Limit Of Thickness Research Articles

Diffusion Limit–Preserving Lumped DFEMs on AMR Meshes

We present sweep-compatible, novel upwinding recipes for the bilinear discontinuous (BLD) finite element method (FEM) that allows lumped BLD to be used on adaptive mesh refinement (AMR) meshes for thick transport applications without adding additional degrees of freedom at hanging nodes that exist on refinement boundaries. We analyze the properties of the upwinding and lumping that are needed for BLD to get the thick diffusion limit on such meshes, present results demonstrating locking with the wrong recipe, and present results showing error convergence and robustness properties for two diffusive problems on a variety of AMR meshes.

Determination of model parameters under sharp and thin interface limits of the phase-field model to study cation interdiffusion in SOFC

A systematic procedure is presented to determine the gradient energy coefficient and height of double-well potential (phase-field model parameters). The well-known Allen-Cahn equation is used to investigate cation interdiffusion in solid oxide fuel cell (SOFC). An established procedure that commonly applied in the study of solidification is adapted. The phase-field model parameters are determined under sharp as well as thin interface limits. The upper limit of the interface thickness is deduced for the thin interface limit. Effect of variation of interface thickness for a particular value of interfacial energy is evaluated on the cation interdiffusion in terms of interdiffusion length of the cations under thin interface limit and this is compared with that of sharp interface limit. Effect of variation of interfacial energy at the upper limit of the interface thickness is also studied under the thin interface limit. Further, the reason behind the variation of interdiffusion length is also presented under the thin interface limit for different values of interfacial energy. Under a large variation of interfacial energy, no significant changes are found in the interdiffusion length of the cations. From this study, it can be deduced that for a considerable range of interfacial energy, a wider range of model parameters can be selected for the phase-field model with reasonable accuracy.

Singularity formation of vortex sheets in two-dimensional Euler equations using the characteristic mapping method

The goal of this numerical study is to get insight into singular solutions of the two-dimensional (2D) Euler equations for nonsmooth initial data, in particular for vortex sheets. To this end, high resolution computations of vortex layers in two-dimensional incompressible Euler flows are performed using the characteristic mapping method (CMM). This semi-Lagrangian method evolves the flow map using the gradient-augmented level set method. The semigroup structure of the flow map allows its decomposition into submaps (each over a finite time interval), and thus, the precision can be controlled by choosing appropriate remapping times. Composing the flow map yields exponential resolution in linear time, a unique feature of CMM, and thus, fine-scale flow structures can be resolved in great detail. Here, the roll-up process of vortex layers is studied varying the thickness of the layer showing its impact on the growth of palinstrophy and possible blow up of absolute vorticity. The curvature of the vortex sheet shows a singular-like behavior. The self-similar structure of the vortex core is investigated in the vanishing thickness limit. Conclusions on the presence of posssible singularities of two-dimensional Euler equations for nonsmooth initial data are drawn by tracking them in the complex plane.

(Invited) Atomic-Scale Design of Advanced Transistors Via Ultrathin Negative Capacitance Gate Stacks

