Synthesis of Atomically Thin Hexagonal Diamond with Compression
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99 GENERAL AND MISCELLANEOUS↗
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Quantitative Electromechanical Atomic Force Microscopy
The ability to probe a materials electromechanical functionality on the nanoscale is significant to applications from energy storage and computing to biology and medicine. Voltage modulated atomic force microscopy (VM-AFM) has become a mainstay characterization tool for investigating these materials due to its ability to locally probe electromechanically responsive materials with spatial resolution from microns to nanometers. However, with the wide popularity of VM-AFM techniques such as piezoresponse force microscopy (PFM) and electrochemical strain microscopy (ESM) there has been a rise in reports of nanoscale electromechanical functionality, including hysteresis, in materials that should be incapable of exhibiting piezo- or ferroelectricity. Explanations for the origins of unexpected nanoscale phenomena have included new material properties, surface-mediated polarization changes and/or spatially resolved behavior that is not present in bulk measurements. At the same time, it is well known that VM-AFM measurements are vulnerable to numerous forms of crosstalk and, despite efforts within the AFM community, a global approach for eliminating this has remained elusive. Here, we develop a method for easily demonstrating the presence of hysteretic ( i.e. “false ferroelectric”) long-range interactions between the sample and cantilever body. This approach should be easy to implement in any VM-AFM measurement. We then go on to demonstrate fully quantitative and repeatable nanoelectromechanical characterization using an interferometer. These quantitative measurements are critical for a wide range of devices including mems actuators and sensors, memristor, energy storage and memory.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Graphene diamond-like carbon films heterostructure
A limitation to the potential use of graphene as an electronic material is the lack of control over the 2D materials properties once it is deposited on a supporting substrate. Here, the use of Diamond-like Carbon (DLC) interlayers between the substrate and the graphene is shown to offer the prospect of overcoming this problem. The DLC films used here, more properly known as a-C:H with ∼25% hydrogen content, have been terminated with N or F moieties prior to graphene deposition. It is found that nitrogen terminations lead to an optical band gap shrinkage in the DLC, whilst fluorine groups reduce the DLC's surface energy. CVD monolayer graphene subsequently transferred to DLC, N terminated DLC, and F terminated DLC has then been studied with AFM, Raman and XPS analysis, and correlated with Hall effect measurements that give an insight into the heterostructures electrical properties. The results show that different terminations strongly affect the electronic properties of the graphene heterostructures. G-F-DLC samples were p-type and displayed considerably higher mobility than the other heterostructures, whilst G-N-DLC samples supported higher carrier densities, being almost metallic in character. Since it would be possible to locally pattern the distribution of these differing surface terminations, this work offers the prospect for 2D lateral control of the electronic properties of graphene layers for device applications.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
A bolometer based on single-walled carbon nanotubes and hybrid materials
We have designed a bolometric IR detector based on freestanding aerosol synthesised carbon nanotubes and hybrid graphene materials deposited on a film suspended over a hole in the substrate. In this case, graphene serves as an absorber. The effect of the amount of the deposited absorber on the spectral characteristics, voltage sensitivity, response time and noise of the bolometer is investigated. The best response time is observed for the samples of pristine carbon nanotubes, whereas the hybrid sample with the largest amount of graphene demonstrates the highest sensitivity to radiation. Moreover, we have measured and analysed the bolometer parameters as functions of the ambient pressure and temperature, which has allowed us to determine the optimum operating conditions for the device. (paper)
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Hard X-ray Fluorescence Measurements of Heteroepitaxial Solid Oxide Fuel Cell Cathode Materials
Commonly, SOFCs are operated at high temperatures (above 800°C). At these temperatures expensive housing is needed to contain an operating stack as well as coatings to contain the oxidation of the metallic interconnects. Lowering the temperature of an operating device would allow for more conventional materials to be used, thus lowering overall cost. Understanding the surface chemical states of cations in the surface of the SOFC cathode is vital to designing a system that will perform well at lower temperatures. The samples studied were grown by pulsed laser deposition (PLD) at the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory (PNNL). 20% strontium doped lanthanum manganite (LSM-20) was grown on YSZ and NGO (neodymium gallate). The films on YSZ have a fiber texture. LSM-20 on NGO is heteroepitaxial. Lanthanum strontium cobalt ferrite (LSCF-6428) films were grown on LAO and YSZ with a GDC barrier layer. Total X-ray Reflection Fluorescence (TXRF) was used to depth profile the samples. In a typical experiment, the angle of the incident beam is varied though the critical angle. Below the critical angle, the x-ray decays as an evanescent wave and will only penetrate the top few nanometers. TXRF experiments done on LSM films have suggested strontium segregates to the surface and form strontium enriched nanoparticles (1). It should be pointed out that past studies have focused on 30% strontium A-site doping, but this project uses 20% strontium doped lanthanum manganite. XANES and EXAFS data were taken as a function of incoming angle to probe composition as a function of depth. XANES spectra can be difficult to analyze fully. For other materials density functional theory calculations compared to near edge measurements have been a good way to understand the 3d valence electrons (2).
