A study was conducted to compare the δ(O2/N2) scales used by four laboratories engaged in atmospheric δ(O2/N2) measurements. These laboratories are the Research Institute for Environmental Management ...Technology, Advanced Industrial Science and Technology (EMRI/AIST); the National Institute for Environmental Studies (NIES); Tohoku University (TU); and Scripps Institution of Oceanography (SIO). Therefore, five high-precision standard mixtures for theO2 molar fraction gravimetrically prepared by the National Metrology Institute of Japan, AIST (NMIJ/AIST) with a standard uncertainty of less than 5 per meg (0.001 ‰) were used as round-robin standard mixtures. EMRI/AIST, NIES, TU, and SIO reported the analyzed values of the standard mixtures on their own δ(O2/N2) scales, and the values were compared with the δ(O2/N2) values gravimetrically determined by NMIJ/AIST (the NMIJ/AIST scale). The δ(O2/N2) temporal drift in the five standard mixtures during the intercomparison experiment from May 2017 to March 2020 was corrected based on the δ(O2/N2) values analyzed before and after the laboratory measurements by EMRI/AIST. The scales are compared based on offsets in zero and span. The relative span offsets of EMRI/AIST, TU, NIES, and SIO scales against the NMIJ/AIST scale were -0.11%±0.10%, -0.10%±0.13%,3.39%±0.13%, and 0.93%±0.10%, respectively. The largest offset corresponded to a 0.30 Pgyr-1 decrease and increase in global estimates for land biospheric and oceanic CO2 uptakes based on trends in atmospheric CO2 and δ(O2/N2). The deviations in the measured δ(O2/N2) values on the laboratory scales from the NMIJ/AIST scale are 65.8±2.2, 425.7±3.1, 404.5±3.0, and 596.4±2.4 per meg for EMRI/AIST, TU, NIES, and SIO, respectively. The difference between atmospheric δ(O2/N2) values observed at Hateruma Island (HAT; 24.05∘ N, 123.81∘ E), Japan, by EMRI/AIST and NIES were reduced from -329.3±6.9 to -6.6±6.8 per meg by converting their scales to the NMIJ/AIST scale.
A discharge-based proton transfer reaction (PTR) ion source was operated using a mixture of H2O and rare gases such as He, Ne, Ar, and Kr in combination with a custom-built time-of-flight (TOF) mass ...spectrometer. In contrast to an “H2O-only” discharge, which usually functions above a field strength (E/N) of 100 Td for a drift tube, an “H2O-rare gas”-based discharge was operated successfully at E/N values between 30 and 50 Td. (E is the electric field strength (V cm-1), N is the buffer gas number density (molecule cm-3), and 1 Td=10-17 cm2 V molecule-1.) The intensity of primary ions (H3O+·(H2O)n) generated in the “H2O-rare gas” discharge was comparable to that in the “H2O-only” discharge. Although detection sensitivities decreased for nonpolar molecules such as isoprene, benzene, toluene, and p-xylene, they increased for polar molecules such as acetone and acetaldehyde. This suggests that the operation of the PTR-TOF mass spectrometer at low drift-tube field-strengths improves both the detection sensitivity and selectivity for the polar molecules. In addition, fragmentation in the drift tube was suppressed significantly for fragile species such as methyl nitrate, in the low E/N operation.
The exponential development in quantum phenomena is directly correlated with the decreasing size of nano‐semiconductor transistors. Consequently, the use of a quantum structure that deviates from ...traditional transistor types becomes imperative. Electrostatically defined nanoscale devices within 2D semiconductor heterostructures serve as foundational elements for diverse quantum electrical circuits. Van der Waals heterostructures, distinguished by atomically flat interfaces and inherent 2D characteristics, offer advantages such as large‐scale uniformity, flexibility, and portability over conventional bulk semiconductor heterostructures. Herein, the intricate electronic behavior of a MoS2/WSe2 encapsulated heterostructure governed by split‐gate and middle‐gate configurations is investigated, revealing a distinctive step‐like current profile at a low temperature of 77 K. The observed four regimes in the current highlight the impact of quantum confinement induced by reduced lateral dimensions, coupled with precise electrostatic confinement controlled by gate voltages. The temperature dependence of the phenomena emphasizes the role of thermal effects on carrier scattering mechanisms. In addition, the pinch‐off characteristics with different temperatures, middle‐gate voltages, and drain biases are explored. This study contributes to a deeper understanding of electrostatic effects in 2D transition metal dichalcogenide heterostructures and holds promise for the development of advanced electronic devices with tailored confinement for enhanced functionalities.
