lamp annealing to crystallize the Si QDs within seconds or milliseconds at high temperatures. The Si NC interface of such samples exhibits huge dangling bond defect densities which makes them inapplicable for photovoltaics or optoelectronics. However, if the RTA high temperature annealing is combined with a medium temperature inert gas post-annealing and a H{sub 2} passivation, luminescent Si NC fractions of up to 90% can be achieved with a significantly reduced thermal load. A new figure or merit, the relative dopant diffusion length, is introduced as a measure for the impact of a Si NC annealing procedure on doping profiles of device structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Titanium embedded cage structure formation in Al{sub n}Ti{sup +} clusters and their interaction with Ar

Recently, Ar physisorption was used as a structural probe for the location of the Ti dopant atom in aluminium cluster cations, Al{sub n}Ti{sup +} [Lang et al., J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. As an experiment result, the lack of Ar complexes for n > n{sub c} determines the cluster size for which the Ti atom is located inside of an Al cage. To elucidate the decisive factors for the formation of endohedrally Al{sub n}Ti{sup +}, experimentalists proposed detailed computational studies as indispensable. In this work, we investigated, using the density functional theory, the structural and electronic properties of singly titanium doped cationic clusters, Al{sub n}Ti{sup +} (n = 16–21) as well as the adsorption of an Ar atom on them. The first endohedral doped cluster, with Ti encapsulated in a fcc-like cage skeleton, appears at n{sub c} = 21, which is the critical number consistent with the exohedral-endohedral transition experimentally observed. At this critical size the non-crystalline icosahedral growth pattern, related to the pure aluminium clusters, with the Ti atom in the surface, changes into a endohedral fcc-like pattern. The map of structural isomers, relative energy differences, second energy differences, and structural parameters were determined and analyzed. Moreover, we show the critical size depends on the net charge of the cluster, being different for the cationic clusters (n{sub c} = 21) and their neutral counterparts (n{sub c} = 20). For the Al {sub n} Ti {sup +} · Ar complexes, and for n < 21, the preferred Ar adsorption site is on top of the exohedral Ti atom, with adsorption energy in very good agreement with the experimental value. Instead, for n = 21, the Ar adsorption occurs on the top an Al atom with very low absorption energy. For all sizes the geometry of the Al{sub n}Ti{sup +} clusters keeps unaltered in the Ar-cluster complexes. This fact indicates that Ar adsorption does not influence the cluster structure, providing support to the experimental technique used. For n{sub c} = 21, the smallest size of endohedral Ti doped cationic clusters, the Ar binding energy decreases drastically, whereas the Ar-cluster distance increases substantially, point to Ar physisorption, as assumed by the experimentalists. Calculated Ar adsorption energies agree well with available experimental binding energies.

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

Morphology and properties of a hybrid organic-inorganic system: Al nanoparticles embedded into CuPc thin film

The evolution of the morphology and the electronic structure of the hybrid organic-inorganic system composed of aluminum nanoparticles (NPs) distributed in an organic semiconductor matrix—copper phthalocyanine (CuPc)—as a function of nominal aluminum content was studied by transmission electron microscopy and by photoemission spectroscopy methods. The aluminum atoms deposited onto the CuPc surface diffuse into the organic matrix and self-assemble to NPs in a well-defined manner with a narrow diameter distribution, which depends on the amount of aluminum that is evaporated onto the CuPc film. We find clear evidence of a charge transfer from Al to CuPc and we have been able to determine the lattice sites where Al ions sit. The finally at high coverage about 64 Å the formation of metallic aluminum overlayer on CuPc thin film takes place.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Nonlinear optical response of semiconductor-nanocrystals-embedded photonic band gap structure

