2D Scaling Research Articles

Electric Field Induced Electrorotation of 2D Perovskite Microplates.

High precision-controlled movement of microscale devices is crucial to obtain advanced miniaturized motors. In this work, we report a high-speed rotating micromotor based on two-dimensional (2D) all-inorganic perovskite CsPbBr3 microplates controlled via alternating-current (AC) external electric field. Firstly, the device configuration with optimized electric field distribution has been determined via systematic physical simulation. Using this optimized biasing configuration, when an AC electric field is applied at the four-electrode system, the microplates suspended in the tetradecane solution rotate at a speed inversely proportional to AC frequency, with a maximum speed of 16.4 × 2π rad/s. Furthermore, the electrical conductivity of CsPbBr3 microplates has been determined in a contactless manner, which is approximately 10−9–10−8 S/m. Our work has extended the investigations on AC electric field-controlled micromotors from 1D to 2D scale, shedding new light on developing micromotors with new configuration.

Spin-Dependent Transport at 2D Solids: From Nonmagnetic Layers to Ferromagnetic van der Waals Structures

Spintronics is a promising alternative to the conventional silicon transistor-based electronics that are gradually approaching their physical limitations. Ultrathin two-dimensional van der Waals (vdW) materials (2D materials) with controllable spin degrees of freedom are recognized as extremely promising spintronic materials in architectures for the post-Moore era. In this Perspective, we review recent progress on spin-dependent transport behaviors (SDTBs) confined at the 2D scale, which are the mainstream paradigms for spintronic devices. We first present the mechanism and the key factors of SDTBs in 2D nonmagnetic materials-based hybrid devices. Then, some chemical modulation strategies for inducing short-range magnetic order and magneto-electric performance into 2D nonmagnetic materials are discussed. Furthermore, we concentrate on introducing intriguing SDTBs in 2D long-range ferromagnetic materials-based vdW devices. Finally, we highlight the current challenges in the study of spin-dependent transport of 2D modified materials and 2D material-based spintronic devices, in the hope of accelerating their applications.

The 2D Future of 3D Electronics

CHRIS EDWARDS looks at how 2D scaling options could provide the basis for far more extensive 3D integration on the part of chipmakers

Observation of Scale Invariance in Two-Dimensional Matter-Wave Townes Solitons.

We report near-deterministic generation of two-dimensional (2D) matter-wave Townes solitons and a precision test on scale invariance in attractive 2D Bose gases. We induce a shape-controlled modulational instability in an elongated 2D matter wave to create an array of isolated solitary waves of various sizes and peak densities. We confirm scale invariance by observing the collapse of solitary-wave density profiles onto a single curve in a dimensionless coordinate rescaled according to their peak densities and observe that the scale-invariant profiles measured at different coupling constants g can further collapse onto the universal profile of Townes solitons. The reported scaling behavior is tested with a nearly 60-fold difference in soliton interaction energies and allows us to discuss the impact of a non-negligible magnetic dipole-dipole interaction (MDDI) on 2D scale invariance. We confirm that the effect of MDDI in our alkali cesium quasi-2D samples effectively conforms to the same scaling law governed by a contact interaction to well within our experiment uncertainty.

Structure, bonding nature and transition dynamics of amorphous Te

Te has drawn many interest due to the excellent electrical and optical performances in both bulk and 2D scale. Although amorphous phase usually generates some particular characteristics, relevant studies are still inadequate. By using ab initio molecular dynamics (AIMD) simulations, we have explored the dynamics and structure of Te during amorphization process. The large fraction of 2- and 3-coordinated Te results in an average coordination number of 2.43 in amorphous Te (a-Te), deviating from the “8-N rule”. The 2-coordinated chain structures and the 3- and 4-coordinated defective octahedral clusters, together with 25.3% voids, make a-Te a flexible and fragile glass. As a result, a mid-gap state is observed in the electronic density of states. Our study deepens the insight on a-Te, which is useful for the design of novel electronic and optical devices.

Two-dimensional [CaCl]+·e− with its strippable feasibility as an applicable electride with room-temperature ferromagnetism and extremely low work function

Electrides in a two-dimensional (2D) scale, especially those that capture inherent magnetism and have low work functions, have shown great application prospects in nanoscale spintronic devices and electronic emitters.

Regulating the carbon distribution of anode materials in lithium-ion batteries.