Environmental Molecular Sciences Laboratory↗
2010-2012 California Household Travel Survey
The 2010-2012 California Household Travel Survey (CHTS) was administered by the California Department of Transportation, which collected demographic and travel behavior characteristics for residents across the entire state. At the time, it was the largest such regional or statewide survey ever conducted in the United States. Detailed travel behavior information was obtained from more than 42,500 households via multiple data-collection methods, including computer-assisted telephone interviewing, online and mail surveys, wearable (7,574 participants) and in-vehicle (2,910 vehicles) global positioning system devices, and on-board diagnostic sensors that gathered data directly from a vehicle's engine. Details of personal travel behavior were gathered within the region of residence, inter-regionally within the state, and in adjoining states and Mexico. The survey sampling plan was designed to ensure an accurate representation of the entire population of the state. The CHTS included additional features, such as vehicle-acquisition decisions, parking choices, work schedules and flexibility, use of toll lanes/priced facilities, and walk and bicycle trips, to support advanced model development.
1Hz data↗
Level 2 Exceedance Response Action (ERA) Technical Report
For Drainage 13 Demonstration: Two storm water treatment (bioretention) devices have been installed downstream of the scrap yard at Livermore. The bioretention basins are sized to contain the 85th percentile storm. It is expected that this bioretention basins will lower the Fe and Al concentrations below the NALs. In addition, the sampling location ST-13-1 will be moved to the combined overflow of the bioretention basins. Since the basins are sized to retain the 85th percentile storm, it is expected that samples will only be able to be collected during large storms. For Drainage 20 Demonstration: All corrodible metal stored outside of the machine shops at buildings 906 and 907 have been removed.
54 ENVIRONMENTAL SCIENCES↗
HPC Molecular Simulation Tries Out a New GPU: Experiences on Early AMD Test Systems for the Frontier Supercomputer
Molecular simulation is an important tool for nu- merous efforts in physics, chemistry, and the biological sciences. Simulating molecular dynamics requires extremely rapid cal- culations to enable sufficient sampling of simulated temporal molecular processes. The Hewlett Packard Enterprise (HPE) Cray EX Frontier supercomputer installed at the Oak Ridge Leadership Computing Facility (OLCF) will provide an exascale resource for open science, and will feature graphics processing units (GPUs) from Advanced Micro Devices (AMD). The future LUMI supercomputer in Finland will be based on an HPE Cray EX platform as well. Here we test the ports of several widely used molecular dynamics packages that have each made substantial use of acceleration with NVIDIA GPUs, on Spock, the early Cray pre-Frontier testbed system at the OLCF which employs AMD GPUs. These programs are used extensively in industry for pharmaceutical and materials research, as well as academia, and are also frequently deployed on high-performance computing (HPC) systems, including national leadership HPC resources. We find that in general, performance is competitive and installation is straightforward, even at these early stages in a new GPU ecosystem. Our experiences point to an expanding arena for GPU vendors in HPC for molecular simulation.