Negative capacitance [1,2] has emerged as a promising solution to overcome fundamental energy-efficiency limits in conventional electronics, in which internal ferroelectric order within the gate stack of a field-effect transistor can enable low-power operation. Thus far, claims of negative capacitance have been primarily demonstrated in perovskite-structure thick films or through misleading “S-curve” transient experiments in fluorite-structure thick films. However, integration into advanced semiconductor technology nodes will require stabilization at the ultrathin regime and evidence of capacitance enhancement (i.e. lower equivalent oxide thickness, EOT) to enable highly-scaled lower-power operation.Here, we present evidence of negative capacitance in atomic-scale HfO2-ZrO2 heterostructures down to two-nanometers and one-nanometer thickness [3,4], leveraging our recent work examining the atomic limits of fluorite-structure ferroelectricity on silicon [5,6]. ALD HfO2-ZrO2-based heterostructures on Si-SiO2 demonstrate ultralow EOT without having to scavenge the SiO2 interlayer, in stark contrast to conventional high-κ metal gate (HKMG) technology [7]. Accordingly, in comparison to industrial HKMG benchmarks, these SiO2-buffered antiferroelectric-ferroelectric gate stacks boast favorable performance and can provide multiple node technology boosts [8]. Due to seamless integration and transition from high-κ HfO2-based dielectrics to negative-κ HfO2-ZrO2-based ferroelectrics, these NC stacks have already been validated and integrated by prototyping foundries [8] and semiconductor foundries [9].In this talk, key differences between static versus transient negative capacitance will be highlighted to clarify misleading literature and explain their relative benefits for logic transistors [3,4] versus other applications [10]. Perspectives on further routes to EOT scaling via negative capacitance gate stacks for beyond-1-nm-node logic technology will also be discussed. R Landauer. “Can capacitance be negative.” Collect. Phenom. 2, 167–170 (1976).S Salahuddin & S Datta. “Can the subthreshold swing in a classical FET be lowered below 60 mV/decade?” in 2008 IEEE International Electron Devices Meeting (IEEE, 2008).S Cheema et al. “Ultrathin ferroic HfO2–ZrO2 superlattice gate stack for advanced transistors.” Nature 604, 65–71 (2022).S Cheema et al. “Physical and electric thickness limits of negative capacitance.” In preparation (2024).S Cheema et al. “Emergent ferroelectricity in subnanometer binary oxide films on silicon.” Science 376, 648–652 (2022).S Cheema et al.“Enhanced ferroelectricity in ultrathin films grown directly on silicon.” Nature 580, 478–482 (2020).T Ando “Ultimate Scaling of High-κ Gate Dielectrics: Higher-κ or Interfacial Layer Scavenging?” Materials 5, 478–500 (2012).N Shanker et al. “CMOS Demonstration of Negative Capacitance HfO2-ZrO2 Superlattice Gate Stack in a Self-Aligned, Replacement Gate Process.” in 2022 International Electron Devices Meeting (IEDM) 34.3.1-34.3.4 (IEEE, 2022).S Jo. et al. “Negative differential capacitance in ultrathin ferroelectric hafnia.” Nat. Electron. 6, 390–397 (2023).S Cheema et al.“Giant energy storage and power density negative capacitance superlattices.” Nature doi:10.1038/s41586-024-07365-5 (2024).

COMPARISON OF CHOROIDAL VASCULATURE BETWEEN CENTRAL SEROUS CHORIORETINOPATHY WITH AND WITHOUT THICK CHOROID USING SWEPT-SOURCE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY.

To distinguish between central serous chorioretinopathy (CSC) with and without thick choroid and to elucidate their characteristics of choroidal vasculature. This prospective observational study enrolled 76 eyes with treatment-naive CSC and 76 normal eyes. Mean + 2 times SD of subfoveal choroidal thickness of healthy individuals was set as the upper limit of normal choroidal thickness to divide patients with CSC into two groups: the thick-choroid and non-thick-choroid groups. Their choroid blood flow was compared using widefield swept-source optical coherence tomography angiography. According to the discrimination value of subfoveal choroidal thickness as 326.8 µm, 76 eyes with CSC were divided into the thick-choroid (55, 72.4%) and non-thick-choroid (21, 27.6%) groups. Higher proportions of vortex vein anastomosis were found in the thick-choroid group (81.8% vs. 33.3%, P < 0.001). Choroid thickness, three-dimensional choroidal vascularity index, and mean choroidal stroma volume per 1 mm2 were higher in the thick-choroid group. In multivariate analysis, younger age, higher percentages of vortex vein anastomosis, and double layer sign were the independent predictors of choroid thickening in CSC. There are discrepancies in the degree of choroidal congestion and distribution of vortex veins in the CSC with different choroidal thicknesses.

Self-Supervised Learning for Generic Raman Spectrum Denoising.

Raman and surface-enhanced Raman scattering (SERS) spectroscopy are highly specific and sensitive optical modalities that have been extensively investigated in diverse applications. Noise reduction is demanding in the preprocessing procedure, especially for weak Raman/SERS spectra. Existing denoising methods require manual optimization of parameters, which is time-consuming and laborious and cannot always achieve satisfactory performance. Deep learning has been increasingly applied in Raman/SERS spectral denoising but usually requires massive training data, where the true labels may not exist. Aiming at these challenges, this work presents a generic Raman spectrum denoising algorithm with self-supervised learning for accurate, rapid, and robust noise reduction. A specialized network based on U-Net is established, which first extracts high-level features and then restores key peak profiles of the spectra. A subsampling strategy is proposed to refine the raw Raman spectrum and avoid the underlying biased interference. The effectiveness of the proposed approach has been validated by a broad range of spectral data, exhibiting its strong generalization ability. In the context of photosafe detection of deep-seated tumors, our method achieved signal-to-noise ratio enhancement by over 400%, which resulted in a significant increase in the limit of detection thickness from 10 to 18 cm. Our approach demonstrates superior denoising performance compared to the state-of-the-art denoising methods. The occlusion method further showed that the proposed algorithm automatically focuses on characterized peaks, enhancing the interpretability of our approach explicitly in Raman and SERS spectroscopy.