The exploration of electrode materials is considered to be a crucial process affecting the development of lithium-ion batteries. However, the large-scale commercial application of the great mass of anode materials has been hampered by the challenges with conductivity and volume change. These problems can be solved by the combination of a carbon-matrix with anode materials, which has proven to be an effective strategy. This review aims to outline recent advances in carbon-matrix composite anodes based on different dimensions (0D, 1D, 2D, 3D and atomic scale) and functions, with the emphasis on the regulation of carbon distribution of composite anodes. Besides, the matrix forms and carbon sources have also been summarized. This review will provide some light on the future carbon-matrix electrode design trends for LIBs.

Coherent control of individual electron spins in a two-dimensional quantum dot array.

The coherent manipulation of individual quantum objects organized in arrays is a prerequisite to any scalable quantum information platform. The cumulated efforts to control electron spins in quantum dot arrays have permitted the recent realization of quantum simulators and multielectron spin-coherent manipulations. Although a natural path to resolve complex quantum-matter problems and to process quantum information, two-dimensional (2D) scaling with a high connectivity of such implementations remains undemonstrated. Here we demonstrate the 2D coherent control of individual electron spins in a 3 × 3 array of tunnel-coupled quantum dots. We focus on several key quantum functionalities: charge-deterministic loading and displacement, local spin readout and local coherent exchange manipulation between two electron spins trapped in adjacent dots. This work lays some of the foundations to exploit a 2D array of electron spins for quantum simulation and information processing.

Numerical Investigation of 3D Distribution of Mining-Induced Fractures in Response to Longwall Mining

Extraction of coal mine methane is widely used in complex geological conditions. It does not only effectively prevent potential gas disasters, but it also alleviates energy crisis of the world. However, the high-efficiency extraction of coal mine methane is positively correlated with accurate positioning of mining-induced fracture-rich areas (relatively intensive fracture areas), which is yet to be fully understood (in particular on a 3D scale). In this paper, a simple fracture constitutive model was incorporated within a continuum code, and an innovative approach to fracture generation was proposed to get the fracture morphology. First, the code was tested against the uniaxial compression and true 3D experiments and it was shown to be capable of simulating fracture initiation and propagation on either 2D or 3D scale. This code then was used successfully to 3D longwall mining, and the numerical results were well in keeping with the field monitoring and physical modeling. The numerical results revealed that the fractured zones exhibit a 3D elliptic paraboloid shape, and mining-induced shear fractures, which dominated over the tensile fractures, had a 3D annular shape above the overlying strata, whereas a ribbon shape was observed for tensile fractures. A fracture-rich area was formed gradually at the center (exactly closer to the cut) above the gob, implying that the collapse mainly occurred in the gob roof rather than in the gob sidewall. The strengthening effect of mining-induced fractures on the permeability in longitudinal direction was markedly stronger than in transverse directions. The obtained results also suggest that the mining direction should be parallel to the maximum horizontal stress. Overall, the proposed model provides a promising tool for solving 3D complex engineering issues.

Characterization of Silicon Carbon Nitride for Low Temperature Wafer-to-Wafer Direct Bonding

