Lateral Quantum Research Articles

(Invited) Revolutionizing Data Storage and Brain-Inspired Computing with Perovskite Nanowires and Quantum Wires

Halide perovskites (HPs) have been ubiquitously utilized in optoelectronics and photovoltaics in the recent past owing to their tunable bandgap, long charge diffusion lengths and high color purity. However, their application in resistive random access switching memories (RRAMs) has been somewhat limited by material and electrical instability associated with HP thin-film devices, resulting in below-par figures-of-merits (FOMs) such as data retention time, electrical endurance and switching speed. To collectively address the shortcomings of HP thin-film based RRAMs, we developed a switching matrix which replaces the thin-film anatomy with vertically aligned, three-dimensionally integrated, ultra-high density monocrystalline HP nanowires and quantum wires rooted in a porous alumina membrane (PAM), clubbed between metal contacts acting as the top and bottom electrodes. The PAM provides excellent passivation, providing the required electrical, and material stability to the environmentally delicate HPs by drastically reducing surface diffusion pathways, thereby thwarting moisture-induced attacks.Our approach resulted in record long retention times of up to 28.3 years, measured device endurance of 5 million cycles, and switching speed of 100 ps, the best FOMs ever reported for HP RRAMs. In comparison, the HP thin-film RRAMs exhibited maximum endurance of 10 thousand cycles, best retention of 105 s and best switching speed of 10 ns. Furthermore, we developed a 14 nm lateral size HP quantum wire RRAM cell and a cross-bar device architecture with a unique metal-semiconductor-insulator-metal (MSIM) based sneaky path alleviation scheme that demonstrated the scalability potential of our devices. In addition to data storage, we pioneered the development of HP based neural networks using nanowires and quantum wires in PAM, with low power and high accuracy processing capabilities. Two different modes - electro-chemical metallization (ECM) mode with the silver top electrode and non-electro-chemical metallization (non-ECM) mode with indium tin oxide as top electrode, were used to operate the devices intended for neuromorphic computing application. The obtained multi-level states regulated the modulation of conductance values in the artificial neural networks. They were utilized to perform various image processing tasks such as outlining, sharpening, and embossing in the ECM mode. In the non-ECM mode, we replicated the cognitive learning model of Gestalt Closure Principle by utilizing the multi-level states obtained. Our approach of using HP nanowires and quantum wires embedded in a PAM offers better material reliability, retention, and jitter of the conduction states compared to their thin-film devices. The utilization of HP nanowires and quantum wires in PAM enables the creation of a physical artificial vision system by integrating a physical processor with a physical pre-processor. This integration leads to a consistent photo-synaptic behavior and stable and temporally robust conduction states. The devices demonstrate retention exceeding 105 seconds and temporal jitter less than 10%. They also exhibit photo-synaptic behavior by responding to variations in intensity, duration, and frequency of light pulses, which allows the device to enhance contrast of input visual stimuli. Moreover, we accomplished the recognition of four different geometric shapes using a 6×6 array of nanowire devices, resulting in the creation of a physical artificial vision system that positions HP as a cutting-edge and dependable active layer. This development opens up a multitude of possibilities in the field of artificial intelligence, as it emulates the human vision system.In conclusion, these remarkable advancements propel HP RRAMs to the state-of-the-art standard and highlight the potential of perovskite nanowire/quantum wire devices as a substitute technology for upcoming storage and computing modules.

Lateral Quantum Confinement Effect on High-TC Superconducting FeSe Monolayer.

Despite decades of research in spatially confined superconducting systems to understand the modification of superconductivity from reduced length scales, the investigation of the quantum confinement effect on high-temperature superconductors remains an outstanding challenge. Here, we report scanning tunneling spectroscopy measurements on laterally confined FeSe monolayers on SrTiO3 substrates, which are formed by epitaxially growing FeSe films with a coverage less than one unit cell. Comparing to the uniform regions of FeSe monolayers, the peninsula regions at the monolayer boundary exhibit reduced Fermi energy and undiminished superconductivity, leading to a putative crossover from a Bardeen-Cooper-Schrieffer state to a Bose-Einstein condensate state. In isolated FeSe monolayer islands, superconductivity is shown to exist in samples of smaller volume in contrast to conventional superconductors, while the validity of Anderson's criterion remains fulfilled. Our work reveals lateral quantum confinement effects in unconventional superconductors to enrich the understanding of high-temperature superconductivity in low-dimensional systems.