Pushing the Thickness Limit of the Giant Rashba Effect in Ferroelectric Semiconductor GeTe.

Ferroelectric Rashba semiconductors (FERSCs) such as α-GeTe are promising candidates for energy-efficient information technologies exploiting spin-orbit coupling (SOC) and are termed spin-orbitronics. In this work, the thickness limit of the Rashba-SOC effect in α-GeTe films is investigated. We demonstrate, using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations performed on pristine GeTe, that down to 1 nm, GeTe(111) films on a Sb-covered Si(111) substrate continuously exhibit a giant Rashba effect characterized, at 1 nm, by a constant of 5.2 ± 0.5 eV·Å. X-ray photoemission spectroscopy (XPS) allows the understanding of the persistence of the Rashba effect by evidencing a compensation of Ge vacancy defects resulting from the insertion of Sb interfacial atoms in the early stage growth of the GeTe(111) films.

Factors Influencing Measurement of Dynamic Elastic Modulus from Disk-Shaped Concrete Specimen

The decrease in dynamic elastic modulus is a primary indicator of quantitative damage in concrete. To quantitatively assess depth-by-depth damage within a concrete structure, cylindrical specimens obtained through coring can be cut into disk specimens to measure the dynamic elastic modulus of concrete at each depth. To minimize external damage during coring, it is essential to extract cylinders with the smallest possible diameter. In addition, for higher resolution in depth-based damage assessment, creating disk specimens with the smallest possible thickness is necessary. However, there is no information available in the literature on experimental limitation of smallest possible diameter and thickness for dynamic elastic modulus of disk-shaped specimens. This study evaluated whether the dynamic modulus measured from various sizes of concrete disk specimens provided sufficient reliability compared to reference values obtained from cylinders. Moreover, the study examined how the presence of coarse aggregate and variation in the water–cement ratio significantly influenced the dynamic modulus measurement. In addition, test results from impulse excitation technique (IET) and impact resonance (IR) were compared to find a more reliable test method for dynamic elastic modulus of disk specimen. The experimental findings revealed that as the thickness-to-radius ratio of the disk specimens decreased, measured data variation increased. Mortar specimens without coarse aggregates showed less variability compared to concrete specimens, and the variation in dynamic modulus measured by IR was lower than that measured by IET.

Determination of thermal conductivity of phase pure 10H-SiC thin films by non-destructive Raman thermometry

The 10 H SiC thin films are potential candidates for devices that can be used in high temperature and high radiation environment. Measurement of thermal conductivity of thin films by a non-invasive method is very useful for such device fabrication. Micro-Raman method serves as an important tool in this aspect and is known as Raman thermometry. It utilises a steady-state heat transfer model in a semi-infinite half space and provides for an effective technique to measure thermal conductivity of films as a function of film thickness and laser spot size. This method has two limiting conditions i.e. thick film limit and thin film limit. The limiting conditions of this model was explored by simulating the model for different film thicknesses at constant laser spot size. 10H SiC films of three different thicknesses i.e. 104, 135 and 156 nm were chosen to validate the thin film limiting condition. Thermal conductivity of these thin films varied from 0.60 – 4.80 (Wm−1K−1).

