Bias Conditions Research Articles

In-plane mixed-dimensional 2D/2D/1D MoS2/MoTe2/Mo6Te6 heterostructures for low contact resistance optoelectronics

Mixed-dimensional heterostructures formed by combining 2D materials and other dimensional (0D, 1D, and 3D) materials provide new opportunities for various applications owing to their novel properties. However, in-plane mixed-dimensional heterostructures have been rarely investigated. Here, we report a novel flux-controlled chemical vapor deposition method for synthesizing in-plane mixed-dimensional heterostructures composed of monolayer MoS2 and low-dimensional Mo/Te compounds. By adjusting the Te flux and growth time, we controlled the composition, dimension, and phase of the Mo/Te compounds interfaced with the MoS2. While in-plane 2D/1D MoS2/Mo6Te6 and 2D/2D/1D MoS2/2H MoTe2/Mo6Te6 heterostructures were obtained with a low Te flux, in-plane 2D/2D MoS2/mixed 2H-1T’ MoTe2 and 2D/2D MoS2/2H MoTe2 heterostructures were synthesized with a high Te flux. We investigated the transport properties of the devices fabricated with in-plane mixed-dimensional 2D/2D/1D MoS2/2H MoTe2/Mo6Te6 heterostructures and imaged localized electronic band structures using scanning photocurrent microscopy. Under the low bias condition, the device exhibited an Ohmic-like behavior, which has not been achieved in conventional devices with stacked van der Waals junctions. Under the high bias condition, the device showed a rectifying behavior because of band-bending formed at the heterojunctions; this is consistent with the electronic band-alignment expected from the bandgap and electron affinity of the materials.

(Digital Presentation) Analysis of MIS-HEMT Kink Effect in Saturation Region

In this work, the Metal-Insulator-Semiconductor High Electron Mobility Transistor (MIS-HEMT) behavior in saturation region was analyzed and compared with a GaN MOSFET. The MIS-HEMT presents a current level about 30 times higher than GaN MOSFET, for the same bias conditions. The different saturation points (VDS sat) of the MOS and HEMT conductions is responsible for the appearance of a kink in the drain current (IDS) current as a function of drain voltage (VDS) curve. The output conductance (gD) of the MOSFET presented a strong dependence on VGT, while the MIS-HEMT only a slightly dependence was observed. The MIS-HEMT kink effect (MH kink) was defined by the drain voltage where the bump occurs. The MH kink only occurs for a high enough gate bias to enable the MOS conduction, and MH kink value increases with the gate voltage overdrive (VGT) and its variation tends to saturate for VGT higher than 3,5V.

The impact of affective states and traits on perceptual stability during binocular rivalry

Affective states and traits have been associated with different measures of perceptual stability during binocular rivalry. Diverging approaches to measuring perceptual stability as well as to examination of the role of affective variables have contributed to an inconclusive pattern of findings. Here, we studied the influence of affective traits, such as depressiveness and trait anxiety, and states, which were manipulated with a musical mood induction paradigm, on different measures of perceptual stability (dominance ratios and phase durations) during binocular rivalry. Fifty healthy participants reported alternations in two conditions: a biased perception condition with an unequal probability of perceiving stimuli, using an upright versus a tilted face with a neutral expression, and a control condition with equal chances of perceiving stimuli, using Gabors of different orientations. Baseline positive state affect significantly predicted longer phase durations whereas affective traits did not yield any such effect. Furthermore, in an exploratory analysis, induced negative affect attenuated stimulus related bias in predominance ratios. Overall, we found a strong correlation between both measures of perceptual stability (phase durations and dominance ratios). Our findings thus question the distinction between different measures of perceptual stability during binocular rivalry and highlight the role of affective states in its formation.

Multi-Electron Transfer at H-Terminated p-Si Electrolyte Interfaces: Large Photovoltages under Inversion Conditions.