Evidence of two-dimensional lateral quantum confinement in self-formed core–shell InGaN nanowires on Si (111) emitting in the red

The proof of strong two-dimensional lateral quantum confinement in the In-rich core of red-light emitting self-formed core–shell InGaN nanowires is given. The nanowires are directly grown on Si (111) by plasma-assisted molecular beam epitaxy. After the initial InGaN nucleation, straight nanowires with quantum-size core radius determined by x-ray diffraction, transmission electron microscopy, and energy dispersive x-ray mappings develop. Detailed comparison of the photoluminescence from the core, the In contents of the core and shell, and the core radius with theoretical modeling reveals a parabolic confinement potential with large ground state quantum confinement energies of electrons and holes. Such strong lateral quantum confinement in a vertical quantum wire active region is ideal for the performance of optoelectronic devices, in particular of our reported red InGaN light emitting diode with high brightness and color stability.

Application of lateral flow immunochromatography assay, CRISPR/Cas12, and QDs-based biosensing for SARS-CoV-2 diagnosis

During the COVID-19 pandemic, scientists have developed many diagnostic techniques, such as biosensors, to detect whether a patient is infected by SARS-CoV-2. This could help the governments to plan an effective method to decrease the rate at which the illness is spreading across the globe. These diagnostic techniques are developed after the research of this foreign viral pathogen, SARS-CoV-2, by investigating the potential analytes that could be used and the various ways that the virus could infect a person after exposure. The three diagnostic techniques will be discussed in this paper, including lateral flow immunochromatography assay (LFIA), CRISPR/Cas12, and quantum dots (QDs)-based biosensing system. In addition, this research will also systematically discuss the advantages and disadvantages of these three monitoring and analysis methods. Although these three diagnostic techniques have very high selectivity and sensitivity, establishing a reliable result, there are pathogens that could result in similar symptoms of respiratory pneumonia just like SARS-CoV-2. The diagnostic techniques explained in this paper cant diagnose more than one pathogen or disease, therefore, it is essential to further develop a multiplexing assay to produce a more detailed result.

Edge Conductivity in PtSe2 Nanostructures

PtSe2 is a promising 2D material for nanoelectromechanical sensing and photodetection in the infrared regime. One of its most compelling features is the facile synthesis at temperatures below 500 °C, which is compatible with current back‐end‐of‐line semiconductor processing. However, this process generates polycrystalline thin films with nanoflake‐like domains of 5–100 nm size. To investigate the lateral quantum confinement effect in this size regime, a deep neural network is trained to obtain an interatomic potential at density functional theory accuracy and it is used to model ribbons, surfaces, nanoflakes, and nanoplatelets of PtSe2 with lateral widths between 5 and 15 nm. Which edge terminations are the most stable are determined and evidence is found that the electrical conductivity is localized on the edges for lateral sizes below 10 nm. This suggests that the transport channels in thin films of PtSe2 might be dominated by networks of edges, instead of transport through the layers themselves.

Theoretical study of electron compressibility in semiconductor quantum wires

The compressibility was calculated of electrons as a function of external magnetic, temperature and carrier density in the parabolic lateral barrier quantum wires (QWRs). The compressibility found by using Seitz's theorem in which electron self-energy is calculated within the random-phase approximation. All results for GaAs QWRs show that a large difference between the compressibility in low- and high-temperature region at external magnetic fields. These results can help clarify how the Coulomb interaction and exchange, correlation energy affect the compressibility of the semiconductor across a wide range of density, temperature, and external magnetic.

Production of Magnetic Arsenic-Phosphorus Alloy Nanoribbons with Small Band Gaps and High Hole Conductivities.