Sedova, Ada↗
Post-Closure Environmental Sampling and Inspection at the Amchitka Island, Alaska, Site - 17251
In the 1960's and early 1970's, three underground nuclear tests were conducted on Amchitka Island, Alaska. In 1965, the US Department of Defense-in conjunction with the US Atomic Energy Commission (AEC)-conducted the first of these nuclear tests, Long Shot, to provide data that would improve US capabilities for detecting underground nuclear explosions. In 1969, AEC conducted the second test, Milrow, to explore the feasibility of detonating a much larger device. In 1971, AEC conducted the third test, Cannikin, which was the largest underground test ever conducted by the US. The Long-Term Surveillance Plan (LTSP) for the Amchitka, Alaska, Site details how the US Department of Energy Office of Legacy Management (LM) intends to fulfill its mission to protect human health and the environment at and around the Amchitka Island site. The LTSP calls for monitoring to be performed every 5 years, at least during the initial phase of the project. The purpose of the monitoring is to develop a baseline of activity concentrations for selected radionuclides in biota, water, and soil, both on Amchitka Island and at the reference location on Adak Island, approximately 322 kilometers (200 miles) northeast of Amchitka. In addition to the environmental monitoring activities, seven mud pit caps that contain diesel-contaminated soils are inspected. The plan for biological and water sampling (both seawater and freshwater) during the May 2016 sampling event was developed through close coordination with the primary stakeholders, including the Alaska Department of Environmental Conservation, the Aleutian Pribilof Islands Association, and the US Fish and Wildlife Service. The environmental sampling in 2016 is a continuation of LM's evaluation of Amchitka Island's environment. Previous results from similar monitoring programs in 2004 and 2011 indicate that the environment is not being impacted by radionuclide migration and uptake from the underground nuclear testing conducted beneath Amchitka Island; consequently, subsistence and commercial-catch seafood is safe for human consumption. The collection of biota samples (rockfish, Irish lords, greenling, and rockweed) for cesium-134 ({sup 134}Cs), cesium-137 ({sup 137}Cs), plutonium-239 ({sup 239}Pu), plutonium-240 ({sup 240}Pu), and freshwater and seawater samples for {sup 134}Cs, {sup 137}Cs, and tritium ({sup 3}H) was the primary objective of the 2016 sampling effort. Rockfish, Irish lords, and greenling are resident, nonmigratory fish species that spend their entire life cycle in the marine environment, and rockweed is an inter-tidal species that may concentrate cesium. The seawater samples were collected primarily to determine if leakage from the Long Shot detonation could be detected and, secondarily, to compare with the background seawater samples collected from Adak Island. Cesium isotopes are also being analyzed to better understand the potential impact that the Fukushima-Daiichi release might have on the Amchitka and Adak environments. The target detection limits used for the 2016 sampling are lower than those used in previous studies. The lower detection limits make it possible for LM to delineate background activity levels for the radionuclides of interest. Data from the 2016 sampling event go beyond assessing food safety and focus on detecting leakage from the underground nuclear explosions. Additionally, the baseline activity concentrations obtained for the reference area (Adak Island) will enable identification of quantitative statistical trends in the results of future sampling programs. Sampling programs conducted in 2021 and beyond will have an objective to assess the statistical trends of radioactivity levels in the Amchitka Island environment. (authors)
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
Geometrically Tunable Beamed Light Emission from a Quantum‐Dot Ensemble Near a Gradient Metasurface
Abstract Optical metasurfaces have been widely investigated in recent years as a means to tailor the wavefronts of externally incident light for passive device applications. At the same time, their use in active optoelectronic devices such as light emitters is far less established. This work explores their ability to control the radiation properties of a nearby continuous ensemble of randomly oriented incoherent dipole sources via near‐field interactions. Specifically, a film of colloidal quantum dots is deposited on a plasmonic metasurface consisting of a 1D array of metallic nanoantennas on a metal film. The array is designed to introduce a linear phase profile upon reflection, and a bi‐periodic nanoparticle arrangement is introduced to ensure adequate sampling of the desired phase gradient. Highly directional radiation patterns are correspondingly obtained from the quantum dots at an enhanced emission rate. The underlying radiation mechanism involves the near‐field excitation of surface plasmon polaritons at the metal film, and their selective diffractive scattering by the metasurface into well‐collimated beams along predetermined geometrically tunable directions. These results underscore the distinctive ability of metasurfaces to control radiation properties directly at the source level, which is technologically significant for the continued miniaturization and large‐scale integration of optoelectronic devices.
