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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Coherence of a spin-polarized electron beam emitted from a semiconductor photocathode in a transmission electron microscope

The brightness and interference fringes of a spin-polarized electron beam extracted from a semiconductor photocathode excited by laser irradiation are directly measured via its use in a transmission electron microscope. The brightness was 3.8 × 10{sup 7 }A cm{sup −2 }sr{sup −1} for a 30-keV beam energy with the polarization of 82%, which corresponds to 3.1 × 10{sup 8 }A cm{sup −2 }sr{sup −1} for a 200-keV beam energy. The resulting electron beam exhibited a long coherence length at the specimen position due to the high parallelism of (1.7 ± 0.3) × 10{sup −5 }rad, which generated interference fringes representative of a first-order correlation using an electron biprism. The beam also had a high degeneracy of electron wavepacket of 4 × 10{sup −6}. Due to the high polarization, the high degeneracy and the long coherence length, the spin-polarized electron beam can enhance the antibunching effect.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Invited Article: Autonomous assembly of atomically perfect nanostructures using a scanning tunneling microscope

A major goal of nanotechnology is to develop the capability to arrange matter at will by placing individual atoms at desired locations in a predetermined configuration to build a nanostructure with specific properties or function. The scanning tunneling microscope has demonstrated the ability to arrange the basic building blocks of matter, single atoms, in two-dimensional configurations. An array of various nanostructures has been assembled, which display the quantum mechanics of quantum confined geometries. The level of human interaction needed to physically locate the atom and bring it to the desired location limits this atom assembly technology. Here we report the use of autonomous atom assembly via path planning technology; this allows atomically perfect nanostructures to be assembled without the need for human intervention, resulting in precise constructions in shorter times. We demonstrate autonomous assembly by assembling various quantum confinement geometries using atoms and molecules and describe the benefits of this approach.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Microscopic diamond solid-immersion-lenses fabricated around single defect centers by focused ion beam milling

Recent efforts to define microscopic solid-immersion-lenses (SIL) by focused ion beam milling into diamond substrates that are registered to a preselected single photon emitter are summarized. We show how we determine the position of a single emitter with at least 100 nm lateral and 500 nm axial accuracy, and how the milling procedure is optimized. The characteristics of a single emitter, a Nitrogen Vacancy (NV) center in diamond, are measured before and after producing the SIL and compared with each other. A count rate of 1.0 × 10{sup 6} counts/s is achieved with a [111] oriented NV center.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

A high stability and repeatability electrochemical scanning tunneling microscope

We present a home built electrochemical scanning tunneling microscope (ECSTM) with very high stability and repeatability. Its coarse approach is driven by a closely stacked piezo motor of GeckoDrive type with four rigid clamping points, which enhances the rigidity, compactness, and stability greatly. It can give high clarity atomic resolution images without sound and vibration isolations. Its drifting rates in XY and Z directions in solution are as low as 84 pm/min and 59 pm/min, respectively. In addition, repeatable coarse approaches in solution within 2 mm travel distance show a lateral deviation less than 50 nm. The gas environment can be well controlled to lower the evaporation rate of the cell, thus reducing the contamination and elongating the measurement time. Atomically resolved SO{sub 4}{sup 2−} image on Au (111) work electrode is demonstrated to show the performance of the ECSTM.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Microscopic derivation of open quantum walks

A microscopic derivation of an open quantum walk of a three level system on a two node graph is presented. The explicit form of the 'quantum coin' operators is derived.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Characterization of surface modification in atomic force microscope-induced nanolithography of oxygen deficient La{sub 0.67}Ba{sub 0.33}MnO{sub 3−δ} thin films

We report our studies of the nanolithographic surface modifications induced by an Atomic Force Microscope (AFM) in epitaxial thin films of oxygen deficient Lanthanum Barium Manganese Oxide (La{sub 0.67}Ba{sub 0.33}MnO{sub 3−δ}). The pattern characteristics depend on the tip voltage, tip polarity, voltage duration, tip force, and humidity. We have used Electron Energy Dispersive X-Ray Spectroscopy (EDS) to analyze the chemical changes associated with the surface modifications produced with a negatively biased AFM tip. A significant increase in the oxygen stoichiometry for the patterned regions relative to the pristine film surface is observed. The results also indicate changes in the cation stoichiometry, specifically a decrease in the Lanthanum and Manganese concentrations and an increase in the Barium concentration in the patterned regions.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microscopic properties of degradation-free capped GdN thin films studied by electron spin resonance