Quasi-1D nanoribbons provide a unique route to diversifying the properties of their parent 2D nanomaterial, introducing lateral quantum confinement and an abundance of edge sites. Here, a new family of nanomaterials is opened with the creation of arsenic-phosphorus alloy nanoribbons (AsPNRs). By ionically etching the layered crystal black arsenic-phosphorus using lithium electride followed by dissolution in amidic solvents, solutions of AsPNRs are formed. The ribbons are typically few-layered, several micrometers long with widths tens of nanometers across, and both highly flexible and crystalline. The AsPNRs are highly electrically conducting above 130 K due to their small band gap (ca. 0.035 eV), paramagnetic in nature, and have high hole mobilities, as measured with the first generation of AsP devices, directly highlighting their properties and utility in electronic devices such as near-infrared detectors, quantum computing, and charge carrier layers in solar cells.

Nanoscale patterning on layered MoS2 with stacking-dependent morphologies and optical tunning for phototransistor applications

Nanoscale patterning has attracted considerable interest as a novel engineering technology for two-dimensional (2D) nanomaterials for various applications such as electronics, sensors, and catalysts. However, research on nanopatterning technologies that reflect the unique structural and electrical characteristics of 2D nanomaterials remains insufficient. In this study, we present a nanoscale patterning of two different polygons on layered molybdenum disulfide (MoS2), where the nanostructures are controlled by the stacking structure of MoS2. We investigate the dependence of nanopore edge stability on the stacking structure of MoS2 using density functional theory calculations and find the different geometric effects of the two nanopatterns on the band-structure modulation of semiconducting MoS2. Consistent with the theoretical calculations, we fabricate nanoporous MoS2 with hexagonal nanopores for AA’ and triangular nanopores for AB stacked MoS2 films. The AA’ MoS2 has narrow nanoribbons between the two hexagonal nanopores, resulting in a lateral quantum confinement effect, whereas the edge exposure effect is more dominant for the bandgap increase in the triangular nanoporous structure. Nanopatterns contribute to generating in-gap state of MoS2, significantly enhancing the photoelectrical characteristics of MoS2 phototransistors. Especially, the photogating effect is higher for AA’ MoS2 phototransistors with hexagonal nanoholes than AB MoS2 with triangular nanoholes. This study provides new insights into nanoscale patterning and band structure engineering of layered 2D materials for various optoelectrical applications.

Optical Tunable Moiré Excitons in Twisted Hexagonal GaTe Bilayers

Optical fine-tunable layer-hybridized Moiré excitons are highly in demand for emerging many-body states in two-dimensional semiconductors. We report naturally confined layer-hybridized bright Moiré excitons with long lifetimes in twisted hexagonal GaTe bilayers, using ab initio many-body perturbation theory and the Bethe–Salpeter equation. Due to the hybridization of electrons and holes between layers, which enhances the brightness of excitons, the twisted bilayer system becomes attractive for optical applications. We find that in both R and H-type stacking Moiré superlattices, more than 200 meV lateral quantum confinements occur on exciton energies, which results in two scenarios: (1) The ground state bright excitons XA are found to be trapped at two high-symmetry points, with opposite electric dipoles in the R-stacking Moiré supercell, forming a honeycomb superlattice of nearest-neighbor dipolar attraction. (2) For H-stacking case, the XA is found to be trapped at only one high-symmetry point exhibiting a triangular superlattice. Our results suggest that twisted h-GaTe bilayer is one of the promising systems for optical fine-tunable excitonic devices and provide an ideal platform for realizing strong correlated Bose–Hubbard physics.