A Thin Film Model for Meniscus Evolution

In this paper, we discuss a particular model arising from sinking of a rigid solid into a thin film of liquid, i.e. a liquid contained between two solid surfaces and part of the liquid surface is in contact with the air. The liquid is governed by Navier–Stokes equation, while the contact point, i.e. where the gas, liquid and solid meet, is assumed to be given by a constant, non-zero contact angle. We consider a scaling limit of the liquid thickness (lubrication approximation) and the contact angle between the liquid–solid and the liquid–gas interfaces close to π\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\pi $$\\end{document}. This resulting model is a free boundary problem for the equation ht+(h3hxxx)x=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$h_t + (h^3h_{xxx})_x = 0$$\\end{document}, for which we have h>0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$h>0$$\\end{document} at the contact point (different from the usual thin film equation with h=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$h=0$$\\end{document} at the contact point). We show that this fourth order quasilinear (non-degenerate) parabolic equation, together with the so-called partial wetting condition at the contact point, is well-posed. Furthermore, the contact point in our thin film equation can actually move, contrary to the classical thin film equation for a droplet arising from the no-slip condition. Additionally, we show the global stability of steady state solutions in a periodic setting.

Enhancing microstructural integrity and mechanical performance of thick wire-arc directed energy deposited eutectic aluminum-silicon solid structure through continuous multi-pass friction stir processing

In wire-arc directed energy deposition (waDED), fabricating larger 3D components with single-layer tracks is challenging due to limitations in track thickness, requiring the development of bead overlapping strategies. However, fusion-based 3D-printed aluminum structures often show porosity and coarse-grained microstructures, limiting their industrial applications. To address these limitations, this study employs continuous multi-pass friction stir processing (FSP) on a waDED-produced aluminum block (140 mm × 150 mm × 28 mm). The severe plastic deformation induced by FSP triggers dynamic recrystallization (DRX), promoting the formation of equiaxed grains with an average grain size 8.75 times smaller than the as-fabricated waDED sample (67.03 μm vs 7.66 μm). Transmission Electron Microscopy (TEM) revealed decreased dislocation loops post-FSP, indicating DRX and dislocation annihilation. X-ray micro-computed tomography (X-CT) examination showed complete elimination of porosity in the waDED sample, owing to the intense mechanical stirring induced during FSP. Scanning electron microscopy (SEM) images of the waDED samples showed fibrous eutectic networks disrupted by FSP, leading to a uniform distribution of broken Si particles within the α-Al matrix. Hardness decreased by approximately 38 % (86 HV0.1 vs 53 HV0.1), while the average ultimate tensile strength decreased by about 4 % in the FSP-treated samples (159.19 MPa vs 153.02 MPa). Additionally, the formation of alpha fiber and weak cube texture components during FSP enhances ductility, as evidenced by a sixfold improvement in elongation (1.93 % vs 11.59 %). This textural transformation contributes to the characteristic deeper and more uniform dimples in the FSP-treated samples, indicative of ductile fracture, compared to the premature failure patterns in as-deposited samples.

Giant Tunneling Electro‐Resistance in Ultrathin Ferroelectric Tunnel Junctions: The Interface Barrier Gain Mechanism

AbstractUltrathin ferroelectric tunnel junctions (FTJs) hold considerable promise for next‐generation, high‐speed, low‐power, and high‐density nonvolatile memory applications. Achieving a substantial tunneling electro‐resistance (TER) remains a challenge as the ferroelectric layer is thinned to nanoscale dimensions, often resulting in a diminished or lost polarization. An innovative interface barrier gain mechanism is introduced, employing interface electronic state modulation to precisely control the size of an additional interface barrier. This strategy lessens the dependency of the tunneling barrier on ferroelectric polarization strength, facilitating a remarkable TER even at ferroelectric thicknesses as minimal as ≈1 nm. The focus is on composite FTJs using In2Se3/MTe2 (M = Mo, W), where the inclusion of an MTe2 monolayer disrupts the asymmetric electrode configuration. The weak ferroelectric polarization reversal of the In2Se3 monolayer effectively modulates the electronic state coupling at the In2Se3/MTe2 interface. This modulation leads to variations in the width and height of the Schottky barrier at the heterojunction‐electrode interface corresponding with the ferroelectric polarization reversal, establishing a beneficial Ohmic contact in the “on” state and resulting in an exponential TER increase up to 5.4 × 106%. This work introduces a universal mechanism to overcome the thickness limitations traditionally associated with enhancing TER, marking a significant advancement in the development of ultrathin ferroelectric nonvolatile devices.