Colloidal CdSe/ZnS core/shell nanocrystals (NCs), which were dispersed in SiO{sub 2} sol, were utilized to fabricate a SiO{sub 2}:NCs/TiO{sub 2} all-dielectric photonic band gap (PBG) structure. The third-order nonlinear refractive index (n{sub 2}) of the PBG structure was nearly triple of that of the SiO{sub 2}:NCs film due to the local field enhancement in the PBG structure. The photoinduced change in refractive index (Δn) could shift the PBG band edge, so the PBG structure would show significant transmission modification, whose transmission change was ∼17 folds of that of the SiO{sub 2}:NCs film. Under excitation of a 30 GW/cm{sup 2} femtosecond laser beam, a transmission decrease of 80% was realized.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Conversion of above- and below-bandgap photons via InAs quantum dot media embedded into GaAs solar cell

Quantum dots (QDs) provide photovoltaic conversion of below-bandgap photons due to multistep electron transitions. QDs also increase conversion efficiency of the above-bandgap photons due to extraction of electrons from QDs via Coulomb interaction with hot electrons excited by high-energy photons. Nanoscale potential profile (potential barriers) and nanoscale band engineering (AlGaAs atomically thin barriers) allow for suppression of photoelectron capture to QDs. To study these kinetic effects and to distinguish them from the absorption enhancement due to light scattering on QDs, we investigate long, 3-μm base GaAs devices with various InAs QD media with 20 and 40 QD layers. Quantum efficiency measurements show that, at least at low doping, the multistep processes in QD media are strongly affected by the wetting layer (WL). The QD media with WLs provide substantial conversion of below-bandgap photons and for devices with 40 QD layers the short circuit current reaches 29.2 mA/cm{sup 2}. The QD media with band-engineered AlGaAs barriers and reduced wetting layers (RWL) enhance conversion of high-energy photons and decrease the relaxation (thermal) losses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets

Methanol is one of the simplest molecules that undergo torsional oscillations, and so it has been extensively studied in the gas phase by various spectroscopic techniques. At 300 K, a large number of rotational, torsional, and vibrational energy levels is populated, and this makes for a rather complicated spectrum, which is still not fully understood. It is expected that in going from 300 K to 0.4 K (the temperature of helium nanodroplets) the population distribution of methanol will mainly collapse into two states; the J{sub K} = 0{sub 0} state for the A{sub 1} nuclear spin symmetry species (with I{sub CH{sub 3}} = 3/2), and the J{sub K} = 1{sub −1} state for the E species (I{sub CH{sub 3}} = 1/2). This results in a simplified spectrum that consists of narrow a-type (ΔK = 0) lines and broader b- and c-type (ΔK = ±1) lines. We have recorded the rotovibrational spectrum of CH{sub 3}OH in the OH stretching, CH{sub 3} stretching and bending, CH{sub 3} rocking, and CO stretching regions, and have firmly assigned five bands (v{sub 1}, v{sub 2}, v{sub 3}, v{sub 7}, and v{sub 8}), and tentatively assigned five others (v{sub 9}, 2v{sub 4}, v{sub 4} + v{sub 10}, 2v{sub 10}, and v{sub 4} + v{sub 5}). To our knowledge, the transitions we have assigned within the v{sub 4} + v{sub 10}, 2v{sub 10}, and v{sub 4} + v{sub 5} bands have not yet been assigned in the gas phase, and we hope that considering the very small “matrix” shift in helium nanodroplets (<1 cm{sup −1} for most subband origins of CH{sub 3}OH), those made here can aid in their gas phase identification. Microwave-infrared double resonance spectroscopy was used to confirm the initially tentative a-type infrared assignments in the OH stretching (v{sub 1}) band of A{sub 1} species methanol, in addition to revealing “warm” b-type lines. From a rotovibrational analysis, the B rotational constant is found to be reduced quite significantly (56%) with respect to the gas phase, and the torsional tunneling splittings are relatively unaffected and are at most reduced by 16%. While most rovibrational peaks are Lorentzian shaped, and those which are significantly perturbed by vibrational coupling in the gas phase are additionally broadened, the narrowest ΔJ = +1 peaks are asymmetric, and a skew-type analysis suggests that the response time of the helium solvent upon excitation is of the order of 1 ns.