Wang, Xiaowei↗
Partnership for Edge Physics (EPSI), University of Texas Final Report
Simulations of tokamak plasmas require a number of inputs whose values are uncertain. The effects of these input uncertainties on the reliability of model predictions is of great importance when validating predictions by comparison to experimental observations, and when using the predictions for design and operation of devices. However, high fidelity simulation of tokamak plasmas, particular those aimed at characterization of the edge plasma physics, are computationally expensive, so lower cost surrogates are required to enable practical uncertainty estimates. Two surrogate modeling techniques have been explored in the context of tokamak plasma simulations using the XGC family of plasma simulation codes. The first is a response surface surrogate, and the second is an augmented surrogate relying on scenario extrapolation. In addition, to reduce the costs of the XGC simulations, a particle resampling algorithm was developed, which allows marker particle distributions to be adjusted to maintain optimal importance sampling. This means that the total number of particles in and therefore the cost of a simulation can be reduced while maintaining the same accuracy.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Probing unintentional Fe impurity incorporation in MOCVD homoepitaxy GaN: Toward GaN vertical power devices
Unintentional impurity incorporation in GaN drift layers represents a challenging issue that can limit their potential performance in vertical power devices. In this paper, we focus on studying the origins of Fe impurity incorporation in metal-organic chemical vapor deposition (MOCVD) grown GaN materials. Acting as a compensator in n-type GaN drift layers, Fe impurities can reduce the electron mobility in GaN and limit the lowest controllable doping level. Two sources, the sample cleaning process and growth susceptor, were identified as the main mechanisms of Fe incorporation in the MOCVD GaN growth process. It was found that solvent cleaning of the wafer can introduce significant Fe contamination at the growth interface, which would slowly be incorporated into the GaN epilayer, thus causing background Fe impurity as high as 10 17 cm -3 level. Moreover, the Fe impurity in the coating material on the susceptor can introduce additional Fe impurity during the growth process. Our studies revealed that the Fe impurity level could be significantly suppressed by more than two orders when an alternative cleaning process was used and the susceptor surface was fully covered by substrates. Characterization of the Fe impurity concentrations was performed via secondary ion mass spectrometry. The trap level (E C - 0.57) eV from deep-level transient spectroscopy that had previously been attributed to Fe confirmed the carrier compensation effect from Fe. Room temperature Hall mobility as high as 1007 cm 2 /V s was achieved on the MOCVD grown low-Fe GaN. Results from this work will provide guidance for achieving high purity GaN toward high performance GaN vertical power devices.
