Search Results (15)

Cancer, a significant cause of mortality, necessitates improved drug delivery strategies. Exosomes, as natural drug carriers, offer a more efficient, targeted, and less toxic drug delivery system compared to direct dispersal methods via ingestion or injection. To be successfully implemented as drug carriers, efficient loading of drugs into exosomes is crucial, and a deeper understanding of the loading mechanism remains to be solved. This study introduces surface-enhanced Raman scattering (SERS) to monitor drug loading efficacy at the single vesicle level. By enhancing the Raman signal, SERS overcomes limitations in Raman spectroscopy. A gold nanopyramids array-based SERS substrate assesses exosome heterogeneity in drug-loading capabilities with the help of single-layer graphene for precise quantification. This research advances targeted drug delivery by presenting a more efficient method of evaluating drug-loading efficiency into individual exosomes through SERS-based monitoring. Furthermore, the study explores leveraging osmotic pressure variations, enhancing the efficiency of drug loading into exosomes. Full article

The presented research is the seed of a vision for the development of a waste-for-product strategy. Following this concept, various synthetic solutions containing low concentrations of platinum group metals were used to model their recovery and to produce catalysts. This is also the first report that shows the method for synthesis of a pyramid-like structure deposited on activated carbon composed of Pd and Pt. This unique structure was obtained from a mixture of highly diluted aqueous solutions containing both metals and chloride ions. The presence of functional groups on the carbon surface and experimental conditions allowed for: the adsorption of metal complexes, their reduction to metal atoms and enabled further hierarchical growth of the metal layer on the carbon surface. During experiments, spherical palladium and platinum nanoparticles were obtained. The addition of chloride ions to the solution promoted the hierarchical growth and formation of palladium nanopyramids, which were enriched with platinum nanoparticles. The obtained materials were characterized using UV–Vis, Raman, IR spectroscopy, TGA, SEM/EDS, and XRD techniques. Moreover, Pd@ROY, Pt@ROY, and Pd-Pt@ROY were tested as possible electrocatalysts for hydrogen evolution reactions. Full article

Perovskite solar cells (PSCs) still suffer from varying degrees of optical and electrical losses. To enhance the light decoupling and capture ability of Planar PSCs, an ultra-thin PSC structure with an Al₂O₃ pyramid anti-reflection layer (Al₂O₃ PARL) is proposed. The effect of the structure of the Al₂O₃ PARL on the photoelectric performance of PSCs was investigated by changing various parameters. Under the AM1.5 solar spectrum (300–800 nm), the average light absorption rates and quantum efficiency (QE) of PSCs containing pyramid-array textured rear layers (PARLs) were significantly higher than those of planar PSCs. The Al₂O₃ PARL-based PSCs achieved a light absorption rate of 96.05%. Additionally, electrical simulations were performed using the finite element method (FEM) to calculate the short-circuit current density (J_SC), open-circuit voltage (V_OC), and maximum power (Pmax). Based on the maximum value of the average light absorbance, the geometric structure of the Al₂O₃ pyramid PSCs was optimized, and the optimization results coincided with the J_SC and QE results. The results of the electrical simulation indicated that the maximum J_SC was 23.54 mA/cm². Additionally, the J_SC of the Al₂O₃ pyramid PSCs was 22.73% higher than that of planar PSCs, resulting in a photoelectric conversion efficiency (PCE) of 24.34%. As a result, the photoelectric conversion rate of the solar cells increased from 14.01% to 17.19%. These findings suggest that the presence of the Al₂O₃ PARL enhanced photon absorption, leading to an increase in electron–hole pairs and ultimately improving the photocurrent of the solar cells. Full article

Ion-flow-stimulated roughening transition is a phenomenon that may prove useful in the hierarchical structuring of nanostructures. In this work, we have investigated theoretically and experimentally the surface texturing of single-crystal and multi-crystalline silicon wafers irradiated using ion-beam flows. In contrast to previous studies, ions had relatively low energies, whereas flow densities were high enough to induce a quasi-liquid state in the upper silicon layers. The resulting surface modifications reduced the wafer light reflectance to values characteristic of black silicon, widely used in solar energetics. Features of nanostructures on different faces of silicon single crystals were studied numerically based on the mesoscopic Monte Carlo model. We established that the formation of nano-pyramids, ridges, and twisting dune-like structures is due to the stimulated roughening transition effect. The aforementioned variety of modified surface morphologies arises due to the fact that the effects of stimulated surface diffusion of atoms and re-deposition of free atoms on the wafer surface from the near-surface region are manifested to different degrees on different Si faces. It is these two factors that determine the selection of the allowable “trajectories” (evolution paths) of the thermodynamic system along which its Helmholtz free energy, F, decreases, concomitant with an increase in the surface area of the wafer and the corresponding changes in its internal energy,$U$ ($dU>0$), and entropy,$S$ ($dS>0$), so that $dF=dU – TdS<0$, where $T$ is the absolute temperature. The basic theoretical concepts developed were confirmed in experimental studies, the results of which showed that our method could produce, abundantly, black silicon wafers in an environmentally friendly manner compared to traditional chemical etching. Full article