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

Observations on size confinement effect in B-C-N nanoparticles embedded in mesoporous silica channels

Fluorescent B-C-N/silica nanoparticles were synthesized by solution impregnation method. Effect of B-C-N particle size on the optical properties was investigated by varying the silica pore sizes. Formation of B-C-N nanoparticles within the mesoporous matrix is confirmed by x-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. Furthermore, a remarkable blue-shift in emission peak centres with decreasing pore size in conjugation with band gap modification, ascribed to the size confinement effect. A detailed analysis of experimental results by theoretically defined confinement models demonstrates that the B-C-N nanoparticles in the size range of 3–13 nm falls within the confinement regime. This work demonstrated the experimental evidence of the size confinement effect in smaller size B-C-N nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Synthesis and properties of ferromagnetic nanostructures embedded within a high-quality crystalline silicon matrix via ion implantation and nanocavity assisted gettering processes

Integrating magnetic functionalities with silicon holds the promise of developing, in the most dominant semiconductor, a paradigm-shift information technology based on the manipulation and control of electron spin and charge. Here, we demonstrate an ion implantation approach enabling the synthesis of a ferromagnetic layer within a defect free Si environment by exploiting an additional implant of hydrogen in a region deep below the metal implanted layer. Upon post-implantation annealing, nanocavities created within the H-implanted region act as trapping sites for gettering the implanted metal species, resulting in the formation of metal nanoparticles in a Si region of excellent crystal quality. This is exemplified by the synthesis of magnetic nickel nanoparticles in Si implanted with H{sup +} (range: ∼850 nm; dose: 1.5 × 10{sup 16 }cm{sup −2}) and Ni{sup +} (range: ∼60 nm; dose: 2 × 10{sup 15 }cm{sup −2}). Following annealing, the H implanted regions populated with Ni nanoparticles of size (∼10–25 nm) and density (∼10{sup 11}/cm{sup 2}) typical of those achievable via conventional thin film deposition and growth techniques. In particular, a maximum amount of gettered Ni atoms occurs after annealing at 900 °C, yielding strong ferromagnetism persisting even at room temperature, as well as fully recovered crystalline Si environments adjacent to these Ni nanoparticles. Furthermore, Ni nanoparticles capsulated within a high-quality crystalline Si layer exhibit a very high magnetic switching energy barrier of ∼0.86 eV, an increase by about one order of magnitude as compared to their counterparts on a Si surface or in a highly defective Si environment.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Fluctuating hydrodynamics of multicomponent membranes with embedded proteins

A simulation method for the dynamics of inhomogeneous lipid bilayer membranes is presented. The membrane is treated using stochastic Saffman-Delbrück hydrodynamics, coupled to a phase-field description of lipid composition and discrete membrane proteins. Multiple applications are considered to validate and parameterize the model. The dynamics of membrane composition fluctuations above the critical point and phase separation dynamics below the critical point are studied in some detail, including the effects of adding proteins to the mixture.

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

Visualization of the operational space of edge-localized modes through low-dimensional embedding of probability distributions

Information visualization aimed at facilitating human perception is an important tool for the interpretation of experiments on the basis of complex multidimensional data characterizing the operational space of fusion devices. This work describes a method for visualizing the operational space on a two-dimensional map and applies it to the discrimination of type I and type III edge-localized modes (ELMs) from a series of carbon-wall ELMy discharges at JET. The approach accounts for stochastic uncertainties that play an important role in fusion data sets, by modeling measurements with probability distributions in a metric space. The method is aimed at contributing to physical understanding of ELMs as well as their control. Furthermore, it is a general method that can be applied to the modeling of various other plasma phenomena as well.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Positron impact excitations of hydrogen atom embedded in weakly coupled plasmas: Formation of Rydberg atoms

Formation of Rydberg atoms due to 1s→nlm excitations of hydrogen, for arbitrary n, l, m, by positron impact in weakly coupled plasma has been investigated using a distorted-wave theory in the momentum space. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. Making use of a simple variationally determined wave function for the hydrogen atom, it has been possible to obtain the distorted-wave scattering amplitude in a closed analytical form. A detailed study has been made on the effects of plasma screening on the differential and total cross sections in the energy range 20–300 eV of incident positron. For the unscreened case, our results agree nicely with some of the most accurate results available in the literature. To the best of our knowledge, such a study on the differential and total cross sections for 1s→nlm inelastic positron-hydrogen collisions for arbitrary n, l, m in weakly coupled plasmas is the first reported in the literature.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Highly uniform, multi-stacked InGaAs/GaAs quantum dots embedded in a GaAs nanowire