42 ENGINEERING↗
Multipurpose epithermal neutron beam on new research station at MARIA research reactor in Swierk-Poland
MARIA reactor is an open-pool research reactor what gives the chance to install uranium fission converter on the periphery of the core. It could be installed far enough not to induce reactivity of the core but close enough to produce high flux of fast neutrons. Special design of the converter is now under construction. It is planned to set the research stand based on such uranium converter in the near future: in 2015 MARIA reactor infrastructure should be ready (preparation started in 2013), in 2016 the neutron beam starts and in 2017 opening the stand for material and biological research or for medical training concerning BNCT. Unused for many years, horizontal channel number H2 at MARIA research rector in Poland, is going to be prepared as a part of unique stand. The characteristics of the neutron beam will be significant advantage of the facility. High flux of neutrons at the level of 2x10{sup 9} cm{sup -2}s{sup -1} will be obtainable by uranium neutron converter located 90 cm far from the reactor core fuel elements (still inside reactor core basket between so called core reflectors). Due to reaction of core neutrons with converter U{sub 3}Si{sub 2} material it will produce high flux of fast neutrons. After conversion neutrons will be collimated and moderated in the channel by special set of filters and moderators. At the end of H2 channel i.e. at the entrance to the research room neutron energy will be in the epithermal energy range with neutron intensity at least at the level required for BNCT (2x10{sup 9} cm{sup -2}s{sup -1}). For other purposes density of the neutron flux could be smaller. The possibility to change type and amount of installed filters/moderators which enables getting different properties of the beam (neutron energy spectrum, neutron-gamma ratio and beam profile and shape) is taken into account. H2 channel is located in separate room which is adjacent to two other empty rooms under the preparation for research laboratories (200 m2). It is planned to create fully equipped complex facility possible to perform various experiments on the intensive neutron beam. Epithermal neutron beam enables development across the full spectrum of materials research for example shielding concrete tests or electronic devices construction improvement. Due to recent reports on the construction of the accelerator for the Boron Neutron Capture Therapy (BNCT) it has the opportunity to become useful and successful method in the fight against brain and other types of cancers not treated with well known medical methods. In Europe there is no such epithermal neutron source which could be used throughout the year for training and research for scientist working on BNCT what makes the stand unique in Europe. Also our research group which specializes in mixed radiation dosimetry around nuclear and medical facilities would be able to carry out research on new detectors and methods of measurements for radiological protection and in-beam (therapeutic) dosimetry. Another group of scientists from National Centre for Nuclear Research, where MARIA research reactor is located, is involved in research of gamma detector systems. There is an idea to develop Prompt-gamma Single Photon Emission Computed Tomography (Pg- SPECT). This method could be used as imaging system for compounds emitting gamma rays after nuclear reaction with thermal neutrons e.g. for boron concentration in BNCT. Inside the room, where H2 channel is located, there is another horizontal channel - H1 which is also unused. Simultaneously with the construction of the H2 stand it will be possible to create special pneumatic horizontal mail inside the H1 channel for irradiation material samples in the vicinity of the core i.e. in the distal part of the H1 channel. It might expand the scope of research at the planned neutron station. Secondly it is planned to equip both stands with moveable positioning system, video system and facilities to perform animal experiments (anaesthesia, vital signs control, imaging devices, positioning). These all above make constructed station unique in the world (uranium fission converter-based beam) and the only one of such intense neutron beam in the Europe. Moreover implementation of the station would allow the development of research on a number of issues for researchers from all over the Europe. One of very important advantages of the station is undisturbed exploitation of the reactor and other vertical and horizontal channels. MARIA reactor operates 6000 hours per year and that amount of time will be achievable for research on the neutron station. It have to be underlined that new neutron station will work parallel to all another ventures. (authors)
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
Enabling Real-Time Volume Rendering of Functional Magnetic Resonance Imaging on an iOS Device
Powerful non-invasive imaging technologies like computed tomography (CT), ultrasound, and magnetic resonance imaging (MRI) are used daily by medical professionals to diagnose and treat patients. While 2D slice viewers have long been the standard, many tools allowing 3D representations of digital medical data are now available. The newest imaging advancement, functional MRI (fMRI) technology, has changed medical imaging from viewing static to dynamic physiology (4D) over time, particularly to study brain activity. Add this to the rapid adoption of mobile devices for everyday work and the need to visualize fMRI data on tablets or smartphones arises. However, there are few mobile tools available to visualize 3D MRI data, let alone 4D fMRI data. Building volume rendering tools on mobile devices to visualize 3D and 4D medical data is challenging given the limited computational power of the devices. This paper describes research that explored the feasibility of performing real-time 3D and 4D volume raycasting on a tablet device. The prototype application was tested on a 9.7” iPad Pro using two different fMRI datasets of brain activity. The results show that mobile raycasting is able to achieve between 20 and 40 frames per second for traditional 3D datasets, depending on the sampling interval, and up to 9 frames per second for 4D data. While the prototype application did not always achieve true real-time interaction, these results clearly demonstrated that visualizing 3D and 4D digital medical data is feasible with a properly constructed software framework.