ZnMn₂O₄ spinels are prepared by a simple hydrothermal route with control of the reaction time, ranging from 6 h to 18 h. The evolution of the structural and morphological parameters under the effect of time was analyzed by XRD, ATR-FTIR, XPS, and SEM-EDS. The XRD results show that for longer reaction times (18 h), the ZnMn₂O₄ spinel samples present a tetragonal structure with high crystallinity and an average crystallite size of 32.3 ± 1.7 nm, larger than those obtained for 6 h and 12 h. The ATR-FTIR spectra confirm the structural results, with well-defined peaks related to stretching vibrations of M-O (M = Zn, Mn) functional groups. XPS reveals the co-existence of several metal oxides and hydroxides at the outermost surface. SEM analysis shows that the samples present a pyramid morphology, better defined at 18 h, with an average particle size of 6.2 ± 1.5 µm. EDS analysis of ZnMn₂O₄ (18 h) reveals atomic ratios of 0.45, 0.22, and 0.50 for Zn/Mn, Zn/O, and Mn/O, respectively, in good agreement with the expected values. Based on the CVs, the synthesized ZnMn₂O₄ samples formed at 18 h showed the most promising electrochemical properties, with a specific capacity of 102 F g⁻¹, offering great potential in supercapacitor applications. Full article

Epitaxial GaN nanostructures are developed, and the influence of the AlN buffer layer (temperature modulation) on material characteristics and optoelectronic device application is assessed. The AlN buffer layer was grown on a Si (111) substrate at varying temperatures (770–830 °C), followed by GaN growth using plasma-assisted molecular beam epitaxy. The investigation revealed that the comparatively lower temperature AlN buffer layer was responsible for stress and lattice strain relaxation and was realized as the GaN nano-obelisk structures. Contrarily, the increased temperature of the AlN growth led to the formation of GaN nanopyramidal and nanowax/wane structures. These grown GaN/AlN/Si heterostructures were utilized to develop photodetectors in a metal–semiconductor–metal geometry format. The performance of these fabricated optoelectronic devices was examined under ultraviolet illumination (UVA), where the GaN nano-obelisks-based device attained the highest responsivity of 118 AW⁻¹. Under UVA (325 nm) illumination, the designed device exhibited a high detectivity of 1 × 10¹⁰ Jones, noise equivalent power of 1 × 10⁻¹² WHz^−1/2, and external quantum efficiency of 45,000%. The analysis revealed that the quality of the AlN buffer layer significantly improved the optoelectronic performance of the device. Full article

ZnO nanostructures were synthesized by a combination of non-aqueous and aqueous sol-gel techniques to obtain morphologically different ZnO nanostructures, nanorods, and nanopyramids, featuring oxygen vacancies-rich exposed lattice faces and exhibiting different catalytic properties and activity. In particular, ZnO nanorods with high surface area (36 m²/g) were obtained through a rapid, scalable, and convenient procedure. The materials were tested for complete methane oxidation as an important benchmark reaction that is sensitive to surface area and to the availability of oxygen vacancies. Simple ZnO nanorods derived from nanosized quantum dots showed the best catalytic performance that compared well to that of several literature-reported perovskites, mixed metal oxides, and single-metal oxides in terms of T₅₀ (576 °C) and T₉₀ (659 °C) temperatures. Such a result was attributed to their high surface-to-volume ratio enhancing the availability of catalytically active sites such as oxygen vacancies whose abundance further increased following catalytic application at high temperatures. The latter effect allowed us to maintain a nearly stable catalytic performance with over 90% conversion for 12 h at 700 °C despite sintering. This research shows that ZnO-based nanomaterials with a high surface area are viable alternatives to oxides of commonly applied (but of potentially limited availability) transition metals (La, Mn, Co, Ni) for the complete combustion of methane when working at moderate temperatures (600–700 °C). Full article

In this article, we present a systematic investigation on a multistep nanosphere lithography technique to uncover its potential in fabricating a wide range of two- and three-dimensional nanostructures. A tilted (polar angle) electron beam shower on a nanosphere mask results in an angled shadow mask deposition. The shape of the shadow also depends on the azimuthal angle of the mask sitting on top of the substrate. We performed angled shadow mask depositions with systematic variation of these two angular parameters, giving rise to complex nanostructures (down to 50 nm), repeated over a large area without defect. In this article, nanosphere lithography with two- and four-fold azimuthal symmetry was studied at constant tilt angles followed by variations in tilt without azimuthal rotation of the substrate. Finally, both angular parameters were simultaneously varied. The structure of shadow crystals was explained using Matlab simulation. This work stretches the horizons of nanosphere lithography, opening up new scopes in plasmonic and magnonic research. Full article

