Analyzing capacitance-voltage measurements of vertical wrapped-gated nanowires

The capacitance of arrays of vertical wrapped-gate InAs nanowires are analyzed. With the help of a Poisson-Schr"odinger solver, information about the doping density can be obtained directly. Further features in the measured capacitance-voltage characteristics can be attributed to the presence of surface states as well as the coexistence of electrons and holes in the wire. For both scenarios, quantitative estimates are provided. It is furthermore shown that the difference between the actual capacitance and the geometrical limit is quite large, and depends strongly on the nanowire material.Comment: 15 pages, 6 Figures included, to appear in Nanotechnolog

Application of the Controllable Unit Approach (CUA) to analyzing safeguards measurement systems

CUA is a material control and accountability methodology that takes into account the system logic and statistical characteristics of a plant process through the formulation of closure equations. The study evaluated CUA methodology to meet performance oriented regulations. The criterion is defined as the detection of a material loss of two kilograms of SNM with 97.5% confidence. Specifically investigated were the timeliness of detection, the ability to localize material loss, process coverage, cost/benefits, and compatibility with other safeguards techniques such as diversion path analysis and data filtering. The feasibility of performance-oriented regulations is demonstrated. To fully use the system of closure equations, a procedure was developed to formally integrate the effect of both short-term and long-term closure equations into an overall systems criterion of performance. Both single and multiple diversion strategies are examined in order to show how the CUA method can protect against either strategy. Quantitative results show that combined closure equations improve the detection sensitivity to material loss, and that multiple diversions provide only diminishing returns

The MoS2 Nanotubes with Defect-Controlled Electric Properties

We describe a two-step synthesis of pure multiwall MoS2 nanotubes with a high degree of homogeneity in size. The Mo6S4I6 nanowires grown directly from elements under temperature gradient conditions in hedgehog-like assemblies were used as precursor material. Transformation in argon-H2S/H2 mixture leads to the MoS2 nanotubes still grouped in hedgehog-like morphology. The described method enables a large-scale production of MoS2 nanotubes and their size control. X-ray diffraction, optical absorption and Raman spectroscopy, scanning electron microscopy with wave dispersive analysis, and transmission electron microscopy were used to characterize the starting Mo6S4I6 nanowires and the MoS2 nanotubes. The unit cell parameters of the Mo6S4I6 phase are proposed. Blue shift in optical absorbance and metallic behavior of MoS2 nanotubes in two-probe measurement are explained by a high defect concentration

Mineralogical and geochemical analysis of Fe-phases in drill-cores from the Triassic Stuttgart Formation at Ketzin CO₂ storage site before CO₂ arrival

Reactive iron (Fe) oxides and sheet silicate-bound Fe in reservoir rocks may affect the subsurface storage of CO2 through several processes by changing the capacity to buffer the acidification by CO2 and the permeability of the reservoir rock: (1) the reduction of three-valent Fe in anoxic environments can lead to an increase in pH, (2) under sulphidic conditions, Fe may drive sulphur cycling and lead to the formation of pyrite, and (3) the leaching of Fe from sheet silicates may affect silicate diagenesis. In order to evaluate the importance of Fe-reduction on the CO2 reservoir, we analysed the Fe geochemistry in drill-cores from the Triassic Stuttgart Formation (Schilfsandstein) recovered from the monitoring well at the CO2 test injection site near Ketzin, Germany. The reservoir rock is a porous, poorly to moderately cohesive fluvial sandstone containing up to 2–4 wt% reactive Fe. Based on a sequential extraction, most Fe falls into the dithionite-extractable Fe-fraction and Fe bound to sheet silicates, whereby some Fe in the dithionite-extractable Fe-fraction may have been leached from illite and smectite. Illite and smectite were detected in core samples by X-ray diffraction and confirmed as the main Fe-containing mineral phases by X-ray absorption spectroscopy. Chlorite is also present, but likely does not contribute much to the high amount of Fe in the silicate-bound fraction. The organic carbon content of the reservoir rock is extremely low (<0.3 wt%), thus likely limiting microbial Fe-reduction or sulphate reduction despite relatively high concentrations of reactive Fe-mineral phases in the reservoir rock and sulphate in the reservoir fluid. Both processes could, however, be fuelled by organic matter that is mobilized by the flow of supercritical CO2 or introduced with the drilling fluid. Over long time periods, a potential way of liberating additional reactive Fe could occur through weathering of silicates due to acidification by CO2