62 RADIOLOGY AND NUCLEAR MEDICINE↗
Focused Ion Beam Preparation of Low Melting Point Metals: Lessons Learned From Indium
Indium (In) and other low melting point metals are used as interconnects in a variety of hybridized circuits and a full understanding of the metallurgy of these interconnects is important to the reliability and performance of the devices. Here, this paper shows that room temperature focused ion beam (FIB) preparation of cross-sections, using Ga + or Xe + can result in artifacts that obscure the true In microbump structure. The use of modified milling strategies to minimize the increased local sample temperature are shown to produce cross-sections that are representative of the In bump microstructure in some sample configurations. Furthermore, cooling of the sample to cryogenic temperatures is shown to reliably eliminate artifacts in FIB prepared cross-sections of In bumps allowing the true bump microstructure to be observed.
36 MATERIALS SCIENCE↗
Bismuth in Lead–Tin Alloy Perovskites: Effect on Material Properties and Photovoltaic Device Performance
Metal halide perovskites (MHPs) have a strong potential for optoelectronic applications, especially photovoltaics. A significant advantage offered by MHPs is their bandgap tunability via chemical substitution and alloying, with lead–tin alloys producing the narrowest reported bandgaps of ~1.2 eV. Efforts to further narrow the bandgap of MHPs by alloying in other elements, such as bismuth, have largely been unsuccessful due to the introduction of defective electronic states, which severely diminish electronic quality. Here, in this study, we examine the effects of bismuth on a lead–tin alloyed MHP, motivated by the narrow bandgap of alloyed lead–tin MHPs. We find that the defect screening observed in lead–tin MHPs is not sufficient to screen the defect level introduced by bismuth, as evidenced by quenched photoluminescence, decreased mobility, and severely reduced performance in a photovoltaic device. Density functional theory calculations suggest that midgap states are introduced by bismuth addition over a range of chemical and compositional conditions. We further observe through wavelength-dependent photoconductivity that free carriers are generated out to ~0.9 eV in bismuth-containing samples, which could be of potential interest for NIR photodetection.
14 SOLAR ENERGY↗
Spatio-Kinetic Electronic Heterogeneity in MoS 2 Revealed by Ultrafast Electron Microscopy: Implications for Optoelectronics
There is broad interest in layered, two-dimensional (2D) semiconductors owing to their high optical absorption and ability to heterogeneously integrate with various substrates. In such layered semiconductors, mesoscopic imperfections, such as surface step edges, may affect charge carrier kinetics and device performance, but studying their effects on carrier transport with sufficient spatial and temporal resolution is a challenge. Using scanning ultrafast electron microscopy, we image the near-surface charge carrier kinetics with μm/ps spatiotemporal resolution in single-crystal MoS 2 samples with surface steps tens of nanometers in height. We find an approximately 3-fold increase in surface trap density near such surface steps compared to the uniform, flat surface regions. Despite the difference in trap state density, filling of the traps occurs over the same time scale (∼100 ps), but carrier recovery is much slower near the step compared to the uniform regions of the material. Furthermore, these results provide an approach to measure ultrafast dynamics and determine the required uniformity of layered materials depending on the speed limit constraints for specific applications.
SEM↗
High transition temperature superconductor/insulator bilayers for the development of ultra-fast electronics
High transition temperature superconductor (HTc)/SrTiO{sub 3} (STO) bilayers were fabricated by sputtering deposition on (100) STO substrates. Their transport and morphological properties were characterized using conductive atomic force microscopy. The STO barriers present good insulating properties, with long attenuation lengths (λ ∼ 1 nm) which reduce the junction resistance and increase the operating critical current. The samples present roughness values smaller than 1 nm, with an extremely low density of surface defects (∼5 × 10{sup −5} defects/μm{sup 2}). The high control of the barrier quality over large defect free surfaces is encouraging for the development of microelectronics devices based in HTc Josephson junctions.
36 MATERIALS SCIENCE↗