Three-dimensional circuit integration in vertical stacking attracts significant attention as a promising technique to fabricate higher performance and multifunctional chips without current 2D scaling limitation. Generally, the 3D integration using micro bumps consisted of solder joints hold the major integration scheme. However, micro bumps using solders joints confront stacking issues in the case of finer pitch (> 2µm) due to misalignment during thermal compression bonding. The wafer-to-wafer (W2W) hybrid bonding system can be then introduced as one of the state-of-the-art techniques in the 3D integration scheme. In this bonding scheme, two different bonding combinations are established simultaneously, which are Cu-to-Cu and dielectric-to-dielectric, respectively. For these bonding structures, dielectric material adjacent to Cu is required as not only an insulator but also a mechanical factor to withstand the grinding process for further 3D integration. Silicon carbon nitride (SiCN) compound has aroused great interest for bonding dielectrics due to high thermal stability and strong bond strength for direct bonding as well as Cu diffusion barrier ability. Recently back-to-face W2W hybrid bonding using backside SiCN deposition are also challenging to DRAM applications. However, in the case of DRAMs stacking, SiCN W2W direct bonding must be processed at lower temperature (<250°C) due to memory assembly thermal budget although general W2W direct bonding including deposition step of dielectrics is performed at high temperature (>350°C). In the past, we have reported that low temperature bonding using SiCN film deposited at 370°C obtained more than 2.0 J/m2 of adhesion energy at 250°C of post annealing temperature. However, W2W direct bonding using SiCN film deposited at lower temperature (<250°C) have not been studied well. In this study, properties of W2W direct bonding with SiCN deposited at varied temperature are evaluated. Chemical and mechanical properties of SiCN film linked to the bonding quality are fundamentally studied by using specific measurements. The SiCN films were deposited by plasma enhanced chemical vapor deposition (PECVD) at specific temperature 200°C and 370°C. After deposition, these wafers were annealed in a 10% H2/N2 atmosphere at a temperature of 200°C. CMP with typical barrier metal slurry and pad was employed to flatten SiCN surface. Subsequently, the wafer surface was activated by using N2 plasma and rinsed in deionized water. Wafers were finally bonded at room temperature in the EVG GEMINI system. Different characterization techniques have been used to understand the layer quality of the SiCN film deposited at 200°C (which indicated as SiCN 200°C in the text) in comparison with the optimized SiCN deposited at 370°C (indicated as SiCN 370°C). Bond energies for the different wafer pairs have been calculated by using the blade insertion method. The highest bond energy ~ 2.3 J/m2 was obtained in the case of SiCN 370°C, while the bond energy for SiCN 200°C was ~ 1.4 J/m2. ERD observed the elemental composition in bulk for SiCN 370°C and 200°C, respectively (Table 1). It is found that SiCN 200°C is not pure SiCN as SiCN 370°C but it is characterized by the presence of oxygen into the bulk. Oxygen could come from absorbed moisture since deposition and annealing steps are including no oxygen resources. FTIR and XPS were carried out to clarify the chemical components of SiCN 370°C and SiCN 200°C (Figure 1). FTIR spectra of SiCN 200°C is compared with the spectra of SiCN 370°C in Figure 1(a). The broad peak 3100 – 3500cm-1 is assigned to N-H and O-H components, the last one due to moisture absorption from air ambient. A peak at ~1160 cm-1 can be assigned to NH3. This assignment is confirmed through XPS measurements where NH3 peak is detectable in the N1s peak (Figure 1 (c) right) while no NH3 peaks can be detected from the as-deposited SiCN 370°C (Figure 1(b) right). Such observation is suggesting the presence of residue of deposition precursors in the SiCN 200°C. In the Si2p peak of XPS spectra of Figure 1(c), it is observed that SiCN 200°C is characterized by less Si-C bonds compared to the SiCN 370°C as-deposited film. mainly Si-O bonds can be observed in the case of SiCN 200°C after N2 plasma while main peaks didn’t change from CMP for SiCN 370°C (Figure 2). The fact that in the as-deposited SiCN 200°C we do not have Si-C bonds is pointing to a missing desired property for the material since it was demonstrated that Si and C dangling bonds are essential in the process of enhancing bond energies. Figure 1

Heterogeneities at multiple length scales in 2D layered materials: From localized defects and dopants to mesoscopic heterostructures

Two-dimensional (2D) materials hold great promise for applications in optoelectronics, quantum information science, and energy conversion due to their remarkable properties imbued by their physical characteristics. Although heterogeneities in their intrinsic structure are the major challenges limiting their synthesis and predictable properties, they also provide a pathway to controllably tune the properties and broaden the potential of 2D materials. Heterogeneities that can be tailored, including defects, dopants, strain, edges, and layer stackings offer transformative opportunities in heterogeneous 2D materials through the introduction of novel properties for technological applications. This article provides a review of recent progress in studying heterogeneities in 2D materials. The review uses examples from our work to develop a strategy to understand the heterogeneities across multiple length scales to link the effect of heterogeneity at the nanoscale with the macroscale properties of 2D materials. We describe specific types of heterogeneities and explore novel synthesis and processing methods for their controlled production with example of the potential impact and applications enabled by their intriguing properties. Finally, we provide a perspective on how to extend the range of tunable properties through further engineering the heterogeneities in 2D materials.

