hole density
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Author(s):  
Jing Li ◽  
Yong Zhou ◽  
Yanjie Wang ◽  
Sen Zhou ◽  
Ruijie Zhang ◽  
...  

Abstract Black phosphorus (BP) is a two-dimensional and layered elemental semiconductor that is very sensitive to the subtle fluctuation of relative humidity (RH). However, the practical application of BP material was undesirably plagued by the irreversible degradation under moisture/oxygen atmospheres. To circumvent this limitation, here we prepared BP co-doped with benzyl viologen (BV) and Au nanoparticles as the sensing layer and explored the humidity-sensing performance at room temperature (20 oC). Unlike BP (BP-BV) counterparts, BP-Au (BP-BV-Au) sensors demonstrated unvaried response polarity with increasing RH. And BV introduction improved the recovery characteristics. Additionally, the ternary BP-BV-Au sensors delivered decent selectivity and negligible hysteresis. On the one hand, the in situ reduction of Au nanoparticles consumed lone electron pairs within BP, suppressed the interaction with ambient moisture/oxygen, and improved the operation stability and recovery. On the other hand, hydrophobic BV as the protection layer further hindered water attachment. This co-doping behavior reduced the hole density and ensured the predominant interaction between low-energy sorption sites within BP and water molecules, thus leading to a larger resistance modulation (i.e., stronger response) and quicker reaction kinetics. This work offered a feasible method to propel the practical application and enriched the sensing mechanisms of BP-based humidity sensors.


2022 ◽  
Vol 3 (1) ◽  
pp. 15-26
Author(s):  
Argyris Tilemachou ◽  
Matthew Zervos ◽  
Andreas Othonos ◽  
Theodoros Pavloudis ◽  
Joseph Kioseoglou

Cu3N with a cubic crystal structure is obtained in this paper by the sputtering of Cu under N2 followed by annealing under NH3: H2 at 400 °C, after which it was doped with iodine at room temperature resulting into p-type Cu3N with hole densities between 1016 and 1017 cm−3. The Cu3N exhibited distinct maxima in differential transmission at ~2.01 eV and 1.87 eV as shown by ultrafast pump-probe spectroscopy, corresponding to the M and R direct energy band gaps in excellent agreement with density functional theory calculations, suggesting that the band gap is clean and free of mid-gap states. The Cu3N was gradually converted into optically transparent γ-CuI that had a hole density of 4 × 1017 cm−3, mobility of 12 cm2/Vs and room temperature photoluminescence at 3.1 eV corresponding to its direct energy band gap. We describe the fabrication and properties of γ-CuI/TiO2/Cu3N and γ-CuI/Cu3N p-n heterojunctions that exhibited rectifying current-voltage characteristics, but no photogenerated current attributed to indirect recombination via shallow states in Cu3N and/or deep states in the γ-CuI consistent with the short (ps) lifetimes of the photoexcited electrons-holes determined from transient absorption–transmission spectroscopy.


Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7890
Author(s):  
Friedhard Römer ◽  
Martin Guttmann ◽  
Tim Wernicke ◽  
Michael Kneissl ◽  
Bernd Witzigmann

In the past years, light-emitting diodes (LED) made of GaN and its related ternary compounds with indium and aluminium have become an enabling technology in all areas of lighting. Visible LEDs have yet matured, but research on deep ultraviolet (UV) LEDs is still in progress. The polarisation in the anisotropic wurtzite lattice and the low free hole density in p-doped III-nitride compounds with high aluminium content make the design for high efficiency a critical step. The growth kinetics of the rather thin active quantum wells in III-nitride LEDs makes them prone to inhomogeneous broadening (IHB). Physical modelling of the active region of III-nitride LEDs supports the optimisation by revealing the opaque active region physics. In this work, we analyse the impact of the IHB on the luminescence and carrier transport III-nitride LEDs with multi-quantum well (MQW) active regions by numerical simulations comparing them to experimental results. The IHB is modelled with a statistical model that enables efficient and deterministic simulations. We analyse how the lumped electronic characteristics including the quantum efficiency and the diode ideality factor are related to the IHB and discuss how they can be used in the optimisation process.


