Nanotechnology最新文献

Quasi-two-dimensional nanosheets exhibit novel properties and promising applications in optoelectronic flexible devices. Research on non-layered III-V semiconductor nanosheets has been constrained by their covalent bonding connections. In this study, GaAs/AlGaAs heterojunction nanosheets were prepared by releasing an epitaxial layer, and their optical properties were investigated by adopting steady-state and transient absorption spectroscopy. The optical properties of the independent GaAs/AlGaAs heterojunction were investigated separately in order to exclude the effect of the substrate. This work provides a comprehensive understanding of the physics of III-V semiconductor quasi-two-dimensional nanosheets.

The growing world population and climate change are key drivers for the increasing pursuit of more efficient and environmentally-safe food production. In this scenario, the large scale use of herbicides demands the development of new technologies to control and monitor the application of these compounds, due to their severe environmental and health-related problems. Motivated by these issues, in this work, a hybrid graphene/boron nitride nanopore is explored to detect/identify herbicide molecules (Glyphosate, aminomethylphosphonic acid, Diuron, and 2,4D). Solid-state nanopores based on 2D materials have been widely explored as novel generation sensors capable of single-molecule resolution. The present investigation combines density functional theory (DFT) and the non-equilibrium Green's function method to assess the interaction of each herbicide with the nanopore and how its interaction modulates the device's electronic transport properties. The device's sensitivity spreads from 9.0% up to 27.0% when probed at different gate voltages. Overall, the proposed device seems to be sensitive and selective to be considered as a promising single-molecule herbicide sensor.

The utilization of two-working-electrode mode of interdigitated array (IDA) electrodes and other two-electrode systems has revolutionized electrochemical detection by enabling the simultaneous and independent detection of two species or reactions. In contrast to conventional two-potential electrodes, such as the rotating ring disk electrodes, IDAs demonstrate analogous yet vastly improved performance, characterized by remarkable collection efficiency, sensitivity, and signal amplification resulted from the 'feedback' effect. In recent decades, the research surrounding IDAs has garnered escalating interest due to their attractive attributes. This review centers its focus on the recent development on the fabrication of IDA electrodes as well as their applications leveraging the unique electrochemical and structural features. In fabrication, two critical breakthroughs are poised for realization: the achievement of reduced dimensions and the diversification of materials. Established fabrication methods for IDA electrodes encompass photolithography, inkjet printing, and direct laser writing, each affording distinct advantages in terms of size and precision. Photolithography enables the creation with finer structures and higher resolution compared to others. Inkjet printing or laser writing provides a simpler, more cost-effective, and straightforward patterning process, albeit with lower resolution. In terms of applications, IDAs have found utility in diverse fields. This review summarizes recent applications based on their fundamental working principles, encompassing redox cycling, resistance modulation, capacitance variations, and more. This specialized tool shows great promise for further development with enhanced properties. It is also important to note that, micron- or sub-micron-sized IDAs generally cannot be reused, as their small structures cannot be polished. Therefore, controlling the cost of IDA fabrication is crucial for promoting their broader application. Additionally, the distinctive electrochemical properties of 'feedback' effect is often underappreciated. The high sensitivity of IDA electrodes, arising from the 'feedback' signal amplification mechanism, holds significant potential for the detection of species with short lifetimes or low concentrations.

We investigate the effect of focused-ion-beam (FIB) irradiation on spin waves with sub-micron wavelengths in yttrium-iron-garnet films. Time-resolved scanning transmission x-ray microscopy was used to image the spin waves in irradiated regions and deduce corresponding changes in the magnetic parameters of the film. We find that the changes of Ga⁺irradiation can be understood by assuming a few percent change in the effective magnetizationMeffof the film due to a trade-off between changes in anisotropy and effective film thickness. Our results demonstrate that FIB irradiation can be used to locally alter the dispersion relation and the effective refractive indexneffof the film, even for submicron wavelengths. To achieve the same change innefffor shorter wavelengths, a higher dose is required, but no significant deterioration of spin wave propagation length in the irradiated regions was observed, even at the highest applied doses.