Deficiency of the scaling collapse as an indicator of a superconductor-insulator quantum phase transition

Finite-size scaling analysis is a well-accepted method for identification and characterization of quantum phase transitions (QPTs) in superconducting, magnetic, and insulating systems. We formally apply this analysis in the form suitable for QPTs in two-dimensional (2D) superconducting films to magnetic-field-driven superconductor-metal transition in one-dimensional (1D) MoGe nanowires. Despite being obviously inapplicable to nanowires, the 2D scaling equation leads to a high-quality scaling collapse of the nanowire resistance in the temperature and resistance ranges comparable or better to what is accepted in the analysis of the films. Our results suggest that the appearance and the quality of the scaling collapse by itself is not a definitive indicator of a QPT. We have also observed a sign change of the zero-bias anomaly (ZBA) in the nonlinear resistance, occurring exactly at the critical field of the accidental QPT. This behavior is often taken as an additional confirmation of the transition. We argue that in nanowires, the nonlinearity is caused by electron heating and has no relation to the critical fluctuations. Our observation suggests that similar to the scaling collapse, the sign change of ZBA can be a misleading indicator of QPT.

Spin memory of the topological material under strong disorder

Robustness to disorder is the defining property of any topological state. The ultimate disorder limits to topological protection are still unknown, although a number of theories predict that even in the amorphous state a quantized conductance might yet reemerge. Here we report that in strongly disordered thin films of the topological material Sb2Te3disorder-induced spin correlations dominate transport of charge—they engender a spin memory phenomenon, generated by the nonequilibrium charge currents controlled by localized spins. We directly detect a glassy yet robust disorder-induced magnetic signal in films free of extrinsic magnetic dopants, which becomes null in a lower-disorder crystalline state. This is where large isotropic negative magnetoresistance (MR)—a hallmark of spin memory—crosses over to positive MR, first with only one e2/h quantum conduction channel, in a weakly antilocalized diffusive transport regime with a 2D scaling characteristic of the topological state. A fresh perspective revealed by our findings is that spin memory effect sets a disorder threshold to the protected topological state. It also points to new possibilities of tuning spin-dependent charge transport by disorder engineering of topological materials.

Error analysis and numerical solution of Burgers–Huxley equation using 3-scale Haar wavelets

In this article, we develop an efficient and accurate numerical scheme based on the Crank–Nicolson finite difference method and Haar wavelet analysis to evaluate the numerical solution of the Burgers–Huxley equation. The present method is extended form of Haar wavelet 2D scaling which shows that it is reliable for solving nonlinear partial differential equations. The numerical results are more accurate than other existing methods available in the literature and very close to the exact solution. The Haar basis function is generated from multi-resolution analysis and used to evaluate fast and accurate approximate solutions on the collocation points. The convergence of the proposed method is demonstrated by its error analysis. We compared numerical solutions with the exact solutions and solutions available in the literature. The proposed method is found to be straight forward, accurate with small computational cost and can be easily implemented in mathematical software MATLAB.

Enabling and Controlling Negative Photoconductance of FePS3 Nanosheets by Hot Carrier Trapping

Abstract2D materials have aroused tremendous attention in the last decade, and magnetic materials of the 2D scale are rising to prominence in recent years, which may revolutionize current optical and electronic applications. Photoconductivity is a well‐known optical and electrical property, which should be positive as the conductivity of material increases typically upon the absorption of electromagnetic radiation. Here, a controllable switch fromnegative to positive photoconductivity effect of FePS3 nanosheets is enabledby the modulation of the excitation wavelengths. These effects originate from an ultrafast process of hot carrier trapping, as visualized and investigated by the transient absorption microscopy at a quantitative level. This hot carrier trapping process is about 1.25 ps resulting in a lower diffusion constant state (≈3.5 cm2 s−1), which provides deep insight into the intrinsic properties of 2D FePS3 for further study. The results demonstrate experimentally the possibility to tune the electronic properties of 2D magnetic materials by an optical way, which not only induces the change in the magnitude but also in the sign, leading to more understandings and possibilities in 2D optoelectronic devices with many unexpected and multifunctional properties.

Recent Advances in Two-Dimensional Magnets: Physics and Devices towards Spintronic Applications.