2021 ◽  
Author(s):  
Guo Wei-Gui ◽  
Pei Zi-Xi ◽  
Qiu Xiang-Gang

Abstract Superconducting films with the same hole density but different geometric symmetry have been designed and fabricated. The R(H) curves show obvious periodic oscillations with several dips at fractional matching fields. It is found that the period of the oscillations in the low field is not necessary equal to that derived from the hole density, but consistent with that from the corresponding wire networks when the large disk-like film regions are regarded as nodes. The experimental results of R(H), T c (H) and j c (H) at fractional matching fields within the first oscillation also support the rationality of considering films with large-diametered hole arrays as wire networks. Our results demonstrate that the connectivity of superconducting films with large-diametered hole arrays plays a more important role in the oscillations of R(H) curves.


2021 ◽  
Author(s):  
Yernur Akashev ◽  
Samira Ahmad ◽  
Chiara Cavalleri ◽  
Yulia Ignatochkina ◽  
Yevgenii Solodkiy

Abstract Field A is located in the center of the Dnieper-Donets basin (DDB), producing gas from clastic reservoirs from several deep horizons in the Upper Visean sediments. The case study highlights the application of advanced pulsed neutron logging technologies and high-resolution data processing to unlock the sedimentary layers’ characteristics and the gas potential behind the casing. Multiple rock measurements are simultaneously recorded for continuous lithology identification, porosity quantification, and differentiating gas-filled porosity from low porosity formations. Dedicated log data acquisition and processing techniques enable investigating the effect of thin laminations on reservoir quality and producibility. The use of advanced pulsed neutron logging and interpretation method reduces the operational risks while securing critical reservoir parameters. A pulsed neutron spectroscopy tool provided a rich dataset including a self-compensated sigma and neutron porosity logs, fast neutron cross section (FNXS) together with capture and inelastic elemental spectroscopy. The logs interpretation was performed integrating FNXS and very high-resolution neutron porosity with mineral dry weight fractions and matrix properties from elemental spectroscopy processing. The comparison between the pulsed neutron measurements with standard open hole logs highlights the critical role of advanced fit-to-purpose logging techniques to accurately describe the underlying complexity of the formation and obtain improved net reservoir and net pay thicknesses in laminated and heterogeneous sequences. The logging objectives were successfully met, and additional valuable information related to the reservoir were determined in an efficient manner. The study also shows the critical value of FNXS as confident gas measurement. The FNXS measures the ability of the formation interacting with fast neutrons which are highly dependent on atomic density and not dominated by particular isotopes such as traditional sigma and porosity measurements. It is highly sensitive to gas-filled porosity, but it is independent of hydrogen index, acting like a cased-hole density measurement. Moreover, it demonstrates the importance of accurate knowledge of the mineralogy and matrix as well as the ability to measure at very high resolution to unravel the highly layered nature of the formation and its implication on completion and production strategy. Pulsed neutron logging has evolved over a half century, but the intrinsic physical measurements remain unchanged. With the advent and introduction of the new FNXS measurement and a high-quality spectroscopy elemental concentration, a higher quality measurement and interpretation can be obtained from standalone pulsed neutron logging. The advanced technology and log data analysis interpretation module can be considered as an effective and comprehensive methodology for robust formation evaluation in similar and complex setting.


2021 ◽  
Vol 13 (22) ◽  
pp. 4709
Author(s):  
Haiyang Shi ◽  
Qun Pan ◽  
Geping Luo ◽  
Olaf Hellwich ◽  
Chunbo Chen ◽  
...  