A graphene-nanoribbon-based thermoelectric generator

Unlike graphene flakes which are semi-metallic with zero bandgaps, graphene nanoribbons (GNRs) are semiconductors with a sizeable bandgap generated by lateral quantum confinement. In this work, semiconducting GNRs are synthesized to fabricate thermoelectric generators (TEGs), which have been envisaged theoretically but are yet to be demonstrated experimentally to date. The GNRs are produced by unzipping single-walled carbon nanotubes through a mild chemical rection and ultrasonic process in solution. The semiconducting nature of the GNRs is demonstrated by strong, sharp emission of photoluminescence at 685 nm, corresponding to a bandgap of 1.81 eV, and further confirmed by on/off ratios up to 400 in the GNR-based field-effect transistors. The GNR TEGs exhibit a high Seebeck coefficient of 68 μVK−1 and a power factor of 6.76 μWm−1K−2 at room temperature, which are amongst the best in carbon-based thermoelectric devices. Finally, tests also demonstrate that the GNR TEGs are mechanically robust and flexible, showing promise in thermoelectric applications for flexible electronics.

Lateral quantum confinement regulates charge carrier transfer and biexciton interaction in CdSe/CdSeS core/crown nanoplatelets

Charge carrier dynamics essentially determine the performance of various optoelectronic applications of colloidal semiconductor nanocrystals. Among them, two-dimensional nanoplatelets provide new adjustment freedom for their unique core/crown heterostructure. Herein, we demonstrate that by fine-tuning the core size and the lateral quantum confinement, the charge carrier transfer rate from the crown to the core can be varied by one order of magnitude in CdSe/CdSeS core/alloy-crown nanoplatelets. In addition, the transfer can be affected by a carrier blocking mechanism, i.e., the filled carriers hinder further possible transfer. Furthermore, we found that the biexciton interaction is oppositely affected by quantum confinement and electron delocalization, resulting in a non-monotonic variation of the biexciton binding energy with the emission wavelength. This work provides new observations and insights into the charge carrier transfer dynamics and exciton interactions in colloidal nanoplatelets and will promote their further applications in lasing, display, sensing, etc.

Magnetization Of A Quantum Dot Superlattice System In The Presence Of A Rashba Spin-Orbit Coupling Term

In this paper, we have investigated the magnetization and the magnetic susceptibility of a quantum dot superlattice system in the presence of a magnetic field parallel to the superlattice axis and confined in a lateral parabolic quantum well. We took the effect of the Rashba spin-orbit interaction and Zeeman term on the specific heat into account. We have calculated the energy spectrum of the electron in the quantum dot superlattice system. Moreover, we have calculated the magnetization and the magnetic susceptibility dependence on the magnetic field and temperature of a quantum dot superlattice system.

Optical absorption of conduction electrons in semiconductor nanowires in the presence of the electron–phonon interaction

We calculate the energy states and the optical absorption coefficient for electrons in a nanowire in the presence of the Rashba and the longitudinal-optical phonon interactions. The interplay of those interactions results in a splitting in the electron dispersion relation at zero wavevector that grows linearly for the ground state as the strength of the lateral quantum confinement increases. For higher states, the energy splitting increases more rapidly till the state of resonant polaron is reached, then it increases slowly due to the pinning effect. The frequency separation between the well-resolved absorption peaks and their number are greatly influenced by the state of the polarons.

(Digital Presentation) Resistive Switching and Brain-Inspired Computing in Perovskite Nanowires and Quantum Wires