The microscopic magnetic properties of high-quality GdN thin films have been investigated by electron spin resonance (ESR) and ferromagnetic resonance (FMR) measurements. Detailed temperature dependence ESR measurements have shown the existence of two ferromagnetic components at lower temperatures, which was not clear from the previous magnetization measurements. The temperature, where the resonance shift occurs for the major ferromagnetic component, seems to be consistent with the Curie temperature obtained from the previous magnetization measurement. On the other hand, the divergence of line width is observed around 57 K for the minor ferromagnetic component. The magnetic anisotropies of GdN thin films have been obtained by the analysis of FMR angular dependence observed at 4.2 K. Combining the X-ray diffraction results, the correlation between the magnetic anisotropies and the lattice constants is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effects of spin diffusion on electron spin relaxation time measured with a time-resolved microscopic photoluminescence technique

We performed measurements at room temperature for a GaAs/AlGaAs multiple quantum well grown on GaAs(110) using a time-resolved microscopic photoluminescence (micro-PL) technique to find what effects spin diffusion had on the measured electron spin relaxation time, τ{sub s}, and developed a method of estimating the spin diffusion coefficient, D{sub s}, using the measured data and the coupled drift-diffusion equations for spin polarized electrons. The spatial nonuniformities of τ{sub s} and the initial degree of electron spin polarization caused by the pump intensity distribution inside the focal spot were taken into account to explain the dependence of τ{sub s} on the measured spot size, i.e., a longer τ{sub s} for a smaller spot size. We estimated D{sub s} as ∼100 cm{sup 2}/s, which is similar to a value reported in the literature. We also provided a qualitative understanding on how spin diffusion lengthens τ{sub s} in micro-PL measurements.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Maximum probability domains for the analysis of the microscopic structure of liquids

We introduce the concept of maximum probability domains (MPDs), developed in the context of the analysis of electronic densities, in the study of the microscopic spatial structures of liquids. The idea of locating a particle in a three dimensional region, by determining the domain where the probability of finding that, and only that, particle is maximum, gives an interesting characterization of the local structure of the liquid. The optimization procedure, required for the search of the domain of maximum probability, is carried out by the implementation of the level set method. Results for a couple of case studies are presented, to illustrate the structure of liquid water at ambient conditions and upon increasing pressure from the point of view of MPDs and to compare the information encoded in the solvation shells of sodium in water with, once again, that extracted from the MPDs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Exchange spring in A1/L1{sub 0} FePt composite and its application in magnetic force microscope

This paper reported fabrication of Fe{sub x}Pt{sub 100-x} films with (001) epitaxy on MgO(100) substrates. The atomic percentage of Fe was changed within the range of x = 10–85 in order to search the optimal atomic ratio for achieving both high and isotropic-like coercivity. It was found that the Fe{sub 60}Pt{sub 40} film exhibited large coercivities exceeding 5 kOe along both in-plane and out-of-plane directions due to the formation of A1/L1{sub 0} FePt composite. A penta-domain model for hard/soft/hard exchange spring system was proposed to interpret the anomalous magnetization behaviors observed in Fe{sub 60}Pt{sub 40} sample. By using Fe{sub 60}Pt{sub 40} as the magnetic coating layer on a probe of magnetic force microscope, the flux changes at a linear density of 1000 kfci could be readily observed at a resolution of ∼13 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Charge collection microscopy of in-situ switchable PRAM line cells in a scanning electron microscope: Technique development and unique observations

An imaging method has been developed based on charge collection in a scanning electron microscope (SEM) that allows discrimination between the amorphous and crystalline states of Phase-change Random Access Memory (PRAM) line cells. During imaging, the cells are electrically connected and can be switched between the states and the resistance can be measured. This allows for electrical characterization of the line cells in-situ in the SEM. Details on sample and measurement system requirements are provided which turned out to be crucial for the successful development of this method. Results show that the amorphous or crystalline state of the line cells can be readily discerned, but the spatial resolution is relatively poor. Nevertheless, it is still possible to estimate the length of the amorphous mark, and also for the first time, we could directly observe the shift of the amorphous mark from one side of the line cell to the other side when the polarity of the applied (50 ns) RESET pulse was reversed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

A subsurface add-on for standard atomic force microscopes

The application of ultrasound in an Atomic Force Microscope (AFM) gives access to subsurface information. However, no commercially AFM exists that is equipped with this technique. The main problems are the electronic crosstalk in the AFM setup and the insufficiently strong excitation of the cantilever at ultrasonic (MHz) frequencies. In this paper, we describe the development of an add-on that provides a solution to these problems by using a special piezo element with a lowest resonance frequency of 2.5 MHz and by separating the electronic connection for this high frequency piezo element from all other connections. In this sense, we support researches with the possibility to perform subsurface measurements with their existing AFMs and hopefully pave also the way for the development of a commercial AFM that is capable of imaging subsurface features with nanometer resolution.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