Inspired by the knowledge of the thermocatalytic CO₂ reduction process, novel nanocrystalline CuZnAl-oxide based catalysts with pyramidal mesoporous structures are here proposed for the CO₂ electrochemical reduction under ambient conditions. The XPS analyses revealed that the co-presence of ZnO and Al₂O₃ into the Cu-based catalyst stabilize the CuO crystalline structure and introduce basic sites on the ternary as-synthesized catalyst. In contrast, the as-prepared CuZn- and Cu-based materials contain a higher amount of superficial Cu⁰ and Cu¹⁺ species. The CuZnAl-catalyst exhibited enhanced catalytic performance for the CO and H₂ production, reaching a Faradaic efficiency (FE) towards syngas of almost 95% at −0.89 V vs. RHE and a remarkable current density of up to 90 mA cm⁻² for the CO₂ reduction at −2.4 V vs. RHE. The physico-chemical characterizations confirmed that the pyramidal mesoporous structure of this material, which is constituted by a high pore volume and small CuO crystals, plays a fundamental role in its low diffusional mass-transfer resistance. The CO-productivity on the CuZnAl-catalyst increased at more negative applied potentials, leading to the production of syngas with a tunable H₂/CO ratio (from 2 to 7), depending on the applied potential. These results pave the way to substitute state-of-the-art noble metals (e.g., Ag, Au) with this abundant and cost-effective catalyst to produce syngas. Moreover, the post-reaction analyses demonstrated the stabilization of Cu₂O species, avoiding its complete reduction to Cu⁰ under the CO₂ electroreduction conditions. Full article

Two multilayer (ML) structures, composed of five layers of silicon-rich oxide (SRO) with different Si contents and a sixth layer of silicon-rich nitride (SRN), were deposited by low pressure chemical vapor deposition. These SRN/SRO MLs were thermally annealed at 1100 °C for 180 min in ambient N₂ to induce the formation of Si nanostructures. For the first ML structure (MLA), the excess Si in each SRO layer was about 10.7 ± 0.6, 9.1 ± 0.4, 8.0 ± 0.2, 9.1 ± 0.3 and 9.7 ± 0.4 at.%, respectively. For the second ML structure (MLB), the excess Si was about 8.3 ± 0.2, 10.8 ± 0.4, 13.6 ± 1.2, 9.8 ± 0.4 and 8.7 ± 0.1 at.%, respectively. Si nanopyramids (Si-NPs) were formed in the SRO/Si substrate interface when the SRO layer with the highest excess silicon (10.7 at.%) was deposited next to the MLA substrate. The height, base and density of the Si-NPs was about 2–8 nm, 8–26 nm and ~6 × 10¹¹ cm⁻², respectively. In addition, Si nanocrystals (Si-ncs) with a mean size of between 3.95 ± 0.20 nm and 2.86 ± 0.81 nm were observed for the subsequent SRO layers. Meanwhile, Si-NPs were not observed when the excess Si in the SRO film next to the Si-substrate decreased to 8.3 ± 0.2 at.% (MLB), indicating that there existed a specific amount of excess Si for their formation. Si-ncs with mean size of 2.87 ± 0.73 nm and 3.72 ± 1.03 nm were observed for MLB, depending on the amount of excess Si in the SRO film. An enhanced photoluminescence (PL) emission (eight-fold more) was observed in MLA as compared to MLB due to the presence of the Si-NPs. Therefore, the influence of graded silicon content in SRN/SRO multilayer structures on the formation of Si-NPs and Si-ncs, and their relation to the PL emission, was analyzed. Full article

Different patterns can be created on the surface of growing crystals, among which the step bunches and/or step meanders are two of the most studied. The Ehrlich–Schwoebel effect at the surface steps is considered one of the “usual suspects” of such patterning. A direct step barrier is when it is easier to attach a particle to the step from the lower terrace than from the upper terrace. Thus, during the process of crystal growth leads to the formation of meanders, while an inverse barrier leads to step bunching. Based on our vicinal Cellular Automaton model, but this time in (2 + 1)D, we show that the combination of a direct and inverse step barrier and the proper selection of the potential of the well between them leads to the formation of bunched step structures. Following this is the formation of anti-bands. In addition, changing the height of the direct step barrier leads to the growth of nanocolumns, nanowires, and nanopyramids or meanders, in the same system. Full article