In the past decade, halide perovskites (HPs) have shot to fame in the genre of optoelectronics and photovoltaics owing to their large absorption co-effcient, high color purity, tunable bandgap and long charge diffusion lengths. Besides these traits, HPs also possess innumerable charge transport pathways, inherent hysteresis, high charge-carrier and ionic mobilities which render them as ideal candidates for resistive random access switching memories (RRAMs). However owing to material and electrical instability associated with HP thin-film devices, the figures-of-merits (FOMs) namely retention, endurance and switching speed were not up to the state of-the-art standard until recently. In order to revolutionize HP Re-RAMs we devised a unique device structure where we replaced the thin-film architecture with vertically aligned high density HP nanowires and quantum wires embedded in a porous alumina membrane (PAM) sandwiched between metallic silver and aluminum contacts. The excellent passivation provided by the PAM imparted the requisite electrical and material stability to the environmentally delicate HPs by drastically reducing the surface diffusion pathways and thereby thwarting the moisture induced attacks. Extrapolated retention time as high as 28.3 years and measured device endurance of a million cycles were obtained. Utilizing the single crystalline HP nanowires and quantum wires and their associated high ionic and electronic mobilities, switching speed as fast as 100 ps was also obtained. These FOMs represent record values for HP RRAMs ever reported. Furthermore a 14 nm lateral size HP quantum wire RRAM cell was fabricated and a cross-bar device architecture with a unique sneaky path mitigation scheme were developed, which successfully exhibited the scalability potential of our devices. We further coupled the optoelectronic and switching behaviors and were able to obtain optical programmability among the low resistance states. Besides data storage, the HP nanowires and quantum wires were employed in developing neuromorphic devices enabled with low power and high precision computing capabilities. Specifically, we obtained robust multi-level states in two types of brain-inspired devices capable of performing analog processing tasks by using silver as the top electrode and precisely controlling the current injection in the monocrytalline switching medium and by using indium doped tin oxide as the top electrode and inducing a novel valence change mechanism in the HP nanowires triggering the gradual conductance change. All in all, our nanowire and quantum wire devices propel HP RRAMs to the state-of-the-art standard in multifarious applications concerning future data storage and neuromorphic computing.

Weighted Full-Focus Defect Detection and Imaging Method Based on Threshold Fusion for Phase Coherence Factor

Total focus (TFM) ultrasonic inspection imaging only uses the amplitude of defect data for delayed stack imaging (DAS), ignoring the phase information in the echo signal, which easily leads to low imaging resolution and interferes with subsequent quantitative analysis of defect size. To solve these problems, this paper proposes a phase coherence factor (TF-PCF) weighted full-focus imaging method based on threshold fusion: by combining the image sound intensity matrix with mathematical statistics, a reasonable threshold is set to screen out the effective pixels, and the parameter selection rules of the PCI algorithm model are redefined. The simulation and experimental results show that the TF-PCF imaging algorithm can effectively eliminate the noise information in the imaging area, including the artifacts near the defects that are difficult to be processed by PCI. Compared with PCI, TF-PCF has higher ability to quantify defect size. When using p-wave to detect large objects with a large number of defects and complex location distribution, the lateral size quantization error of the TF-PCF imaging algorithm is reduced by 8.5%. When sampling shear wave imaging to detect defects with tilted wedges, the lateral and longitudinal size quantization errors of defects are reduced by 10% and 20%, respectively. The reliability of defect size quantitative analysis is improved. Under the same test conditions, the complexity of TF-PCF model is far less than that of PCI model, which greatly improves the practicability of the algorithm model.

Strain Release Enabled Bandgap Scaling in Ge Nanowire and Tunnel FET Application

The cross-sectional scaling-induced electronic property variations of the Ge and Si nanowires are studied numerically. After removing extra atoms from bulk materials to build the nanowires, not only the lateral quantum confinement is enhanced, but also the cross-sectional size will expand due to the breaking of the intrinsic strain balance. Compared with Si, the strain release-induced size expansion is more obvious in the Ge nanowires, shrinking the bandgaps and thus providing another bandgap modulation direction relative to the quantum confinement. At specific sizes, the strain release effect dominates the modulation and reduces the bandgaps of Ge nanowires even below the bulk value, while the reductions in Si nanowires are negligible, enlarging the band offsets of their heterostructures. As an application, the Ge/Si heterostructure tunnel FET (TFET) is designed and the TCAD simulation reveals a subthreshold swing (SS) of 13.8 mV/dec and an ON-state current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$93 ~\mu \text{A}/\mu \text{m}$ </tex-math></inline-formula> , three orders of magnitude larger than that using the bulk materials.