The ReactorAFM: Non-contact atomic force microscope operating under high-pressure and high-temperature catalytic conditions

An Atomic Force Microscope (AFM) has been integrated in a miniature high-pressure flow reactor for in-situ observations of heterogeneous catalytic reactions under conditions similar to those of industrial processes. The AFM can image model catalysts such as those consisting of metal nanoparticles on flat oxide supports in a gas atmosphere up to 6 bar and at a temperature up to 600 K, while the catalytic activity can be measured using mass spectrometry. The high-pressure reactor is placed inside an Ultrahigh Vacuum (UHV) system to supplement it with standard UHV sample preparation and characterization techniques. To demonstrate that this instrument successfully bridges both the pressure gap and the materials gap, images have been recorded of supported palladium nanoparticles catalyzing the oxidation of carbon monoxide under high-pressure, high-temperature conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Temperature and non-linear response of cantilever-type mechanical oscillators used in atomic force microscopes with interferometric detection

The sensitivity of atomic force microscopes is fundamentally limited by the cantilever temperature, which can be, in principle, determined by measuring its thermal spectrum and applying the equipartition theorem. However, the mechanical response can be affected by the light field inside the cavity of a Fabry-Perot interferometer due to light absorption, radiation pressure, photothermal forces, and laser noise. By evaluating the optomechanical Hamiltonian, we are able to explain the peculiar distance dependence of the mechanical quality factor as well as the appearance of thermal spectra with symmetrical Lorentzian as well as asymmetrical Fano line shapes. Our results can be applied to any type of mechanical oscillator in an interferometer-based detection system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Characteristics of different frequency ranges in scanning electron microscope images

We demonstrate a new approach to characterize the frequency range in general scanning electron microscope (SEM) images. First, pure frequency images are generated from low frequency to high frequency, and then, the magnification of each type of frequency image is implemented. By comparing the edge percentage of the SEM image to the self-generated frequency images, we can define the frequency ranges of the SEM images. Characterization of frequency ranges of SEM images benefits further processing and analysis of those SEM images, such as in noise filtering and contrast enhancement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Apertureless scanning microscope probe as a detector of semiconductor laser emission

An operating semiconductor laser has been studied using a scanning probe microscope. A shift of the resonance frequency of probe that is due to its heating by laser radiation has been analyzed. The observed shift is proportional to the absorbed radiation and can be used to measure the laser near field or its output power. A periodical dependence of the measured signal has been observed as a function of distance between the probe and the surface of the laser due to the interference of the outgoing and cantilever-reflected waves. Due to the multiple reflections resulting in the interference, the light absorption by the probe cantilever is greatly enhanced compared with a single pass case. Interaction of infrared emission of a diode laser with different probes has been studied.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Microscopic conductivity of lattice fermions at equilibrium. I. Non-interacting particles

We consider free lattice fermions subjected to a static bounded potential and a time- and space-dependent electric field. For any bounded convex region ℛ ⊂ ℝ{sup d} (d ≥ 1) of space, electric fields E within R drive currents. At leading order, uniformly with respect to the volume |R| of R and the particular choice of the static potential, the dependency on E of the current is linear and described by a conductivity (tempered, operator-valued) distribution. Because of the positivity of the heat production, the real part of its Fourier transform is a positive measure, named here (microscopic) conductivity measure of R, in accordance with Ohm’s law in Fourier space. This finite measure is the Fourier transform of a time-correlation function of current fluctuations, i.e., the conductivity distribution satisfies Green–Kubo relations. We additionally show that this measure can also be seen as the boundary value of the Laplace–Fourier transform of a so-called quantum current viscosity. The real and imaginary parts of conductivity distributions are related to each other via the Hilbert transform, i.e., they satisfy Kramers–Kronig relations. At leading order, uniformly with respect to parameters, the heat production is the classical work performed by electric fields on the system in presence of currents. The conductivity measure is uniformly bounded with respect to parameters of the system and it is never the trivial measure 0 dν. Therefore, electric fields generally produce heat in such systems. In fact, the conductivity measure defines a quadratic form in the space of Schwartz functions, the Legendre–Fenchel transform of which describes the resistivity of the system. This leads to Joule’s law, i.e., the heat produced by currents is proportional to the resistivity and the square of currents.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