Electrostatically defined nanoscale devices within 2D semiconductor heterostructures, especially van der Waals heterostructures, offer advantages such as uniformity and flexibility. Investigating MoS2/WSe2 heterostructures under split gate and middle gate control unveils unique electronic behavior, highlighting quantum confinement and precise electrostatic control, and advancing the understanding of 2D materials for future electronic devices.
Abstract The exponential development in quantum phenomena is directly correlated with the decreasing size of nano‐semiconductor transistors. Consequently, the use of a quantum structure that deviates ...from traditional transistor types becomes imperative. Electrostatically defined nanoscale devices within 2D semiconductor heterostructures serve as foundational elements for diverse quantum electrical circuits. Van der Waals heterostructures, distinguished by atomically flat interfaces and inherent 2D characteristics, offer advantages such as large‐scale uniformity, flexibility, and portability over conventional bulk semiconductor heterostructures. Herein, the intricate electronic behavior of a MoS 2 /WSe 2 encapsulated heterostructure governed by split‐gate and middle‐gate configurations is investigated, revealing a distinctive step‐like current profile at a low temperature of 77 K. The observed four regimes in the current highlight the impact of quantum confinement induced by reduced lateral dimensions, coupled with precise electrostatic confinement controlled by gate voltages. The temperature dependence of the phenomena emphasizes the role of thermal effects on carrier scattering mechanisms. In addition, the pinch‐off characteristics with different temperatures, middle‐gate voltages, and drain biases are explored. This study contributes to a deeper understanding of electrostatic effects in 2D transition metal dichalcogenide heterostructures and holds promise for the development of advanced electronic devices with tailored confinement for enhanced functionalities.
Monolayer materials are strongly affected by their potential fluctuations, which can be induced by an intrinsic corrugation or the surface roughness of the substrate. We compare the effective ...exciton-exciton annihilation (EEA) rate constants of monolayer WS2 on substrates with different surface topographies. We show that the WS2 monolayers on the substrates with atomically flat terraces have small effective EEA rate constants that deviate from the overall tendency and exhibit multiple exciton decay components, which cannot be accounted for by the conventional EEA model. To obtain a correct description, it is important to use a quantized EEA model. The intrinsic EEA rate constants for the flat-terrace substrates determined by this model are comparable to that of hBN-encapsulated monolayer WS2.
Abstract
The inverse problem of estimating the background potential from measurements of the local density of states is a challenging issue in quantum mechanics. Even more difficult is to do this ...estimation using approximate methods such as scanning gate microscopy (SGM). Here, we propose a machine-learning-based solution by exploiting adaptive cellular neural networks (CNNs). In the paradigmatic setting of a quantum point contact, the training data consist of potential-SGM functional relations represented by image pairs. These are generated by the recursive Green’s function method. We demonstrate that the CNN-based machine learning framework can predict the background potential corresponding to the experimental image data. This is confirmed by analyzing the estimated potential with image processing techniques based on the comparison between the charge densities and those obtained using different techniques. Correlation analysis of the images suggests the possibility of estimating different contributions to the background potential. In particular, our results indicate that both charge puddles and fixed impurities contribute to the spatial patterns found in the SGM data. Our work represents a timely contribution to the rapidly evolving field of exploiting machine learning to solve difficult problems in physics.
Precise monitoring of changes in atmospheric O2 levels was
implemented by preparing primary standard mixtures with less than
1 µmol mol−1 standard uncertainty for O2 molar fractions. In this
study, ...these mixtures were crafted in 10 L high-pressure aluminium alloy
cylinders using a gravimetric method in which unknown uncertainty factors
were theoretically determined and subsequently reduced. Molar fractions of
the constituents (CO2, Ar, O2, and N2) in the primary
standard mixtures were mainly resolved using masses of the respective source
gases (CO2, Ar, O2, and N2) that had been filled into the
cylinders. To precisely determine the masses of the source gases, the
difference in mass of the cylinder before and after filling the respective
source gas was calculated by comparison with an almost identical reference
cylinder. Although the masses of the cylinders filled with the source gas with
respect to the reference cylinder tended to deviate in relation to
temperature differences between the source-gas-filled cylinder and
surrounding air, the degree of the deviation could be efficiently reduced by
measuring the two cylinders at the exact same temperature. The standard
uncertainty for the cylinder mass obtained in our weighing system was
determined to be 0.82 mg. The standard uncertainties for the O2 molar
fractions in the primary standard mixtures ranged from 0.7
to 0.8 µmol mol−1. Based on the primary standard
mixtures, the annual average molar fractions of atmospheric O2 and Ar
in 2015 at Hateruma island, Japan, were found to be 209339.1±1.1
and 9334.4±0.7 µmol mol−1,
respectively. The molar fraction for atmospheric Ar was in agreement with
previous reports.
PDF