The Gaussian impurity effect on the electronic and magnetic properties of an electron confined in a lateral quantum dot

The Gaussian impurity effect on the electronic and magnetic properties of an electron confined in a lateral quantum dot

Effective Optical Properties of Laterally Coalescing Monolayer MoS2.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) exhibit compelling dimension-dependent exciton-dominated optical behavior influenced by thickness and lateral quantum confinement effects. Thickness quantum confinement effects have been observed; however, experimental optical property assessment of nanoscale lateral dimension monolayer TMDCs is lacking. Here, we employ ex situ spectroscopic ellipsometry to evaluate laterally coalescing monolayer metalorganic chemical vapor deposited MoS2. A multisample analysis is used to constrain Bruggeman and Maxwell-Garnett effective medium approximations and the effective dielectric functions are derived for laterally coalesced and uncoalesced MoS2 films (∼10-94% surface coverage for ∼10-140 nm lateral grain sizes). This analysis demonstrates the ability to probe MoS2 optical exciton behavior at growth-relevant grain sizes in relation to chemical vapor nucleation density, ripening, and lateral growth conditions. Our analysis is pertinent toward expected in situ epitaxial 2D TMDC film growth metrology to enable the facile development of monolayer films with targeted process-dependent optical properties.

Water-Phase Lateral Interconnecting Quantum Dots as Free-Floating 2D Film Assembled by Hydrogen-Bonding Interactions to Acquire Excellent Electrocatalytic Activity.

Supramolecular self-assembly of nanoparticles in two orthogonal directions would potentially allow one to fabricate nanomaterials with fascinating properties. In this study of a hydrothermal polycondensation of melamine/cyanuric acid, graphitic carbon nitride-based quantum dots (CNQD, ∼2 nm) are in situ arranged along two orthogonal directions through lateral hydrogen bonding, and free-floating two-dimensional hydrogen-bonded films of CNQD (2D CNQD) are built. On the basis of the universality of this hydrothermal in situ supramolecular self-assembly technique, 2D films linked by other quantum dots such as sulfur-doped graphitic carbon nitride and CdTe are also constructed. With the benefits of stimuli responsiveness and the reversibility of hydrogen bonds, controllable assembly/disassembly of the 2D CNQD film is feasibly achieved by external stimuli such as inletting CO2/N2, which endows the assembled 2D CNQD films optimal electrochemical superiorities of both 2D film and zero-dimensional (0D) quantum dots. Accordingly, the 2D CNQD film delivers a high bifunctional activity in both a nitrogen reduction reaction (NRR) and an oxygen evolution reaction (OER). Especially in NRR, it exhibits the high yield rate of NH3 reaching 75.07 μg h-1 mg-1 at -0.85 V versus reversible hydrogen electrode at ambient condition. Strikingly, the power density of the rechargeable Zn-N2 battery using 2D CNQD film as cathode reaches 31.94 mW cm-2, outperforming the majority of Zn-N2 batteries. Density functional theory calculations proved the promoted adsorption of N2 and stabilized NRR intermediates on 2D CNQD cooperated by multiply hydrogen-bonding interactions are the main reasons for the excellent NRR electrocatalytic performances. This work hints that hydrothermal in situ supramolecular self-assembly is a feasible and direct way to integrate 0D quantum dots into 2D directional arrays, and the hydrogen bond that interlinks enables this free-floating 2D structure to maintain the electrochemical superiority of both 0D and 2D structures.

Changing Spin and Orbital Ground State Symmetries in Colloidal Nanoplatelets with Magnetic Fields

The symmetry of the electronic ground state is of paramount importance in determining the magnetic, optical and electrical properties of semiconductor nanostructures. Here it is shown theoretically that non-trivial spin and orbital symmetries can be induced in colloidal nanoplatelets by applying out-of-plane magnetic fields. Two scenarios are presented. The first one deals with two electrons confined inside a platelet. Here, the strong electron-electron exchange interaction reduces the interlevel energy spacing set by lateral quantum confinement. As a result, relatively weak magnetic fields suffice to induce a singlet-to-triplet spin transition. The second one deals with type-II core/crown nanoplatelets. Here, the crown has doubly-connected topology, akin to that of quantum rings. As a result, the energy levels of carriers within it undergo Aharonov-Bohm oscillations. This implies changes in the ground state orbital symmetry, which switch the exciton and trion optical activity from bright to dark.This article is protected by copyright. All rights reserved.