Photovoltages for hydrogen-terminated p-Si(111) in an acetonitrile electrolyte were quantified with methyl viologen [1,1'-(CH3)2-4,4'-bipyridinium](PF6)2, abbreviated MV2+, and [Ru(bpy)3](PF6)2, where bpy is 2,2'-bipyridine, that respectively undergo two and three one-electron transfer reductions. The reduction potentials, E°, of the two MV2+ reductions occurred at energies within the forbidden bandgap, while the three [Ru(bpy)3]2+ reductions occurred within the continuum of conduction band states. Bandgap illumination resulted in reduction that was more positive than that measured with a degenerately doped n+-Si demonstrative of a photovoltage, Vph, that increased in the order MV2+/+ (260 mV) < MV+/0 (400 mV) < Ru2+/+ (530 mV) ∼ Ru+/0 (540 mV) ∼ Ru0/- (550 mV). Pulsed 532 nm excitation generated electron-hole pairs whose dynamics were nearly constant under depletion conditions and increased markedly as the potential was raised or lowered. A long wavelength absorption feature assigned to conduction band electrons provided additional evidence for the presence of an inversion layer. Collectively, the data reveal that the most optimal photovoltage, as well as the longest electron-hole pair lifetime and the highest surface electron concentration, occurs when E° lies energetically within the unfilled conduction band states where an inversion layer is present. The bell-shaped dependence for electron-hole pair recombination with the surface potential was predicted by the time-honored SRH model, providing a clear indication that this interface provides access to all four bias conditions, i.e., accumulation, flat band, depletion, and inversion. The implications of these findings for photocatalysis applications and solar energy conversion are discussed.

Wear and Corrosion Performance of Ti-6Al-4V Alloy Arc-Coated TiN/CrN Nano-Multilayer Film

The objective of this study was to investigate the effect of varying bias parameters (−50 V, −100 V, and −150 V) on the properties of TiN/CrN multilayer films deposited on Ti-6Al-4V alloy using the cathodic arc deposition (CAD) technique. The deposited films were characterized for their composition, structure, morphology, thickness, adhesion, and hardness. Wear and polarization tests were also conducted to determine the optimal bias condition for wear and corrosion resistance. The results showed that the TiN/CrN films possessed a nano-multilayered structure comprising TiN and CrN phases. The hard coating significantly increased the surface hardness of Ti-6Al-4V alloy up to three–five times. The coated specimens demonstrated superior wear resistance compared to the uncoated, with the −150 V specimen exhibiting the least wear rate. Furthermore, the −150 V specimen had the highest polarization impedance value, indicating the best corrosion resistance compared to the other bias conditions. In short, the use of CAD-coated TiN/CrN multilayer film enhanced the surface properties of Ti-6Al-4V alloy, with the best wear and corrosion resistance achieved at −150 V bias. These novel findings have significant implications for improving the performance and durability of Ti-6Al-4V alloy components in various industrial applications.

A GaN-HEMT Active Drain-Pumped Mixer for S-Band FMCW Radar Front-End Applications.

This paper reports for the first time a drain-pumped (DP) mixer using Gallium Nitride (GaN) HEMT technology. Specifically, it describes a method aimed to predict the optimum bias conditions for active DP-mixers, leading to high conversion gain (CG) and linearity, along with the efficient use of the local oscillator drive level. A mixer prototype was designed and fabricated according to the discussed design principles; it exhibited a CG and an input third-order intercept point (IIP3) of +10dB and +11dBm, respectively, with a local oscillator power level of 20 dBm at about 3.7 GHz. In terms of gain and linearity, both figures exceed the documented limitations for the class of mixers considered in this work. To the authors' best knowledge, this is the first DP mixer operating in the S-band. The prototype was also tested in a radar-like setup operating in the S-band frequency-modulated continuous-wave (FMCW) mode. Measurements carried out in the radar setup resulted in +39.7dB and +34.7dB of IF signal-to-noise-ratio (SNR) for the DP and the resistive mixers, respectively. For comparison purposes, a resistive mixer was designed and fabricated using the same GaN HEMT technology; a detailed comparison between the two topologies is discussed in the paper, thus further highlighting the capability of the DP-mixer for system applications.

Heterogeneously integrated light emitting diodes and photodetectors in the metal-insulator-metal waveguide platform

Abstract We demonstrate heterogeneous integration of active semiconductor materials into the conventional passive metal-insulator-metal (MIM) waveguides to provide compact on-chip light generation and detection capabilities for chip-scale active nanophotonic platforms. Depending on its bias conditions, a metal-semiconductor-metal section can function as either a light emitting diode or a photodetector directly connected to the MIM waveguides. We experimentally verify the independent and combined operations of electrically-driven on-chip light sources and photodetectors.