Lead-free cesium bismuth iodide (Cs₃Bi₂I₉) perovskite exhibits extraordinary optoelectronic properties and attractive potential in various optoelectronic devices, especially the application for photodetectors (PDs). However, most Cs₃Bi₂I₉PDs demonstrated poor detection performance due to the difficulty in obtaining high-quality polycrystalline films. Therefore, it makes sense to modulate the preparation of high-quality Cs₃Bi₂I₉polycrystalline films and expand its applications. Here, a solvent-modulated method combining anti-solvent and precursor engineering has been developed to regulate the crystallization dynamics of Cs₃Bi₂I₉. Anti-solvent treatment is to suppress the asynchronous separation out of CsI and BiI₃due to significant differences in solubility, promoting uniform nucleation and limiting flake-like growth. Precursor engineering is synchronously used to modulate the subsequent nucleation growth dynamics. Due to the synergistic modulation, smooth and compact Cs₃Bi₂I₉polycrystalline films with distinct grains and grain boundaries can be easily obtained. The as-prepared PD exhibits an excellent on/off ratio of 4.26 × 10⁵as well as the detectivity up to 6.49 × 10¹⁰Jones at zero bias. And, the Cs₃Bi₂I₉PD indicates excellent device stability, maintaining about 70% of the original performance after being stored for 400 h in the air without encapsulation.

Developing a reliable procedure for the growth of III-V nanowires (NW) on silicon (Si) substrates remains a significant challenge, as current methods rely on trial-and-error approaches with varying interpretations of critical process steps such as sample preparation, Au-Si alloy formation in the growth reactor, and NW alignment. Addressing these challenges is essential for enabling high-performance electronic and optoelectronic devices that combine the superior properties of III-V NW semiconductors with the well-established Si-based technology. Combining conventional scalable growth methods, such as metalorganic chemical vapor deposition (MOCVD) within situcharacterization using environmental transmission electron microscopy (ETEM-MOCVD) enables a deeper understanding of the growth dynamics, if that knowledge is transferable to the scalable processes. We report on successful epitaxial growth of Au-catalyzed GaAs NWs on Si(111) substrates using micro-electromechanical system chips with monocrystalline Si-cantilevers in both conventional MOCVD and ETEM-MOCVD systems. The conventional MOCVD provided a framework for initial parameter tuning, while ETEM-MOCVD offered valuable insights into early nucleation and catalyst-substrate interactions. Our findings show that nucleation is significantly influenced by the removal of native oxide layers and the initial formation of the Au-Si alloy. Ourin situstudies revealed different NW-substrate interfaces, essential for optimizing the epitaxial growth process. We identified three typical configurations of NW 'roots', each impacted by growth conditions and preparation steps, affecting the structural and potentially the optical properties of the NWs. Similarly, doping from the Si-substrate may affect both optical and electrical properties; however, compositional analysis revealed no traces of Si in NWs post-nucleation and a small amount in the catalytic droplet. Our research highlights the importance ofin situstudies for a comprehensive understanding of nucleation mechanisms, paving the way for optimizing III-V NW growth on Si substrates and developing high-performance III-V/Si devices.

Both stability and multi-level switching are crucial performance aspects for resistive random-access memory (RRAM), each playing a significant role in improving overall device performance. In this study, we successfully integrate these two features into a single RRAM configuration by embedding Ag-nanoparticles (Ag-NPs) into the TiN/Ta₂O₅/ITO structure. The device exhibits substantially lower switching voltages, a larger switching ratio, and multi-level switching phenomena compared to many other nanoparticle-embedded devices. We attribute it to the embedded Ag-NPs effectively switching the mechanism of conductive filaments and the controlled distribution of Ag-NPs facilitates the occurrence of multi-level switching. Additionally, the fabricated structure demonstrated an impressive optical transmittance of nearly 85%. Undoubtedly, this combined feature of RRAM not only enhances stability but also enables multi-level switching, thereby demonstrating an approach to fabricating versatile and practical electronic devices aimed at boosting storage capacity and speed.

