159 research outputs found
A Pearson Effective Potential for Monte-Carlo simulation of quantum confinement effects in various MOSFET architectures
A Pearson Effective Potential model for including quantization effects in the
simulation of nanoscale nMOSFETs has been developed. This model, based on a
realistic description of the function representing the non zero-size of the
electron wave packet, has been used in a Monte-Carlo simulator for bulk, single
gate SOI and double-gate SOI devices. In the case of SOI capacitors, the
electron density has been computed for a large range of effective field
(between 0.1 MV/cm and 1 MV/cm) and for various silicon film thicknesses
(between 5 nm and 20 nm). A good agreement with the Schroedinger-Poisson
results is obtained both on the total inversion charge and on the electron
density profiles. The ability of an Effective Potential approach to accurately
reproduce electrostatic quantum confinement effects is clearly demonstrated.Comment: 13 pages, 11 figures, 3 table
Dopant-controlled single-electron pumping through a metallic island
We investigate a hybrid metallic island / single dopant electron pump based
on fully-depleted silicon on insulator technology. Electron transfer between
the central metallic island and the leads is controlled by resonant tunneling
through single phosphorus dopants in the barriers. Top gates above the barriers
are used control the resonance conditions. Applying radio frequency signals to
the gates, non-adiabatic quantized electron pumping is achieved. A simple
deterministic model is presented and confirmed by comparing measurements with
simulations
A silicon-based single-electron interferometer coupled to a fermionic sea
We study Landau-Zener-Stueckelberg-Majorana (LZSM) interferometry under the
influence of projective readout using a charge qubit tunnel-coupled to a
fermionic sea. This allows us to characterise the coherent charge qubit
dynamics in the strong-driving regime. The device is realised within a silicon
complementary metal-oxide-semiconductor (CMOS) transistor. We first read out
the charge state of the system in a continuous non-demolition manner by
measuring the dispersive response of a high-frequency electrical resonator
coupled to the quantum system via the gate. By performing multiple fast
passages around the qubit avoided crossing, we observe a multi-passage LZSM
interferometry pattern. At larger driving amplitudes, a projective measurement
to an even-parity charge state is realised, showing a strong enhancement of the
dispersive readout signal. At even larger driving amplitudes, two projective
measurements are realised within the coherent evolution resulting in the
disappearance of the interference pattern. Our results demonstrate a way to
increase the state readout signal of coherent quantum systems and replicate
single-electron analogues of optical interferometry within a CMOS transistor
Effects of two common fungicides on the reproduction of Aporrectodea caliginosa in natural soil
The use of pesticides in agroecosystems can have negative effects on earthworms, which play key roles in soil functioning such as organic matter decomposition. The aim of this study was to assess the effects of two fungicides (Cuprafor micro®, composed of copper oxychloride, and Swing Gold®, composed of epoxiconazole (EPX) and dimoxystrobin (DMX)) on earthworm reproduction by exposing adults and cocoons. First, adult Aporrectodea caliginosa individuals were exposed for 28 days to 3.33, 10 and 30 times the recommended dose (RD) of Cuprafor micro® corresponding to 25.8, 77.5 and 232.5 mg kg−1 dry soil of copper, respectively, and 0.33, 1 and 3 times the RD of Swing Gold® (corresponding to 5.2 × 10−2 mg DMX kg−1 + 1.94 × 10−2 mg EPX kg−1, 1.55 × 10−1 mg DMX kg−1 + 5.81 × 10−2 mg EPX kg−1 and 4.62 × 10−1 mg DMX kg−1 + 1.74 × 10−1 mg EPX kg−1 respectively), in addition to a control soil with no fungicide treatment. Cocoon variables (production, weight, hatching success, hatching time) were monitored. Second, “naïve” cocoons produced by uncontaminated earthworms were exposed to soils contaminated by the same concentrations of the two fungicides, and we assessed hatching success and hatching time. In the first experiment, cocoon production was halved at the highest copper concentration (232.5 mg Cu kg−1 of dry soil) as compared to the control. Cocoons took 5 more days to hatch, and the hatching success decreased by 35% as compared to the control. In the Swing Gold® treatments, cocoon production was reduced by 63% at 3 times the RD, and the hatching success significantly decreased by 16% at the RD. In the second experiment, only the hatching success of cocoons was impacted by Swing Gold® at 3 times the RD (30% less hatching). It is concluded that the cocoon stock in the soil is crucial for the renewal of populations in the field. The most sensitive endpoint was the hatching success of the cocoons produced by exposed adults. This endpoint and the effects observed on the “naïve” cocoons could be taken into account in pesticide risk assessment