Characterizing and Modeling RTN Under Real Circuit Bias Conditions

Random telegraph noise (RTN) has attracted much attention, as it becomes higher for smaller devices. Early works focused on RTN in linear drain current, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> , and there is only limited information on RTN in saturation current, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{SAT}}$</tex-math> </inline-formula> . As transistors can operate in either linear or saturation modes, lack of RTN model in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{SAT}}$</tex-math> </inline-formula> prevents modeling RTN for real circuit operation. Moreover, circuit simulation requires both driving current and threshold voltage, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\text{TH}}$</tex-math> </inline-formula> . A common practice of early works is to evaluate the RTN in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\text{TH}}$</tex-math> </inline-formula> by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH}}= \Delta \textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{g}_{\textit{m}}$</tex-math> </inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{g}_{\textit{m}}$</tex-math> </inline-formula> is the transconductance. It has been reported that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH}}$</tex-math> </inline-formula> evaluated in this way significantly overestimates the real <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH}}$</tex-math> </inline-formula> , but there is little data for establishing the cumulative distribution function (CDF) of the real <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH}}$</tex-math> </inline-formula> . An open question is whether <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH}}$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> follow the same CDF. The objectives of this work are threefold: to provide statistical test data for RTN in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{SAT}}$</tex-math> </inline-formula> ; to measure the RTN in real <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH}}$</tex-math> </inline-formula> by pulse <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D}}$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\textit{G}}$</tex-math> </inline-formula> ; and, for the first time, to apply the integral methodology for developing the CDF per trap for all four key parameters needed by circuit simulation— <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{I}_{\textit{D},\text{SAT}}$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{SAT}}$</tex-math> </inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH,\text{LIN}}}$</tex-math> </inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH,\text{SAT}}}$</tex-math> </inline-formula> . It is found that the log-normal CDF is the best for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{I}_{\textit{D},\text{SAT}}$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{SAT}}$</tex-math> </inline-formula> , while the general extreme value CDF is the best for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH,\text{LIN}}}$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH,\text{SAT}}}$</tex-math> </inline-formula> . Both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{I}_{\textit{D},\text{SAT}}$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{SAT}}$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{V}_{\text{TH,\text{SAT}}}$</tex-math> </inline-formula> are higher than their linear counterparts and separate modeling is required. Finally, the applicability of integral methodology in predicting the long term <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{D},\text{LIN}}$</tex-math> </inline-formula> is demonstrated.

Room Temperature Light Emission from Superatom-like Ge-Core/Si-Shell Quantum Dots.

We have demonstrated the high-density formation of super-atom-like Si quantum dots with Ge-core on ultrathin SiO2 with control of high-selective chemical-vapor deposition and applied them to an active layer of light-emitting diodes (LEDs). Through luminescence measurements, we have reported characteristics carrier confinement and recombination properties in the Ge-core, reflecting the type II energy band discontinuity between the Si-clad and Ge-core. Additionally, under forward bias conditions over a threshold bias for LEDs, electroluminescence becomes observable at room temperature in the near-infrared region and is attributed to radiative recombination between quantized states in the Ge-core with a deep potential well for holes caused by electron/hole simultaneous injection from the gate and substrate, respectively. The results will lead to the development of Si-based light-emitting devices that are highly compatible with Si-ultra-large-scale integration processing, which has been believed to have extreme difficulty in realizing silicon photonics.

Effect of bias conditions on transient anode current for quasi-double-sided silicon drift detector with high energy resolution

Silicon drift detectors (SDDs) are widely applied for x-ray detection due to their remarkable energy resolution. The main contribution to energy resolution is the electrical noise of the measurement system. In addition, imperfect charge collection and ballistic deficits also deteriorate the energy resolution, which is closely related to bias conditions. However, bias condition's effect on energy resolution has been rarely reported. To investigate its effect on energy resolution, we proposed a quasi-double-sided silicon drift detector (QD-SDD) with a drift ring structure designed on the back side. QD-SDDs was simulated and verified to have more flexibility in bias conditions, achieving better electron collection efficiency and shorter collection time at higher bias voltages. Finally, the fabricated QD-SDDs were characterized using a55Fe radioactive source. The experimental results show that the energy resolution of the QD-SDD varies with different bias conditions. The optimal energy resolution is 170 eV under the optimized bias conditions.

