Nanomaterials最新文献

Indium Arsenide is a III-V semiconductor with low electron effective mass, a small band gap, strong spin-orbit coupling, and a large g-factor. These properties and its surface Fermi level pinned in the conduction band make InAs a good candidate for developing superconducting solid-state quantum devices. Here, we report the epitaxial growth of very thin InAs layers with thicknesses ranging from 12.5 nm to 500 nm grown by Molecular Beam Epitaxy on In_xAl_1-xAs metamorphic buffers. Differently than InAs substrates, these buffers have the advantage of being insulating at cryogenic temperatures, which allows for multiple device operations on the same wafer and thus making the approach scalable. The structural properties of the InAs layers were investigated by high-resolution X-ray diffraction, demonstrating the high crystal quality of the InAs layers. Furthermore, their transport properties, such as total and sheet carrier concentration, sheet resistance, and carrier mobility, were measured in the van der Pauw configuration at room temperature. A simple conduction model was employed to quantify the surface, bulk, and interface contributions to the overall carrier concentration and mobility.

The in situ combination of plasma-enhanced chemical vapor deposition (PECVD) and vacuum evaporation in the same vacuum chamber allowed us to integrate germanium nanocrystals (Ge NCs) into hydrogenated amorphous silicon carbide (a-SiC:H) thin films deposited from monomethyl silane diluted with hydrogen. Transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy were used for the microscopic characterization, while photothermal deflection spectroscopy (PDS) and near-infrared photoluminescence spectroscopy (NIR PL) were for optical characterization. The presence of Ge NCs embedded in the amorphous a-Si:C:H thin films was confirmed by TEM and EDX. The embedded Ge NCs increased optical absorption in the NIR spectral region. The quenching of a-SiC:H NIR PL due to the presence of Ge indicates that the diffusion length of free charge carriers in a-SiC:H is in the range of a few tens of nm, an order of magnitude less than in a-Si:H. The optical properties of a-SiC:H films were degraded after vacuum annealing at 550 °C.

This study investigated the influence of parameters such as pH condition, polyelectrolyte concentration, polymer ratio, and order of addition of the commercial polyelectrolytes chitosan and iota-carrageenan (ι-carrageenan) on the formation of polymeric nanoparticles in suspension (coacervates). A preliminary purification step of the polymers was essential for obtaining stable nanoparticles with small sizes as impurities, particularly metal ions that interfere with complexation, are removed by dialysis. Microparticles (13.5 μm in dry diameter) are obtained when aliquots of chitosan solution are poured into the ι-carrageenan solution. In general, an excess of chitosan results in the formation of agglomerated particles. The addition of an aliquot of ι-carrageenan solution (30 mL at 0.6 mg/mL and pH 4.0) to the chitosan solution (6.0 mL at 0.3 mg/mL and pH 4.0) leads to dispersed nanoparticles with a hydrodynamic radius of 278 ± 5 nm, a zeta potential of -31 ± 3 mV, and an average dry diameter of 45 ± 11 nm. The hydrodynamic radius increases as the pH rises. The partial deprotonation of ι-carrageenan chains enhances the interaction with water molecules, causing the particles to swell. These findings contribute to the fundamental understanding of polyelectrolyte complexation processes in aqueous suspension and provide insights for developing stable nanomaterials for potential practical applications.

A copper-based nanoenzyme (Cu-BL) co-modified by L-L-lysine and 2-2-amino terephthalic acid has laccase-like activity and fluorescence characteristics. Based on this, a colorimetric and fluorescent dual-mode sensor was developed to visually and quantitatively detect tetracycline antibiotics (TCs), including tetracycline (TC), chlortetracycline (CTC), and oxytetracycline (OTC). In the colorimetric detection system, TCs can inhibit the generation of singlet oxygen (¹O₂) and weaken the ability of 2,4-dichlorophenol (2,4-DP) to be oxidized into pink-colored quinone substances. The linear ranges are 0.5-80 μM, 1-80 μM, and 0.25-80 μM, and the detection limits are 0.27 μM, 0.22 μM, and 0.26μM, respectively. In addition, due to the inner filter effect, tetracycline antibiotics can interact with Cu-BL, and with the increase in tetracycline antibiotic concentration, the fluorescence intensity will decrease. In addition, the smartphone sensing platform is combined with the colorimetric signal for the rapid and visual quantitative detection of tetracycline antibiotics. Generally speaking, the colorimetric/fluorescence dual-mode sensor demonstrates good stability, high specificity, and strong anti-interference capabilities, highlighting its practical application potential. This work is expected to offer novel insights for the development of multifunctional nanoenzymes and the integration of a multi-mode sensing platform.