Contact resistances in trigate and FinFET devices in a Non-Equilibrium Green's Functions approach
We compute the contact resistances in trigate and FinFET devices
with widths and heights in the 4 to 24 nm range using a Non-Equilibrium Green's
Functions approach. Electron-phonon, surface roughness and Coulomb scattering
are taken into account. We show that represents a significant part
of the total resistance of devices with sub-30 nm gate lengths. The analysis of
the quasi-Fermi level profile reveals that the spacers between the heavily
doped source/drain and the gate are major contributors to the contact
resistance. The conductance is indeed limited by the poor electrostatic control
over the carrier density under the spacers. We then disentangle the ballistic
and diffusive components of , and analyze the impact of different
design parameters (cross section and doping profile in the contacts) on the
electrical performances of the devices. The contact resistance and variability
rapidly increase when the cross sectional area of the channel goes below
nm. We also highlight the role of the charges trapped at the
interface between silicon and the spacer material.Comment: 16 pages, 15 figure
Electric-field tuning of the valley splitting in silicon corner dots
We perform an excited state spectroscopy analysis of a silicon corner dot in
a nanowire field-effect transistor to assess the electric field tunability of
the valley splitting. First, we demonstrate a back-gate-controlled transition
between a single quantum dot and a double quantum dot in parallel that allows
tuning the device in to corner dot formation. We find a linear dependence of
the valley splitting on back-gate voltage, from to with a slope of (or equivalently a slope
of with respect to the effective field). The
experimental results are backed up by tight-binding simulations that include
the effect of surface roughness, remote charges in the gate stack and discrete
dopants in the channel. Our results demonstrate a way to electrically tune the
valley splitting in silicon-on-insulator-based quantum dots, a requirement to
achieve all-electrical manipulation of silicon spin qubits.Comment: 5 pages, 3 figures. In this version: Discussion of model expanded;
Fig. 3 updated; Refs. added (15, 22, 32, 34, 35, 36, 37
A Pearson Effective Potential for Monte-Carlo Simulation of Quantum Confinement Effects in nMOSFETs
Pauli Blockade in a Few-Hole PMOS Double Quantum Dot limited by Spin-Orbit Interaction
We report on hole compact double quantum dots fabricated using conventional
CMOS technology. We provide evidence of Pauli spin blockade in the few hole
regime which is relevant to spin qubit implementations.
A current dip is observed around zero magnetic field, in agreement with the
expected behavior for the case of strong spin-orbit. We deduce an intradot spin
relaxation rate 120\,kHz for the first holes, an important step
towards a robust hole spin-orbit qubit
Earthworms mitigate pesticide effects on soil microbial activities
Earthworms act synergistically with microorganisms in soils. They are ecosystem engineers involved in soil organic matter degradation and nutrient cycling, leading to the modulation of resource availability for all soil organisms. Using a soil microcosm approach, we aimed to assess the influence of the earthworm Aporrectodea caliginosa on the response of soil microbial activities against two fungicides, i.e. Cuprafor micro® (copper oxychloride, a metal) and Swing® Gold (epoxiconazole and dimoxystrobin, synthetic organic compounds). The potential nitrification activity (PNA) and soil enzyme activities (glucosidase, phosphatase, arylamidase, and urease) involved in biogeochemical cycling were measured at the end of the incubation period, together with earthworm biomass. Two common indices of the soil biochemistry were used to aggregate the response of the soil microbial functioning: the geometric mean (Gmean) and the Soil Quality Index (SQI). At the end of the experiment, the earthworm biomass was not impacted by the fungicide treatments. Overall, in the earthworm-free soil microcosms, the two fungicides significantly increased several soil enzyme and nitrification activities, leading to a higher GMean Index as compared to the non-treated control soils. The microbial activity responses depended on the type of activity (nitrification was the most sensitive one), on the fungicide (Swing® Gold or Cuprafor micro®), and on the doses. The SQI indices revealed higher effects of both fungicides on the soil microbial activity in the absence of earthworms. The presence of earthworms enhanced all soil microbial activities in both the control and fungicide-contaminated soils. Moreover, the magnitude of the fungicide impact, integrated through the SQI index, was mitigated by the presence of earthworms, conferring a higher stability of microbial functional diversity. Our results highlight the importance of biotic interactions in the response of indicators of soil functioning (i.e., microbial activity) to pesticides
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