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Exploring Graphene Field Effect Transistor Devices to Improve Spectral Resolution of Semiconductor Radiation Detectors

Howell, Stephen W.; Martin, Jeffrey B.

Graphene, a planar, atomically thin form of carbon, has unique electrical and material properties that could enable new high performance semiconductor devices. Graphene could be of specific interest in the development of room-temperature, high-resolution semiconductor radiation spectrometers. Incorporating graphene into a field-effect transistor architecture could provide an extremely high sensitivity readout mechanism for sensing charge carriers in a semiconductor detector, thus enabling the fabrication of a sensitive radiation sensor. In addition, the field effect transistor architecture allows us to sense only a single charge carrier type, such as electrons. This is an advantage for room-temperature semiconductor radiation detectors, which often suffer from significant hole trapping. Here we report on initial efforts towards device fabrication and proof-of-concept testing. This work investigates the use of graphene transferred onto silicon and silicon carbide, and the response of these fabricated graphene field effect transistor devices to stimuli such as light and alpha radiation.

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TYPE SAND Report YEAR 2013
DOIOSTI

Sustainability innovation foundry - FY13: Merging research and operations

Mcneish, Jerry; Mizner, Jack H.; Passell, Howard; Keller, Elizabeth; Sullivan, Kristina; Gordon, Margaret

Sustainability is a critical national security issue for the U.S. and other nations. Sandia National Laboratories (SNL) is already a global leader in sustainability science and technology (SS&T) as documented in this report. This report documents the ongoing work conducted this year as part of the Sustainability Innovation Foundry (SIF). The efforts of the SIF support Sandia's national and international security missions related to sustainability and resilience revolving around energy use, water use, and materials, both on site at Sandia and externally. The SIF leverages existing Sandia research and development (R&D) in sustainability science and technology to support new solutions to complex problems. The SIF also builds on existing Sandia initiatives to support transformation of Sandia into a fully sustainable entity in terms of materials, energy, and water use. In the long term, the SIF will demonstrate the efficacy of sustainability technology developed at Sandia through prototyping and test bed approaches and will provide a common platform for support of solutions to the complex problems surrounding sustainability. Highlights from this year include the Sustainability Idea Challenge, improvements in facilities energy use, lectures and presentations from relevant experts in sustainability [Dr. Barry Hughes, University of Denver], and significant development of the Institutional Transformation (IX) modeling tools to support evaluation of proposed modifications to the SNL infrastructure to realize energy savings.

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TYPE SAND Report YEAR 2013
DOIOSTI

LDRD final report : mesoscale modeling of dynamic loading of heterogeneous materials

Robbins, Joshua; Dingreville, Remi; Voth, Thomas E.; Furnish, Michael D.

Material response to dynamic loading is often dominated by microstructure (grain structure, porosity, inclusions, defects). An example critically important to Sandia's mission is dynamic strength of polycrystalline metals where heterogeneities lead to localization of deformation and loss of shear strength. Microstructural effects are of broad importance to the scientific community and several institutions within DoD and DOE; however, current models rely on inaccurate assumptions about mechanisms at the sub-continuum or mesoscale. Consequently, there is a critical need for accurate and robust methods for modeling heterogeneous material response at this lower length scale. This report summarizes work performed as part of an LDRD effort (FY11 to FY13; project number 151364) to meet these needs.

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TYPE SAND Report YEAR 2013
DOIOSTI

Edge Remap for Solids

Love, Edward; Robinson, Allen C.; Ridzal, Denis

We review the edge element formulation for describing the kinematics of hyperelastic solids. This approach is used to frame the problem of remapping the inverse deformation gradient for Arbitrary Lagrangian-Eulerian (ALE) simulations of solid dynamics. For hyperelastic materials, the stress state is completely determined by the deformation gradient, so remapping this quantity effectively updates the stress state of the material. A method, inspired by the constrained transport remap in electromagnetics, is reviewed, according to which the zero-curl constraint on the inverse deformation gradient is implicitly satisfied. Open issues related to the accuracy of this approach are identified. An optimization-based approach is implemented to enforce positivity of the determinant of the deformation gradient. The efficacy of this approach is illustrated with numerical examples.