In cases of severe injuries or burns, skin grafts (scaffolds) are often required as skin substitutes. In order not to harm the patient or the donor, biodegradable and biocompatible materials are used, which validates the search for heterografts such as poly (L-lactic acid)-PLA. However, natural polymers applied to the skin suffer great degradation in environments with large amounts of carbon and water or via binders with considerable resistivity, which implies little durability due to their low ductility. For the proposal, this work investigates PLA-based scaffolds modified with a mixture of pseudoboehmite (PB) and graphene oxide (GO), produced via the sol-gel route. The nanomaterials are incorporated into the polymer at different loadings, seeking to improve mechanical and thermal properties. Analyses via SEM, EDS, and XRD confirm the presence and distribution of these fillers. Tensile and flexural tests indicate that adding the filler can increase stress resistance, prevent deformations before failure, and increase toughness when compared to pure PLA.

The carcinogenic potential of MWCNTs is not well defined. Currently, IARC has classified MWCNT-7 as a Group 2 B material, possibly carcinogenic to humans, and all other MWCNTs as Group 3 materials, inadequate evidence in experimental animals for their carcinogenicity and not classifiable as to their carcinogenicity to humans. In this review we discuss studies that investigated the lung toxicity of well characterized MWCNTs in mice and rats. Intraperitoneal and intrascrotal injection studies identified rigid MWCNTs as hazardous materials. The assessment of lung toxicity of MWCNTs in short and medium term instillation and inhalation studies were not conclusive; therefore, these studies do not confirm the hazard of MWCNTs. However, two-year carcinogenicity studies indicate that MWCNT-7 and other MWCNTs, both thick rigid MWCNTs and thin flexible MWCNTs, are carcinogenic in test animals. Therefore, the carcinogenicity of MWCNTs in experimental animals should be reassessed.

Cu-containing and Ce-modified OMS-2 catalysts were prepared at various calcination temperatures using the hydrothermal method and tested for low-temperature CO oxidation. The structure, chemical compositions, and physical-chemical properties of the catalysts were characterized using XRD, N₂ physisorption, XRF, Raman spectroscopy, SEM, high-resolution TEM with EDX, TPR-H₂, and XPS. The incorporation of Cu into the Ce-OMS-2 sample facilitated the transformation of pyrolusite into cryptomelane, as confirmed by Raman spectroscopy data. In the light-off mode, the Cu/Ce-OMS-2-300 and Cu/OMS-2 samples exhibited higher activity in low-temperature CO oxidation (T₉₀ = 115 and 121 °C, respectively) compared to sample Cu/Ce-OMS-2-450. After a long-run stability test, the Cu/Ce-OMS-X samples demonstrated excellent performance: the T₈₀ increased by 16% and 7% for the samples calcined at 300 °C and 450 °C, respectively, while the T₈₀ for the Cu/OMS-2 increased by 40%. The Cu/OMS-2 and Cu/Ce-OMS-2-300 samples were found to have an increased content of nanodispersed copper sites on their surfaces. These copper sites contributed to the formation of the Cu²⁺-O-Mn⁴⁺ interface, which is responsible for the CO oxidation. The presence of Ce³⁺ in the catalyst was found to increase its stability in the presence of water vapor due to the higher reoxidation ability in comparison with Ce-free sample Cu/OMS-2.