The interdependence of functional properties of a football boot outsole during the shape optimisation process

The aim of this study was to investigate the relationship and interdependence of functional properties of the football boot outsole during the shape optimisation process. Sensitivity-based shape optimisation technique was applied to a football boot outsole to modify its thickness to have various functional properties. Three functional properties of the outsole, which are the midfoot and forefoot bending stiffness and torsional stiffness, were investigated. The midfoot and forefoot bending stiffness were measured via a three-point bending test. Torsional stiffness was measured via a bespoken mechanical test. The functional properties were evaluated by finite element models, representing the developed mechanical tests. Through the optimisation tasks, it was explored how much each functional property could be changed individually and also while minimising the influence of the other two functional properties. With the modification of the regions of the outsole to optimise for various individual target functional property values, the changes in the other two functional properties were observed. Lastly, the optimised outsoles from the finite element models were 3D printed and tested to determine the accuracy of the process. Within a permitted thickness limit, modifying the region associated with the torsional stiffness measurement influenced the other two functional properties the most. Especially, the midfoot bending stiffness was influenced more than the forefoot bending stiffness. On the other hand, the areas involved in the midfoot and forefoot bending stiffness measurements were independent of each other. The conclusions drawn in this study are limited to the particular outsole design, single outsole component and mechanical test utilised.

Biofilm growth characteristic and footprint identification in gravity-driven ceramic membrane bioreactor with electro-coagulation under extreme conditions for roofing rainwater purification

The identification of biofilm growth footprints influencing on the biofilm detachment and breakup can advance research into how biofilms form. Thus, a gravity-driven ceramic membrane bioreactor (GDCMBR) was used to investigate the growth, detachment and breakup of biofilm using rainwater pretreated by electrocoagulation under 70-days continuous operation. The in-situ ultrasonic time-domain reflectometry (UTDR) technique was applied to non-invasively determine the biofilm thickness. Initially, the biofilm was slowly thickening, but it would collapse and became thinner after accumulating to a certain level, and then it thickened again in a later period, following a cyclic pattern of ‘thickening - collapsing – thickening’. This is because the biofilm growth is related with the accumulation of flocs, however, excessive floc formation results in the biofilm being overweight till reaching the thickness limit and thus collapsing. Subsequently, the biofilm gradually thickens again due to the floc production and continuous deposition. Although the biofilm was dynamically changing, the water quality of treatment of the biofilm always remained stable. Ammonia nitrogen and total phosphorus have been almost completely removed, while CODMn removal efficiency was around 25%. And total bacteria amount in the membrane concentrate was obviously higher than that in the influent with the greater microbial activity, demonstrating the remarkable enrichment effect on bacteria. The understanding of biofilm growth characteristic and footprint identification enables us to develop rational approaches to control biofilm structure for efficient GDCMBR performance and operation lifespan.

Chiral absorption enhancement via critically coupled resonances in atomically thin photonic crystal exciton-polaritons.

Atomically thin transition metal dichalcogenides (TMDS) offer a promising route to the scaling down of optoelectronic devices to the ultimate thickness limit. But the weak light-matter interaction caused by their atomically thin nature makes them inevitably rely on external photonic structures to enhance optical absorption. Here, we report chiral absorption enhancement in atomically thin tungsten diselenide (WSe2) using chiral resonances in photonic crystal (PhC) nanostructures patterned directly in WSe2 itself. We show that the quality factors (Q factors) of the resonances grow exponentially as the PhC thickness approaches atomic limit. As such, the strong interaction of high Q factor photonic resonance with the coexisting exciton resonance in WSe2 results into self-coupled exciton-polaritons. By balancing the light coupling and absorption rates, the incident light can critically couple to chiral resonances in WSe2 PhC exciton-polaritons, leading to the theoretically limited 50% optical absorptance with over 84% circular dichroism (CD).

Multi-Objective Deep Q-Network Control for Actively Lubricated Bearings

This paper aims to study and demonstrate the possibilities of using reinforcement learning for the synthesis of multi-objective controllers for radial actively lubricated hybrid fluid film bearings (ALHBs), which are considered to be complex multi-physical systems. In addition to the rotor displacement control problem being typically solved for active bearings, the proposed approach also includes power losses due to friction and lubricant pumping in ALHBs among the control objectives to be minimized by optimizing the lubrication modes. The multi-objective controller was synthesized using the deep Q-network (DQN) learning technique. An optimal control policy was determined by the DQN agent during its repetitive interaction with the simulation model of the rotor system with ALHBs. The calculations were sped up by replacing the numerical model of an ALHB with its surrogate ANN-based counterpart and by predicting the shaft displacements in response to operation of two independent control loops. The controller synthesized considering the formulated reward function for DQN agent is able to find a stable shaft position that reduces power losses by almost half compared to the losses observed when using a passive system. It also is able to prevent the established limit of the minimum fluid film thickness being exceeded to avoid possible system damage, for example, when the rotor is unbalanced during the operation. Analysis of the development process and the results obtained allowed us to draw conclusions about the main advantages and disadvantages of the considered approach, and also allowed us to identify some important directions for further research.