Understanding the impacts of environmental factors on spatial–temporal and large-scale rodent distribution is important for rodent damage prevention. Investigating rat hole density (RHD) is one of the most effective methods to obtain the intensity of rodent damage. However, most of the previous field surveys or UAV-based remote sensing methods can only evaluate small-scale RHD and its influencing factors. However, these studies did not consider large-scale temporal and spatial heterogeneity. Therefore, we collected small-scale and in situ measurement records of RHD on the northern slope of the Tien Shan Mountains in Xinjiang (NTXJ), China, from 1982 to 2015, and then used correlation analysis and Bayesian network (BN) to analyze the environmental impacts on large-scale RHD with satellite remote sensing data such as the GIMMS NDVI product. The results show that the built BN can better quantify causality in the environmental mechanism modeling of RHD. The NDVI and LAI data from satellite remote sensing are important to the spatial–temporal RHD distribution and the mapping in the future. In regions with an elevation higher than 600 m (UPR) and lower than 600 m (LWR) of NTXJ, there are significant differences in the driving mechanism patterns of RHD, which are dependent on the elevation variation. In LWR, vegetation conditions have a weaker impact on RHD than UPR. It is possibly due to the Artemisia eaten by the dominant species Lagurus luteus (LL) in UPR being more sensitive to precipitation and temperature if compared with the Haloxylon ammodendron eaten by the Rhombomys opimus (RO) in LWR. In LWR, grazing intensity is more strongly and positively correlated to RHD than UPR, possibly due to both winter grazing and RO dependency on vegetation distribution; moreover, in UPR, sheep do not feed Artemisia as the main food, and the total vegetation is sufficient for sheep and LL to coexist. Under the different conditions of water availability of LWR and UPR, grazing may affect the ratio of aboveground and underground biomass by photosynthate allocation, thereby affecting the distribution of RHD. In extremely dry years, the RHD of LWR and UPR may have an indirect interactive relation due to changes in grazing systems.


2021 ◽  
Vol 63 (11) ◽  
pp. 988-993
Author(s):  
Cagatay Elibol ◽  
Horst Paul Strunk

Abstract There is a trend towards smaller and smaller structures (nanostructures/ miniaturization) which is well-known in microelectronic, energy and semiconductor applications. Nanoengineering is expected to lead to significant improvements in the intrinsic properties of structures, e. g., in energy storage for supercapacitors. In this context, a deeper understanding of the growth mechanisms of the thinnest crystal layers is of crucial importance for the controlled growing of nanowhiskers with outstanding properties. In the present study, we consider a simple whisker growth model based on the surface energy (i. e., wettability) of the components and investigate the effect of the carbon interlayer deposited on a Si (111) wafer using the magnetron sputtering technique on the whisker formation during the subsequent molecular beam epitaxy process in the Si-C-Cu system. In the present study, the topographic holes in the carbon layer which are the preferred nucleation areas of whiskers were identified by a series of scanning tunneling microscopy analyses, and the natural hole density was statistically determined. Using atomic force microscopy, the surface roughness of the carbon layer was characterized. The results of our investigations indicate that there is a correlation between the hole density in the carbon layer and the density of Cu nanowhiskers. This may validate the supposition that the holes in the carbon layer are the preferred nucleation sites for whiskers – an effect that could be relevant for future works on the growth of nanowhiskers at predefined positions.


2021 ◽  
Vol 11 (1) ◽  
pp. 173-181
Author(s):  
Dadan Hamdani ◽  
Soni Prayogi ◽  
Yoyok Cahyono ◽  
Gatut Yudoyono ◽  
Darminto Darminto