The advent of two-dimensional (2D) ferroelectrics offers a new paradigm for device miniaturization and multifunctionality. Recently, 2D α-In₂Se₃ and related III-VI compound ferroelectrics manifest room-temperature ferroelectricity and exhibit reversible spontaneous polarization even at the monolayer limit. Here, we employ first-principles calculations to investigate group-III selenide van der Waals (vdW) heterojunctions built up by 2D α-In₂Se₃ and α-Ga₂Se₃ ferroelectric (FE) semiconductors, including structural stability, electrostatic potential, interfacial charge transfer, and electronic band structures. When the FE polarization directions of α-In₂Se₃ and α-Ga₂Se₃ are parallel, both the α-In₂Se₃/α-Ga₂Se₃ P↑↑ (UU) and α-In₂Se₃/α-Ga₂Se₃ P↓↓ (NN) configurations possess strong built-in electric fields and hence induce electron-hole separation, resulting in carrier depletion at the α-In₂Se₃/α-Ga₂Se₃ heterointerfaces. Conversely, when they are antiparallel, the α-In₂Se₃/α-Ga₂Se₃ P↓↑ (NU) and α-In₂Se₃/α-Ga₂Se₃ P↑↓ (UN) configurations demonstrate the switchable electron and hole accumulation at the 2D ferroelectric interfaces, respectively. The nonvolatile characteristic of ferroelectric polarization presents an innovative approach to achieving tunable n-type and p-type conductive channels for ferroelectric field-effect transistors (FeFETs). In addition, in-plane biaxial strain modulation has successfully modulated the band alignments of the α-In₂Se₃/α-Ga₂Se₃ ferroelectric heterostructures, inducing a type III-II-III transition in UU and NN, and a type I-II-I transition in UN and NU, respectively. Our findings highlight the great potential of 2D group-III selenides and ferroelectric vdW heterostructures to harness nonvolatile spontaneous polarization for next-generation electronics, nonvolatile optoelectronic memories, sensors, and neuromorphic computing.

A series of AlGaN/GaN high-electron-mobility transistor (HEMT) structures, with an AlN thin buffer, GaN thick layer and Al_0.25Ga_0.75N layer (13-104 nm thick), is prepared by metal-organic chemical vapor deposition and investigated via multiple techniques. Spectroscopic ellipsometry (SE) and temperature-dependent measurements and penetrative analyses have achieved significant understanding of these HEMT structures. Bandgaps of AlGaN and GaN are acquired via SE-deduced relationships of refraction index n and extinguish coefficient k vs. wavelength λ in a simple but straightforward way. The optical constants of n and k, and the energy gap E_g of AlGaN layers, are found slightly altered with the variation in AlGaN layer thickness. The Urbach energy E_U at the AlGaN and GaN layers are deduced. High-resolution X-ray diffraction and calculations determined the extremely low screw dislocation density of 1.6 × 10⁸ cm^-2. The top AlGaN layer exhibits a tensile stress influenced by the under beneath GaN and its crystalline quality is improved with the increase in thickness. Comparative photoluminescence (PL) experiments using 266 nm and 325 nm two excitations reveal and confirm the 2DEG within the AlGaN-GaN HEMT structures. DUV (266 nm) excitation Raman scattering and calculations acquired carrier concentrations in compatible AlGaN and GaN layers.

Area-selective atomic layer deposition (AS-ALD) is a technique utilized for the fabrication of patterned thin films in the semiconductor industry due to its capability to produce uniform and conformal structures with control over thickness at the atomic scale level. In AS-ALD, surfaces are functionalized such that only specific locations exhibit ALD growth, thus leading to spatial selectivity. Self-assembled monolayers (SAMs) are commonly used as ALD inhibiting agents for AS-ALD. However, the choice of organic molecules as viable options for AS-ALD remains limited and the precise effects of ALD nucleation and exposure to ALD conditions on the structure of SAMs is yet to be fully understood. In this work, we investigate the potential of small molecule carboxylates as ALD inhibitors, namely benzoic acid and two of its derivatives, 4-trifluoromethyl benzoic acid (TBA), and 3,5-Bis (trifluoromethyl)benzoic acid (BTBA) and demonstrate that monolayers of all three molecules are viable options for applications in ALD blocking. We find that the fluorinated SAMs are better ALD inhibitors; however, this property arises not from the hydrophobicity but the coordination chemistry of the SAM. Using nanoscale infrared spectroscopy, we probe the buried monolayer interface to demonstrate that the distribution of carboxylate coordination states and their evolution is correlated with ALD growth, highlighting the importance of the interfacial chemistry in optimizing and assessing ALD inhibitors.