Statistical problems arising from simulation of a high-throughput nuclear facility

Shortages in traditional energy sources, such as oil and natural gas, have placed greater emphasis on alternative fuel sources. With an already developed technological base and cost history, nuclear power is an attractive option. However, the public's attitude toward recent terrorism has generated strong demands for improved safeguards measures to deter, detect, and protect against diversion of special nuclear material (SNM). To encourage improved safeguards accountability, the Nuclear Regulatory Commission (NRC) has been considering the use of performance oriented regulations to supplement those currently used. A study, sponsored by NRC/Office of Standards Development, was conducted to evaluate the controllable unit approach (CUA) to meeting performance oriented regulations. The study results are used to provide the NRC with a methodology that systematically and iteratively compares the actual situation to the need before additions or refinements are imposed. And because the existing or proposed system is mathematically modeled, modifications to the process for any reason can be tested quickly for their effect on material control before implementation. A summary flow diagram of the CUA methodology is shown and described

Resolution enhancement of transmission electron microscopy by super-resolution radial fluctuations

Super-resolution fluorescence microscopy techniques have enabled dramatic development in modern biology due to their capability to discern features smaller than the diffraction limit of light. Recently, super-resolution radial fluctuations (SRRF), an analytical approach that is capable of generating super-resolution images easily without the need for specialized hardware or photoswitchable fluorophores, has been presented. While SRRF has only been demonstrated on fluorescence microscopes, in principle, this method can be used to generate super-resolution images on any imaging platforms with intrinsic radial symmetric point spread functions. In this work, we show that SRRF can be utilized to enhance the resolution and quality of transmission electron microscopy (TEM) images. By including an image registration algorithm to correct for sample drift, the SRRF-TEM approach substantially enhances the resolution of TEM images of three different samples acquired with a commercial TEM system. We quantify the resolution improvement in SRRF-TEM and evaluate how SRRF parameters affect the resolution and quality of SRRF-TEM results

Projected performance of experimental InAs/GaAsSb/GaSb TFET as millimeter-wave detector

Based on measurements of a vertical nanowire InAs/GaAsSb/GaSb tunneling field-effect transistor (TFET) that exhibited minimum subthreshold swing of 48 mV/dec and a record high I60 of 0.31 μA/μm, a SPICE model has been generated to allow an experimentally-based prediction of the nanowire TFET technology. At 30 GHz the detector has been simulated to reveal a sensitivity of 4.8 kV/W biased near zero volts (VGS =-0.06 V, VDS = 0.1 V). A maximum sensitivity of over 4000 kV/W has been obtained under biased conditions. These results exceed prior measurements of an In0.53Ga0.47As/GaAs0.5Sb0.5 heterojunction TFET by over an order of magnitude

Hybrid phase-change — Tunnel FET (PC-TFET) switch with subthreshold swing < 10mV/decade and sub-0.1 body factor: Digital and analog benchmarking

In this paper we report the first hybrid Phase-Change - Tunnel FET (PC-TFET) device configurations for achieving a deep sub-thermionic steep subthreshold swing at room temperature and subthreshold power savings. The proposed hybrid device feedbacks the steep transition of Metal-Insulator transition in a VO2 structure into Gate or Source configurations of strained silicon nanowire Tunnel FETs, to achieve a switching with lon/Ioff better that 5.5×106 and with a subthreshold swing of 4.0 mV/dec at 25 °C. We demonstrate that the principle of PC-TFET switching relates to an internal amplification resulting in a sub-unity body factor, m, which is reduced to values below 0.1 for a current range larger than 2-3 decades. We report a full experimental digital and analog benchmarking of the new device and compare it with Tunnel FETs and CMOS. Remarkably, the PC-TFET can achieve analog figures of merit like gm/Id breaking the 40 V-1 limit of MOSFETs. We demonstrate and report the first buffered oscillator cell for neuromorphic computing exploiting the gate configuration of PC-TFET