Investigation on the non-linear behaviour of silicon nanowires and assessment of the biosensing potential

We perform a rigorous study on the conduction characteristics of long, low doped and relatively thick p-type silicon nanowire (SiNW) with different bias polarities/strengths to find out the origin of the non-linear electrical characteristics and to find out the applicable bias window for ensuring the gate responsive operation as biosensor. Depending on the polarity and strength of the drain bias (VDS)/liquid gate voltage (VGS), conduction is found to be confined in the bulk, in the surface accumulation region or in a path that comprises both accumulation region and the bulk thereby results in the diode or transistor like non-linear output characteristics. Although the SiNW is long without any junctions in the source/drain, the transfer characteristics exhibits a distinct shift with the increase of VDS when VDS is positive. The non-linear characteristics of SiNW is analysed to extract the gate responsive biasing window and it is found that the positive VDS application provides the flexibility of choosing diverse range of VDS and VGS voltages. As such, the shift in the transfer characteristic which is not appreciated for logic operation appears to be beneficiary for nanowire biosensors. This study sheds light on the variable electrical characteristics of SiNW reported in the literature and shows the way to choose appropriate bias conditions for biosensing applications.

Heterostructure axial GaAsSb ensemble near-infrared p–i–n based axial configured nanowire photodetectors

In this work, we present a systematic design of growth experiments and subsequent characterization of self-catalyzed molecular beam epitaxially grown GaAsSb heterostructure axial p–i–n nanowires (NWs) on p-Si <111> for the ensemble photodetector (PD) application in the near-infrared region. Diverse growth methods have been explored to gain a better insight into mitigating several growth challenges by systematically studying their impact on the NW electrical and optical properties to realize a high-quality p–i–n heterostructure. The successful growth approaches are Te-dopant compensation to suppress the p-type nature of intrinsic GaAsSb segment, growth interruption for strain relaxation at the interface, decreased substrate temperature to enhance supersaturation and minimize the reservoir effect, higher bandgap compositions of the n-segment of the heterostructure relative to the intrinsic region for boosting the absorption, and the high-temperature ultra-high vacuum in situ annealing to reduce the parasitic radial overgrowth. The efficacy of these methods is supported by enhanced photoluminescence (PL) emission, suppressed dark current in the heterostructure p–i–n NWs accompanied by increased rectification ratio, photosensitivity, and a reduced low-frequency noise level. The PD fabricated utilizing the optimized GaAsSb axial p–i–n NWs exhibited the longer wavelength cutoff at ∼1.1 μm with a significantly higher responsivity of ∼120 A W−1 (@−3 V bias) and a detectivity of 1.1 × 1013 Jones operating at room temperature. Frequency and the bias independent capacitance in the pico-Farad (pF) range and substantially lower noise level at the reverse biased condition, show the prospects of p–i–n GaAsSb NWs PD for high-speed optoelectronic applications.

Influence of applied bias on direct conversion X-ray sensing capability of nanocrystalline Ca9Ag(PO4)6(OH)2

Silver (Ag) doping in hydroxyapatite (HAP) can enhance the attenuation coefficient (μ) 0.65 cm2/g at photon energy 70 keV as compared with pure hydroxyapatite (μ = 0.31 cm2/g). In this study, direct conversion X-ray sensors were fabricated using pure HAP (Ca10(PO4)6(OH)2) and Ag-doped HAP (Ca9Ag(PO4)6(OH)2) to realize superior X-ray sensing capability. Thick films of wet-chemical route derived nanocrystalline samples were deposited on interdigitated electrodes by glass rod sliding technique and its X-ray instigated photocurrent characteristics at 2 V biased condition were recorded for different low doses (mGy). The observed sensitivity at 7.97 mGy dose reveals ten folds enhancement from 0.19 nC/mGy cm3 to 1.00 nC/mGy cm3. According to the “Grain boundary double Schottky potential barrier height model”, the formation of potential barrier height (φb) at the interface of grain and grain boundaries of nanocrystalline samples is identical to the Schottky barrier. By increasing the applied bias, the conduction band starts to bend and suppresses the potential barrier height (φb). In higher biased conditions, φb does not exist. Hence, the influence of applied bias on direct conversion X-ray sensing capability of Ca9Ag(PO4)6(OH)2 was investigated and discussed in detail.