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TYPE SAND Report YEAR 2013
DOIOSTI

Theoretical and experimental studies of electrified interfaces relevant to energy storage

Hayden, Carl C.; Templeton, J.A.; Jones, Reese E.; Kliewer, Christopher; Sasaki, Darryl Y.; Reyes, Karla R.

Advances in technology for electrochemical energy storage require increased understanding of electrolyte/electrode interfaces, including the electric double layer structure, and processes involved in charging of the interface, and the incorporation of this understanding into quantitative models. Simplified models such as Helmholtz's electric double-layer (EDL) concept don't account for the molecular nature of ion distributions, solvents, and electrode surfaces and therefore cannot be used in predictive, high-fidelity simulations for device design. This report presents theoretical results from models that explicitly include the molecular nature of the electrical double layer and predict critical electrochemical quantities such as interfacial capacitance. It also describes development of experimental tools for probing molecular properties of electrochemical interfaces through optical spectroscopy. These optical experimental methods are designed to test our new theoretical models that provide descriptions of the electric double layer in unprecedented detail.

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TYPE SAND Report YEAR 2013
DOIOSTI

Uncertainty and sensitivity analysis for photovoltaic system modeling

Pohl, Andrew

We report an uncertainty and sensitivity analysis for modeling DC energy from photovoltaic systems. We consider two systems, each comprised of a single module using either crystalline silicon or CdTe cells, and located either at Albuquerque, NM, or Golden, CO. Output from a PV system is predicted by a sequence of models. Uncertainty in the output of each model is quantified by empirical distributions of each model's residuals. We sample these distributions to propagate uncertainty through the sequence of models to obtain an empirical distribution for each PV system's output. We considered models that: (1) translate measured global horizontal, direct and global diffuse irradiance to plane-of-array irradiance; (2) estimate effective irradiance from plane-of-array irradiance; (3) predict cell temperature; and (4) estimate DC voltage, current and power. We found that the uncertainty in PV system output to be relatively small, on the order of 1% for daily energy. Four alternative models were considered for the POA irradiance modeling step; we did not find the choice of one of these models to be of great significance. However, we observed that the POA irradiance model introduced a bias of upwards of 5% of daily energy which translates directly to a systematic difference in predicted energy. Sensitivity analyses relate uncertainty in the PV system output to uncertainty arising from each model. We found that the residuals arising from the POA irradiance and the effective irradiance models to be the dominant contributors to residuals for daily energy, for either technology or location considered. This analysis indicates that efforts to reduce the uncertainty in PV system output should focus on improvements to the POA and effective irradiance models.

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TYPE SAND Report YEAR 2013
DOIOSTI

Compressive sensing for nuclear security

Gestner, Brian J.

Special nuclear material (SNM) detection has applications in nuclear material control, treaty verification, and national security. The neutron and gamma-ray radiation signature of SNMs can be indirectly observed in scintillator materials, which fluoresce when exposed to this radiation. A photomultiplier tube (PMT) coupled to the scintillator material is often used to convert this weak fluorescence to an electrical output signal. The fluorescence produced by a neutron interaction event differs from that of a gamma-ray interaction event, leading to a slightly different pulse in the PMT output signal. The ability to distinguish between these pulse types, i.e., pulse shape discrimination (PSD), has enabled applications such as neutron spectroscopy, neutron scatter cameras, and dual-mode neutron/gamma-ray imagers. In this research, we explore the use of compressive sensing to guide the development of novel mixed-signal hardware for PMT output signal acquisition. Effectively, we explore smart digitizers that extract sufficient information for PSD while requiring a considerably lower sample rate than conventional digitizers. Given that we determine the feasibility of realizing these designs in custom low-power analog integrated circuits, this research enables the incorporation of SNM detection into wireless sensor networks.

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TYPE SAND Report YEAR 2013
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Results 55001–55100 of 99,299
Results 55001–55100 of 99,299