Nanotechnology最新文献

We investigate the electronic properties of nanoribbons made out of monolayer Lieb, transition, and kagome lattices using the tight-binding model with a generic Hamiltonian. It allows us to map the evolutionary stages of the interconvertibility process between Lieb and kagome nanoribbons by means of only one control parameter. Results for the energy spectra, the density of states, and spatial probability density distributions are discussed for nanoribbons with three types of edges: straight, bearded, and asymmetric. We explore for different nanoribbon terminations: (i) the semiconductor-metallic transition due to the interconvertibility of the Lieb and kagome lattices, (ii) the effect of both nanoribbon width and inclusion of the next-nearest-neighbor hopping term on the degeneracy of the quasi-flat states, (iii) the behavior of the energy gap versus the nanoribbon width, (iv) the existence and evolution of edge states, and (v) the nodal spatial distributions of the total probability densities of the non-dispersive states.

In this work, a novel composite anode material was developed, utilizing S-doped graphene oxide (SGO), polypyrrole (PPy), and fumed silica to enhance the performance of lithium-ion batteries (LIBs). The chronoamperometric approach was used to produce SGO, while the chemical method was employed to synthesize PPy. A composite of SGO, PPy, and fumed silica was prepared as an anode for a half-cell, using two samples: one with a high PPy ratio (S1) and the other with a low PPy ratio (S2) and compared the results with bare sample (S0). The S1 sample exhibited a good initial discharge capacity (648 mAh g^-1), with capacities of 207 and 131 mAh g^-1at 5 C and 10 C, respectively. S1 and S2 also demonstrated superior cycling stability at a high current (100 cycles at 10 C), with a retention capacity of 99 and 87%, respectively compared with S0 which retained only 68%. Coin-type full cells with S1 as the anode and LiFePO₄(LFP) as the cathode were assembled and compared with commercial graphite anodes. The S1 full cell showed a high reversible capacity (164 mAh g^-1at 0.1 C), with a capacity retention of 66% after 100 cycles at 10 C. At the same time, the graphite anode exhibited a reversible capacity of 133 mAh g^-1at 0.1 C, with a capacity retention of 58% after 100 cycles at 10 C. The S1 full cell achieved a gravimetric energy density of 164 W h kg^-1at 0.1 C and 49 W h kg^-1at 10 C, which is 25% greater than that of the graphite full cell(39 W h kg^-1) at 10 C. These distinguishing characteristics of S1 make it a viable substitute for graphite as a high-performance anode material in LIBs, opening the possibility for devices with reliable battery systems.

The present work describes the synthesis of WO₃-BiVO₄-nanoflakes heterostructure (NFHs) by a single step hydrothermal method. The analysis of crystalline phases and structural behavior deduced the formation of good crystal quality WO₃-BiVO₄NFHs. Under microscopic observation, the as-prepared WO₃-BiVO₄displayed uniform and conspicuous nanoflakes like structures. The extensive density functional theory was studied to examine the electronic and band structures of as-prepared WO₃-BiVO₄NFHs in terms of formation energy, charge density, density of state and band structures. The synthesized WO₃-BiVO₄NFHs was used as sensing electrode towards the detection of ethylenediamine (EDA) chemical that displayed a good sensitivity of ∼318.52 mA·mM^-1cm^-2, excellent dynamic range of 1μM-1 mM with detection limit of ∼94.51 nM and retention coefficient of ∼0.9929. WO₃-BiVO₄NFHs electrode possessed the good reproducibility, stability, and repeatability towards EDA chemical. To the best of our knowledge, for the first time, the fabricated chemical sensor fabricated with WO₃-BiVO₄NFHs electrode could be promising electrode materials to identify dangerous chemicals at very low concentration in environment. Importantly, the fabricated chemical sensor can be effective for environmental monitoring.