In this work, the imbalances in band gap energy between p-window layer and intrinsic layer (p/i interface) in p-i-n type solar cells to suppress charge recombination adopting with the addition of buffer layer, at p/i interface, namely solar cell structures without buffer (Cell A) and with buffer (Cell B). Using well-practiced AFORS-HET software, performances of Cell A and Cell B structures are evaluated and compared to experimental data. A good agreement between AFORS-HET modelling and experimental data was obtained for Cell A (error = 1.02%) and Cell B (error = 0.07%), respectively. The effects of dopant concentrations of the p-type and n-type were examined with respect to cell B for better performance by analysing the energy band diagram, the electric field distribution, the trapped hole density, the light J-V characteristics, and the external quantum efficiency. The simulated results of an optimised Cell B showed that the highest efficiency of 8.81% (VOC = 1042 mV, JSC = 10.08 mA/cm2, FF = 83.85%) has been obtained for the optimum dopant values of NA = 1.0 x 1019 cm-3 and ND = 1.0 x 1019 cm-3, respectively. A comparison between experimental data and simulation results for Cell B showed that the conversion efficiency can be enhanced from 5.61% to 8.81%, using the optimized values


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shuqiu Wang ◽  
Peayush Choubey ◽  
Yi Xue Chong ◽  
Weijiong Chen ◽  
Wangping Ren ◽  
...  

AbstractAn unidentified quantum fluid designated the pseudogap (PG) phase is produced by electron-density depletion in the CuO2 antiferromagnetic insulator. Current theories suggest that the PG phase may be a pair density wave (PDW) state characterized by a spatially modulating density of electron pairs. Such a state should exhibit a periodically modulating energy gap $${\Delta }_{{{{{{\rm{P}}}}}}}({{{{{\boldsymbol{r}}}}}})$$ Δ P ( r ) in real-space, and a characteristic quasiparticle scattering interference (QPI) signature $${\Lambda }_{{{{{{\rm{P}}}}}}}({{{{{\boldsymbol{q}}}}}})$$ Λ P ( q ) in wavevector space. By studying strongly underdoped Bi2Sr2CaDyCu2O8 at hole-density ~0.08 in the superconductive phase, we detect the 8a0-periodic $${\Delta }_{{{{{{\rm{P}}}}}}}({{{{{\boldsymbol{r}}}}}})$$ Δ P ( r ) modulations signifying a PDW coexisting with superconductivity. Then, by visualizing the temperature dependence of this electronic structure from the superconducting into the pseudogap phase, we find the evolution of the scattering interference signature $$\Lambda ({{{{{\boldsymbol{q}}}}}})$$ Λ ( q ) that is predicted specifically for the temperature dependence of an 8a0-periodic PDW. These observations are consistent with theory for the transition from a PDW state coexisting with d-wave superconductivity to a pure PDW state in the Bi2Sr2CaDyCu2O8 pseudogap phase.


2021 ◽  
Vol 2021 (9) ◽  
Author(s):  
Jordan Cotler ◽  
Kristan Jensen

Abstract It has long been known that the coarse-grained approximation to the black hole density of states can be computed using classical Euclidean gravity. In this work we argue for another entry in the dictionary between Euclidean gravity and black hole physics, namely that Euclidean wormholes describe a coarse-grained approximation to the energy level statistics of black hole microstates. To do so we use the method of constrained instantons to obtain an integral representation of wormhole amplitudes in Einstein gravity and in full-fledged AdS/CFT. These amplitudes are non-perturbative corrections to the two-boundary problem in AdS quantum gravity. The full amplitude is likely UV sensitive, dominated by small wormholes, but we show it admits an integral transformation with a macroscopic, weakly curved saddle-point approximation. The saddle is the “double cone” geometry of Saad, Shenker, and Stanford, with fixed moduli. In the boundary description this saddle appears to dominate a smeared version of the connected two-point function of the black hole density of states, and suggests level repulsion in the microstate spectrum. Using these methods we further study Euclidean wormholes in pure Einstein gravity and in IIB supergravity on Euclidean AdS5× S5. We address the perturbative stability of these backgrounds and study brane nucleation instabilities in 10d supergravity. In particular, brane nucleation instabilities of the Euclidean wormholes are lifted by the analytic continuation required to obtain the Lorentzian spectral form factor from gravity. Our results indicate a factorization paradox in AdS/CFT.


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