Structural and photoelectric properties of p-i-n photodiodes based on GeSiSn/Si multiple quantum dots (QDs) both on Si and silicon-on-insulator substrates were investigated. Elastic strained state of grown films was demonstrated by x-ray diffractometry. Annealing of p-i-n structures before the mesa fabrication can improve the ideality factor of current-voltage characteristics. The lowest dark current density of p-i-n photodiodes based on QDs at the reverse bias of 1 V reaches the value of 0.8 mA cm^-2. The cutoff wavelength shifts to the long-wavelength region with the Sn content increase. Maximum cutoff wavelength value is found to be 2.6μm. Moreover, multilayer periodic structures with GeSiSn/Ge quantum wells and GeSiSn relaxed layers on Ge substrates were obtained. Reciprocal space maps were used to study the strained state of GeSiSn layers. The optimal growth parameters were determined to obtain slightly relaxed GeSiSn layers. Designed p-i-n photodiodes based on these structures demonstrated the minimal dark current density of 0.7 mA cm^-2and the cutoff wavelength of about 2μm.

Non-equilibrium molecular dynamics simulations reveal the existence of a spontaneous heat current (SHC) in the absence of a temperature gradient and demonstrate ultra-high thermal rectification in asymmetric trapezoid-shaped graphene. These unique properties have potential applications in power generation and thermal circuits, functioning as thermal diodes. Our findings also show the presence of negative and zero thermal conductivity in this system. The negative thermal conductivity could enable the design of a conductive heat machine that pumps heat from the cold side to the hot side without additional energy consumption, functioning as a 'full-free refrigerator'. Meanwhile, zero thermal conductivity paves the way for the development of high-efficiency thermoelectric devices. Simulations were performed in two scenarios: with hydrogenated edges and without them. To ensure the reliability of the results, Reactive Empirical Bond Order and Tersoff potentials were employed. Finally, we examined how the SHC and the temperature difference at which the heat current is zero depend on the sample length, system width, and system temperature.

Decoration of TiO2 nanotube (TNT) arrays by AuPd nanoparticles (NPs) produces a dramatic enhancement in the rate of hydrogen generation through photocatalytic water-splitting under solar illumination. XRD and TEM confirmed alloy formation in bimetallic AuPd NPs while XPS ruled out a core-shell architecture in the AuPd NPs. Well-dispersed, size-controlled AuPd NPs were formed by sequential physical vapor deposition of Au and Pd on TNTs followed by spontaneous thermal dewetting (TNT-AuPd). TNT-AuPd samples were characterized by small tensile microstrains. For comparison purposes and to derive physical insights, an identical method was used to form TNT-Au and TNT-Pd samples wherein TNTs were decorated by monometallic Au and Pd NPs respectively. In every case, an accumulation-type heterointerface between TiO2 and the metallic/bimetallic NPs was indicated by binding energy shifts in the Ti2p high resolution x-ray photoelectron spectra (HR-XPS). Initial and final state effects in the Au4f HR-XPS pointed to a large number of Au atoms in low coordinate sites such as edges, kinks and corners as well as a slower excited atom relaxation in the alloy. A similar preponderance of Pd atoms at low coordinate sites was found along with the presence of a small amount of palladium oxide. TNT-AuPd demonstrated the highest photocatalytic H₂ production rate of 2920 µmol g⁻¹ h⁻¹, which is 8.9 times higher than that of TNTs, 2.1 times that of TNT-Au, and 1.69 times that of TNT-Pd under solar illumination. We studied H₂ generation under UV-filtered solar illumination with TNT-AuPd outperforming monometallic Au- and Pd-NP decorated TNTs, which is attributed to the enhancement of the catalytic activity of Pd in an Au environment, the presence of Pd and Au atoms at low coordinate sites, and photoinduced electron transfer between TNTs and AuPd alloy NPs, where AuPd acts as an efficient electron sink, in turn reducing carrier recombination losses.