High efficient PEC performance via mechanical stress field and temperature field coupling assisted Ba0·7Sr0·3TiO3 under visible light irradiation

Limited carriers migration and separation efficiency are key factors affecting the photo-electric catalysis performance of semiconductors. In this paper, the mechanical stress field and temperature field are combined to realize the piezo-pyro-photo-electric catalysis by using the coupling effect of the two external fields, which greatly improves the catalysis performance of Ba0·7Sr0·3TiO3 semiconductor. At 20–50 °C alternating heating and cooling, ultrasonic excitation, light and bias conditions, the current density of Ba0·7Sr0·3TiO3 increased to 1.01 mA cm−2. It is 1.22 and 1.31 times higher than that of piezo-photo-electric catalysis (0.83 mA cm−2) under single mechanical stress field and pyro-photo-electric catalysis (0.77 mA cm−2) under temperature field, respectively. The coupled external stimulation is beneficial to the improvement of photo-electric catalysis performance. Due to the presence of polarization charge imbalance and piezoelectric/pyroelectric polarization induced built-in electric field piezoelectric/pyroelectric potential, thereby increasing the total concentration of carriers, accelerating the separation and transfer efficiency of carriers. This study realizes the synergistic utilization of various clean energy sources such as solar energy, thermal energy, mechanical energy and electrical energy, and provides a key idea for designing electrodes with excellent catalytic performance.

Enhanced low-dose x-ray sensing nature of nanocrystalline CaWO4 sensor

Extensive research on the development of superior sensitive X-ray sensors by many researchers is due to their increased demand in numerous fields, like medical radiography, security inspection, and scientific research areas. Especially in healthcare, repeated or long-term high-dose X-ray exposure on patients may cause serious health hazards. Therefore, developing a superior sensing low dose X-ray sensor is essential. In this present work, a nanocrystalline CaWO4 thick film above an interdigitated electrode was developed as a direct conversion X-ray sensor that operates at different low doses (mGy) using an intraoral pulsed X-ray (70 keV) machine. The X-ray instigated photocurrent of nano-CaWO4 thick film was examined under different applied bias to obtain superior sensitivity of the device. The nano-CaWO4 thick film exhibit sensitivity of 10 nC/mGycm3 at 0.20 mGy (0.06 s) low dose under 5 V applied bias. A suitable mechanism was proposed to explain the nano-CaWO4 thick film sensing behaviour at different biased conditions.

Quad Port Multipolarized Reconfigurable MIMO Antenna for Sub 6 GHz Applications

Recent reconfigurable technological advancements for wireless communication systems provide various global solutions. This research work presents a quad port multipolarized switchable multiple input multiple output (MIMO) antenna for sub 6 GHz applications. It covers the frequency range from 3.1 to 5.1 GHz, including the 5G NR band n78 (3.3 to 3.8 GHz) and 5G NR band n79 (4.4 to 5 GHz). The proposed antenna comprises four offset-fed monopole antenna elements with an overall dimension of 60 mm × 65 mm. To achieve circular polarization (CP), a parasitic meandering resonator is integrated with antenna elements using four PIN diodes. The polarization diversity is obtained by controlling the bias states of four PIN diodes. The radiating element −1/−3 offers left hand circular polarization (LHCP), while element −2/−4 procures right hand circular polarization (RHCP) when all diodes are ON. Consequently, the proposed antenna provides linear polarization (LP) under reverse bias conditions. Moreover, the designed antenna acquires a wide axial ratio bandwidth (ARBW) of 36.1%. In addition, the developed MIMO antenna exhibits isolation greater than 15 dB using the common ground plane, and the obtained ECC is less than 0.13. The prototype is fabricated, and the simulated responses are in good correlation with the measured results.

Look-alike Landau levels in locally biased twisted bilayer graphene

Large lattice constant of Moire superlattice formed in twisted bilayer graphene enables observing Landau levels splitting into Hofstadter butterflies. This is expected for homogeneous bias conditions but its robustness against spatial potential fluctuations is left open question. We study the energy structure of twisted bilayer system in dependence of both, homogeneous magnetic field and bias voltage applied in its central region. Although translational symmetry is broken, the energy states localized outside the biased region still form Landau levels revealing self-similarity feature. Moreover, besides generic Landau levels appearing when both layers are biased with the same voltage, the second look-alike energy branch can be developed by states largely localized in central biased region. Otherwise, for counter-biasing of layers, only generic branch exists but with lowest Landau levels flanked by either, hole-like and electron-like states localized at the top or at the bottom layer of central biased part of twisted bilayer system.