The emergence of low-dimensional nanomaterials has brought revolutionized development of magnetism, as the size effect can significantly influence the spin arrangement. Since the first demonstration of truly two-dimensional magnetic materials (2DMMs) in 2017, a wide variety of magnetic phases and associated properties have been exhibited in these 2DMMs, which offer a new opportunity to manipulate the spin-based devices efficiently in the future. Herein, we focus on the recent progress of 2DMMs and heterostructures in the aspects of their structural characteristics, physical properties, and spintronic applications. Firstly, the microscopy characterization of the spatial arrangement of spins in 2D lattices is reviewed. Afterwards, the optical probes in the light-matter-spin interactions at the 2D scale are discussed. Then, particularly, we systematically summarize the recent work on the electronic and spintronic devices of 2DMMs. In the section of electronic properties, we raise several exciting phenomena in 2DMMs, i.e., long-distance magnon transport, field-effect transistors, varying magnetoresistance behavior, and (quantum) anomalous Hall effect. In the section of spintronic applications, we highlight spintronic devices based on 2DMMs, e.g., spin valves, spin-orbit torque, spin field-effect transistors, spin tunneling field-effect transistors, and spin-filter magnetic tunnel junctions. At last, we also provide our perspectives on the current challenges and future expectations in this field, which may be a helpful guide for theorists and experimentalists who are exploring the optical, electronic, and spintronic properties of 2DMMs.

On-machine calibration of angular position and runout of a precision rotation stage using two absolute position sensors

A calibration method for a precision rotation stage is proposed to evaluate angular position error and runout of the stage with robustness to alignment error and a simple setup. It consists of two absolute position sensors and a two-dimensional (2D) scale. Therefore, it is proper for on-machine calibration where enough install place and fine adjustment might be unavailable. Angular positions are obtained using two coordinate values on the 2D scale fixed on the rotating plate, and the complete runout is calculated by processing these values through Fourier analysis. The calibrated angular positions of a rotation stage agreed with the reference values within ±1″. The proposed system measured runout with the repeatability of 80 nm and error of 120 nm. An effective compensation method for measurement error caused by out-of-plane motion of the rotation stage was discussed and its feasibility was proved though experiments.

Fluctuation Conductivity and Its Scaling Behavior in BaFe1.9Co0.1As2 Superconductor

Excess fluctuation conductivity of BaFe1.9Co0.1As2 single crystal was studied by measurements of temperature and magnetic field dependence of resistance. The mean field critical temperature Tc (H) is determined by using the criterion of the dR/dT as a function of temperature, where a unique sharp peak appears in the dR/dT curves. By analyzing the excess fluctuation conductivity and the resistance experimental data in the framework of Aslamazov and Larkin theory, different fluctuation regimes such as the three-dimensional (3D), the two-dimensional (2D), the one-dimensional (1D), and short-wave fluctuation (SWF) were identified. In the mean field region, it was also found that the analyses of the resistance experimental data based on the Aslamazov-Larkin theory describes the real measured resistance data very well down to about 0.5 Rn at different regions, which supported the excess fluctuation conductivity results. Based on the lowest Landau level method, both the three-dimensional (3D) and two-dimensional (2D) scaling behaviors were observed in the fluctuation conductivity at magnetic field larger than 5 T and different temperature interval around the mean-field critical temperature Tc.

A Bright Future for Liquid Functional Materials?

Liquid metals were merely sci-fi fantasy a few decades ago, playing a prominent role in the Terminator film franchise. Current research is leading to an array of emerging functional liquids. Here, we discuss the exciting possibilities of such fluid materials.

Design optimization of a non-orthogonal two-axis Lloyd's mirror interferometer for fabrication of large-area two-dimensional scale gratings

An optimized beam expansion assembly is newly designed for a non-orthogonal two-axis Lloyd's mirror interferometer to fabricate large-area two-dimensional (2D) diffraction scale gratings in a small-scale manufacturing facility or a research laboratory. Theoretical calculations are at first carried out to quantitatively estimate the influences of the coherence length and the Gaussian light intensity distribution of a collimated laser beam, which is projected onto a mirror-substrate assembly for the generation of interference fringe fields on a substrate. Design optimization of the interferometer is then carried out in such a way that a beam shaper, which contributes to obtain a flat-top light intensity distribution in the collimated laser beam and is expected to reduce the amplitude deviation of the developed pattern structures as well as the pattern exposure time, is integrated into the beam expansion assembly. The feasibility of the newly developed beam expansion assembly is demonstrated through fabricating a 100 mm × 100 mm 2D scale grating having pattern structures with uniform amplitude of approximately 500 nm and a short period of 1 μm.