We demonstrate a highly uniform, dense stack of In{sub 0.22}Ga{sub 0.78}As/GaAs quantum dot (QD) structures in a single GaAs nanowire (NW). The size (and hence emission energy) of individual QD is tuned by careful control of the growth conditions based on a diffusion model of morphological evolution of NWs and optical characterization. By carefully tailoring the emission energies of individual QD, dot-to-dot inhomogeneous broadening of QD stacks in a single NW can be as narrow as 9.3 meV. This method provides huge advantages over traditional QD stack using a strain-induced Stranski-Krastanow growth scheme. We show that it is possible to fabricate up to 200 uniform QDs in single GaAs NWs using this growth technique without degradation of the photoluminescence intensity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

A 32-channel photon counting module with embedded auto/cross-correlators for real-time parallel fluorescence correlation spectroscopy

Fluorescence correlation spectroscopy (FCS) is a well-established technique to study binding interactions or the diffusion of fluorescently labeled biomolecules in vitro and in vivo. Fast FCS experiments require parallel data acquisition and analysis which can be achieved by exploiting a multi-channel Single Photon Avalanche Diode (SPAD) array and a corresponding multi-input correlator. This paper reports a 32-channel FPGA based correlator able to perform 32 auto/cross-correlations simultaneously over a lag-time ranging from 10 ns up to 150 ms. The correlator is included in a 32 × 1 SPAD array module, providing a compact and flexible instrument for high throughput FCS experiments. However, some inherent features of SPAD arrays, namely afterpulsing and optical crosstalk effects, may introduce distortions in the measurement of auto- and cross-correlation functions. We investigated these limitations to assess their impact on the module and evaluate possible workarounds.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Growth of silicon quantum dots by oxidation of the silicon nanocrystals embedded within silicon carbide matrix

A moderately low temperature (≤800 °C) thermal processing technique has been described for the growth of the silicon quantum dots (Si-QD) within microcrystalline silicon carbide (μc-SiC:H) dielectric thin films deposited by plasma enhanced chemical vapour deposition (PECVD) process. The nanocrystalline silicon grains (nc-Si) present in the as deposited films were initially enhanced by aluminium induced crystallization (AIC) method in vacuum at a temperature of T{sub v} = 525 °C. The samples were then stepwise annealed at different temperatures T{sub a} in air ambient. Analysis of the films by FTIR and XPS reveal a rearrangement of the μc-SiC:H network has taken place with a significant surface oxidation of the nc-Si domains upon annealing in air. The nc-Si grain size (D{sub XRD}) as calculated from the XRD peak widths using Scherrer formula was found to decrease from 7 nm to 4 nm with increase in T{sub a} from 250 °C to 800 °C. A core shell like structure with the nc-Si as the core and the surface oxide layer as the shell can clearly describe the situation. The results indicate that with the increase of the annealing temperature in air the oxide shell layer becomes thicker and the nc-Si cores become smaller until their size reduced to the order of the Si-QDs. Quantum confinement effect due to the SiO covered nc-Si grains of size about 4 nm resulted in a photoluminescence peak due to the Si QDs with peak energy at 1.8 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Embedded image processing engine using ARM cortex-M4 based STM32F407 microcontroller

Due to advancement in low cost, easily available, yet powerful hardware and revolution in open source software, urge to make newer, more interactive machines and electronic systems have increased manifold among engineers. To make system more interactive, designers need easy to use sensor systems. Giving the boon of vision to machines was never easy, though it is not impossible these days; it is still not easy and expensive. This work presents a low cost, moderate performance and programmable Image processing engine. This Image processing engine is able to capture real time images, can store the images in the permanent storage and can perform preprogrammed image processing operations on the captured images.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