Dinosaur fauna from the Lower Cretaceous of Phu Kao-Phu Phan Kham, northeastern Thailand: a review and update

Phu Kao-Phu Phan Kham Mountain ranges, situated on the border of Nong Bua Lamphu, Udon Thani, and Khon Kaen provinces, northeastern Thailand, bear several localities that yield dinosaurs and other vertebrate faunas in the Lower Cretaceous. However, this area has received relatively little attention from the scientific community and the public. Here we review and report new dinosaur materials recovered from this region, some found decades ago, others discovered recently. We identify and discuss their taxonomy and paleobiodiversity. In the Barremian Sao Khua Formation, theropod dinosaurs were represented by spinosaurids, an early branching megaraptoran, a large indeterminate theropod, and small indeterminate theropods. Sauropods were represented by an indeterminate sauropod, a neosauropod, and titanosauriforms, including probable brachiosaurid and non-titanosaur somphospondylans. Other vertebrate groups, including crocodilians, turtles, fishes, and sharks, indicate a similar composition to other Sao Khua Formation communities in northeastern Thailand. The Sao Khua vertebrate assemblage exhibits the taxonomic diversity of dinosaur fauna and is currently the best-documented assemblage in the Early Cretaceous of Southeast Asia. The Aptian–Albian Khok Kruat Formation, however, yields less diverse vertebrates. They are represented by freshwater sharks, crocodilians, and spinosaurid theropods. This may be due to sampling bias, environmental, or taphonomic conditions. This study provides the basis for future paleontological exploration and research of Mesozoic vertebrates in northeastern Thailand.

Adaptive Bitline Voltage Countermeasure for Neighbor Wordline Interference in 3D NAND Flash Memory-Based Sensors.

Three-dimensional NAND flash memory is widely used in sensor systems as an advanced storage medium that ensures system stability through fast data access. However, in flash memory, as the number of cell bits increases and the process pitch keeps scaling, the data disturbance becomes more serious, especially for neighbor wordline interference (NWI), which leads to a deterioration of data storage reliability. Thus, a physical device model was constructed to investigate the NWI mechanism and evaluate critical device factors for this long-standing and intractable problem. As simulated by TCAD, the change in channel potential under read bias conditions presents good consistency with the actual NWI performance. Using this model, NWI generation can be accurately described through the combination of potential superposition and a local drain-induced barrier lowering (DIBL) effect. This suggests that a higher bitline voltage (Vbl) transmitted by the channel potential can restore the local DIBL effect, which is ever weakened by NWI. Furthermore, an adaptive Vbl countermeasure is proposed for 3D NAND memory arrays, which can significantly minimize the NWI of triple-level cells (TLC) in all state combinations. The device model and the adaptive Vbl scheme were successfully verified by TCAD and 3D NAND chip tests. This study introduces a new physical model for NWI-related problems in 3D NAND flash, while providing a feasible and promising voltage scheme as a countermeasure to optimize data reliability.

Amplifying Student and Administrator Perspectives on Equity and Bias in Learning Analytics

When higher education institutions (HEIs) have the potential to collect large amounts of learner data, it is important to consider the spectrum of stakeholders involved with and impacted by the use of learning analytics. This qualitative research study aims to understand the degree of concern with issues of bias and equity in the uses of learner data as perceived by students, diversity and inclusion leaders, and senior administrative leaders in HEIs. An interview study was designed to investigate stakeholder voices that generate, collect, and utilize learning analytics from eight HEIs in the United States. A phased inductive coding analysis revealed similarities and differences in the three stakeholder groups regarding concerns about bias and equity in the uses of learner data. The study findings suggest that stakeholders have varying degrees of data literacy, thus creating conditions of inequality and bias in learning data. By centring the values of these critical stakeholder groups and acknowledging that intersections and hierarchies of power are critical to authentic inclusion, this study provides additional insight into proactive measures that institutions could take to improve equity, transparency, and accountability in their responsible learning analytics efforts.