Surface-induced crystallization/amorphization of a Germanium-antimony-tellurium nanolayer is investigated using the phase field model. A Ginzburg-Landau (GL) equation introduces an external surface layer (ESL) within which the surface energy and elastic properties are adequately distributed. Next, the coupled GL and elasticity equations for the crystallization/ amorphization are solved. For the initial surface crystalline nucleus, unphysical crystallization along the ESL appears for the ESL widthΔξ⩾2nmwhile oval growth occurs forΔξ⩽1nm. The ESL results in a faster surface nucleus growth than the sharp surface model but does not affect the crystallization rate inside the bulk. Initial homogeneous conditions cause a simultaneous crystallization in the bulk and later in the ESL. The ESL effect on amorphization is studied to determine the ESL width more precisely. For both the initial amorphous nucleus and homogenous conditions, the amorphization temperature shows a reduction from the sharp surface model to the ESL model withΔξ=0.5nmand then remains almost constant for largerΔξ. Combining the above results gives0.5⩽Δξ⩽1nmas a proper range for the ESL width. The ratio of the effective ESL width to the interface width (Δsat/Δη) and the ratio of the difference between the surface energies of transforming phases to the surface energy of the initial phase (Δγ/γin) are considered crucial parameters in determining the ESL effect on the phase transformation and a linear relation asΔsat/Δη≅6.235Δγ/γinis found based on current and previous works, which can help estimate the effective ESL width for any surface-induced transformations.

Non-equilibrium molecular dynamics (NEMD) 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.

Structural and photoelectric properties of p-i-n photodiodes based on GeSiSn/Si multiple quantum dots both on Si and silicon-on-insulator (SOI) 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 quantum dots at the reverse bias of 1 V reaches the value of 0.8 mA/cm2. The cutoff wavelength shifts to the long-wavelength region with the Sn content increase. Maximum cutoff wavelength value is found to be 2.6 μm. 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/cm2 and the cutoff wavelength of about 2 μm.

Color centers are promising single-photon emitters owing to their operation at room temperature and high photostability. In particular, using nanodiamonds as a host material is of interest for sensing and metrology. Furthermore, being a solid-state system allows for incorporation to photonic systems to tune both the emission intensity and photoluminescence spectrum and therefore adapt the individual color center to desired properties. We show successful coupling of a single nanodiamond hosting silicon-vacancy color centers to a plasmonic double bowtie antenna structure. To predict the spectrum of the coupled system, the photoluminescence spectrum of the SiV centers was measured before the coupling process and convoluted with the antenna resonance spectrum. After transferring the nanodiamond to the antenna the combined spectrum was measured again. The measurement agrees well with the calculated prediction of the coupled system and therefore confirms successful coupling.

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. .

Supercapacitors are energy storage devices with long cycle life that can harvest and deliver high power. This makes them attractive for a broad range of applications including flexible and lightweight wearable consumer electronics. In this work, we fabricate flexible solid-state supercapacitors with improved capacitance and cycle life. We synthesize activated carbon (AC) from cabbage leaves as a low cost, biowaste-derived active electrode material. To improve mechanical flexibility and conductivity, we incorporate reduced graphene oxide sheets (RGO) and carbon quantum dots (CQDs) into the electrodes. We show that at the optimum AC/RGO/CQD composition, the capacitance of the solid-state supercapacitor is maximized while its scan rate dependence and bending stability are simultaneously improved. We envision that this approach offers significant potential for delivering efficient energy storage devices for consumer electronics.

The performance of silver nanowire (AgNW) network flexible transparent electrodes is limited by large contact resistance, making it necessary to perform nanowelding to improve conductivity of the network. However, not all nanowire junctions can be welded. Our work indicates that the welding kinetics between nanowires depend on the crossing angle, with higher surface diffusion velocity prone to welding and fracture at nanowire junctions of crossing angles close to 90 degrees. The impact of nanowire crossing angles on the welding process makes it difficult to achieve simultaneous welding of random AgNWs networks. To address this issue, we adopted an improved Meyer rod coating method to prepared a cross-aligned nanowire network based on a layer-by-layer assembly strategy. Compared to randomly distributed AgNWs networks (11.17 Ω sq^-1, 85.2%), the cross-aligned AgNWs network achieved simultaneous welding of nanowire junctions during thermal annealing, further enhancing the optoelectronic performance (10.8 Ω sq^-1, 90.3%) of the AgNWs network, resulting in a superior figure of merit value of 421.