In this work, the structural, optical, morphological, and sensing features of tungsten oxide (WO₃) thin film deposited on a silicon substrate via hot-filament chemical vapor deposition (HFCVD) are described. The experimental characterization tools, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet-visible (UV-Vis), and Fourier transform infra-red (FTIR) spectroscopies, etc., were used to determine the properties of WO₃ NPys thin films. The grown WO₃ thin film illustrated closely packed porous pyramidal nanostructures (NPys) of improved grain size properties. The diffraction analysis revealed (100) and (200) of WO₃ phases, suggesting the classic monoclinic crystal WO₃ structure. HFCVD grown WO₃ NPys thin film was employed as electro-active electrode for detecting ethylenediamine in 10 mL of 0.1 M phosphate buffer solution (PBS) by varying the ethylenediamine concentrations from 10 μM to 200 μM at room temperature. With a detection of limit (LOD) of ~9.56 μM, and a quick reaction time (10 s), the constructed chemical sensor achieved a high sensitivity of ~161.33 μA μM⁻¹ cm⁻². The durability test displayed an excellent stability of electrochemical sensor by maintaining over 90% sensitivity after 4 weeks of operation. This work provides a strategy for a facile preparation of WO₃ NPys thin film electrode for sensor applications. Full article

We report here a novel “one-pot” approach for the controlled growth and organization of Prussian blue nanostructures on three different surfaces: pure Au⁰, cysteamine-functionalized Au⁰, and SiO₂-supported lipid bilayers with different natures of lipids. We demonstrate that fine control over the size, morphology, and the degree and homogeneity of the surface coverage by Prussian Blue (PB) nanostructures may be achieved by manipulating different parameters, which are the precursor concentration, the nature of the functional groups or the nature of lipids on the surfaces. This allows the growth of isolated PB nanopyramids and nanocubes or the design of thin dense films over centimeter square surfaces. The formation of unusual Prussian blue nanopyramids is discussed. Finally, we demonstrate, by using experimental techniques and theoretical modeling, that PB nanoparticles deposited on the gold surface exhibit strong photothermal properties, permitting a rapid temperature increase up to 90 °C with a conversion of the laser power of almost 50% for power source heat. Full article

Tuning the intrinsic structural and stoichiometric properties by different means is used for increasing the green energy production efficiency of complex oxide materials. Here, we report on the formation of self-assembled nanodomains and their effects on the photoelectrochemical (PEC) properties of LaFeO₃ (LFO) epitaxial thin films as a function of layer’s thickness. The variation with the film’s thickness of the structural parameters such as in-plane and out-of-plane crystalline coherence length and the coexistence of different epitaxial orientation—<100>SrTiO₃//<001> LFO, <100>SrTiO₃//<110> LFO and [110] LFO//[10] STO, as well as the appearance of self-assembled nanodomains for film’s thicknesses higher than 14 nm, is presented. LFO thin films exhibit different epitaxial orientations depending on their thickness, and the appearance of self-assembled nanopyramids-like domains after a thickness threshold value has proven to have a detrimental effect on the PEC functional properties. Using Nb:SrTiO₃ as conductive substrate and 0.5 M NaOH aqueous solution for PEC measurements, the dependence of the photocurrent density and the onset potential vs. RHE on the structural and stoichiometric features exhibited by the LFO photoelectrodes are unveiled by the X-ray diffraction, high-resolution transmission electron microscopy, ellipsometry, and Rutherford backscattering spectroscopy results. The potentiodynamic PEC analysis has revealed the highest photocurrent density J_photocurrent values (up to 1.2 mA/cm²) with excellent stability over time, for the thinnest LFO/Nb:SrTiO₃ sample, both cathodic and anodic behavior being noticed. Noticeably, the LFO thin film shows unbiased hydrogen evolution from water, as determined by gas chromatography in aqueous 0.5 M NaOH solution under constant illumination. Full article

The present investigation reported on a novel oxygen-assisted etching growth method that can directly transform wafer-scale plain VO₂ thin films into pyramidal-like VO₂ nanostructures with highly improved field-emission properties. The oxygen applied during annealing played a key role in the formation of the special pyramidal-like structures by introducing thin oxygen-rich transition layers on the top surfaces of the VO₂ crystals. An etching related growth and transformation mechanism for the synthesis of nanopyramidal films was proposed. Structural characterizations confirmed the formation of a composite VO₂ structure of monoclinic M1 (P21/c) and Mott insulating M2 (C2/m) phases for the films at room temperature. Moreover, by varying the oxygen concentration, the nanocrystal morphology of the VO₂ films could be tuned, ranging over pyramidal, dot, and/or twin structures. These nanopyramidal VO₂ films showed potential benefits for application such as temperature−regulated field emission devices. For one typical sample deposited on a 3-inch silicon substrate, its emission current (measured at 6 V/μm) increased by about 1000 times after the oxygen-etching treatment, and the field enhancement factor β reached as high as 3810 and 1620 for the M and R states, respectively. The simple method reported in the present study may provide a protocol for building a variety of large interesting surfaces for VO₂-based device applications. Full article