Opto-mechanical stacked metamaterials for optical readout millimeter wave detection

An opto-mechanical stacked metamaterials is proposed. Different from traditional metamaterials, it adopts a separable design to realize the stacked structure of the lower and upper chips. It can break the metamaterial thickness limit and integrate absorbing/execution units on functional layer with a thickness less than one thousandth of a wavelength, enabling high-performance detection. We design and prepare a millimeter wave opto-mechanical stacked metamaterial array detector, whose upper chip is only 1/2133 of the wavelength, but the absorptivity is about 99 %. Unlike the traditional detectors that convert millimeter wave radiation into electrical signals, it converts the radiation into micromechanical deflections opto-mechanical structures, and then reads them out optically. It’s equivalent to converting the millimeter wave detection into visible light detection. An optical readout system was constructed to verify the detection performance. Experimental results show that the response time can reach 20 ms and the NEP (Noise Equivalent Power) is 1.1 × 10−10 W/Hz1/2.

A Novel Q-Choked Resonator for Microwave Material Measurements Alleviating Sample Thickness Limitations of Existing Techniques

A Novel Q-Choked Resonator for Microwave Material Measurements Alleviating Sample Thickness Limitations of Existing Techniques

Micro-jetting: Areal density calculation from a triangular groove

We present a method for calculating the mass ejected during the reflection of a shock wave on a triangular groove. This calculation is based on the combination of two models taken from the literature, BMPT-2, on the one hand, for the calculation of the velocity and density of the jet, and fragmentation zone propagation (FZP ) on the other hand, for the calculation of the ejected mass, certain parameters required for FZP being determined by BMPT-2. Compared with previous work, FZP has been extended to deal with the various stages of jet formation. The approach was first evaluated on tin using a large-scale molecular dynamics simulation. This first step validated the overall phenomenology and the associated theoretical tools, and enabled us to propose a procedure for adjusting FZP. Next, we used the BMPT-2/FZP combination to analyze ejected mass measurement experiments using Asay foil. The areal mass curves are well reproduced with few parameters, showing that there is no inconsistency between BMPT-2/FZP and the experiments. Finally, a more detailed analysis of the results obtained enables us to set the limits of the jet thickness at the moment of rupture, and to propose a simple analytical form of its profile compatible with the model used.

Significantly improved optoelectronic performances of two-dimensional WS2(Er3+)/WSe2(Er3+) van der waals heterojunctions

Two-dimensional heterostructures with excellent properties are potential for high performance optoelectronic applications, since the ultimate thickness limit is possible to be broken with the advent of atomically thin materials. Yet the studies have also been largely constrained by the low physical doping space and absorption rates due to the atomic-thickness layers, and the efforts for high carrier concentrations and gain remain a significant challenge. Herein, high concentration of Er3+ ions are in-situ doped in WS2 and WSe2 atomic layers by chemical vapor deposition (CVD) method. The prepared layers are characterized by atomic force microscopy, transmission electron microscopy, photoluminescence (PL) spectroscopy, and Raman spectroscopy, respectively. 13–14 at% of Er3+ doping concentration in WSe2 and WS2 are examined by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) with high consistency. A microregion fixed-point transfer technique is used to transfer the WS2(Er3+) monolayers onto the WSe2(Er3+) monolayers to form vertical van der Waals heterojunctions. Excellent performances are measured from the WS2(Er3+)/WSe2(Er3+) photodetector with the photoresponsivity of up to 67.4 A/W, external quantum efficiency of 13,202 %, and detectivity of 7.07 × 1011 Jones. Our results prove the effectiveness of Er3+ in-situ doping in WS2(Er3+)/WSe2(Er3+) heterojunctions for high-performance photodetectors.