Recently, vanadium oxides and other semiconductor materials have been intensively studied to use them as nonplasmonic substrates for surface-enhanced Raman scattering (SERS) spectroscopy due to their ...advantages such as greater uniformity, stability, and spectral reproducibility compared to plasmonic ones. The combination of vanadium pentoxide nanoparticles (V2O5 NPs) with nanostructures of noble metals has shown considerable promise for enhancing the SERS signal, while maintaining the aforementioned advantages. We prepared V2O5/Au NP films by a novel, simple, fully solvent- and linker-free method: the gas-phase synthesis of vanadium NPs followed by their thermal annealing at 550 °C to obtain V2O5 NP films, which were subsequently decorated with Au nanoislands. Using methylene blue (MB) solution as a test analyte, we observed a significant enhancement of the SERS signal (up to 65 times) from the V2O5/Au composite compared to those from pure V2O5 substrates. The SERS enhancement in this case arises from the synergy of electromagnetic and chemical (charge-transfer) enhancement. The deposition of Au on the V2O5 surface increases the charge-transfer contribution. Moreover, the additional enhancement is achieved due to electromagnetic field coupling between V2O5 and Au or between neighboring Au nanostructures. The observation of two maxima of MB SERS signal from the V2O5/Au heterostructure for various Au deposition times brings new insights into the SERS mechanism of the semiconductor–metal heterostructure. Spectral mapping across the V2O5/Au substrates shows excellent homogeneity and spectral reproducibility (RSD of the SERS signal less than 10%). This study introduces an important step in designing novel semiconductor–metal SERS-active substrates. Our V2O5/Au heterostructures represent highly attractive substrates with improved stability and spectral reproducibility as compared to other nonplasmonic and plasmonic ones.
A mechanical time-of-flight filter intended for measurement of velocities of nanoparticles exiting a gas aggregation source has been developed. Several configurations maximizing simplicity, ...throughput or resolution are suggested and investigated both theoretically and experimentally. It is shown that the data measured using such filters may be easily converted to the real velocity distribution with high precision. Furthermore, it is shown that properly designed filters allow for the monitoring of the velocity of nanoparticles even at the conditions with extremely low intensity of the nanoparticle beam.
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•SERS activity of gas-phase synthesized of Ag/C:H:N:O NPs coatings is tested.•The analytical enhancement factor is found to be 1.1 × 106 for methylene blue.•The superior SERS activity ...of produced films is due to their mesoporous character.•These results pave the way for the solvent-free production of SERS-active platforms.
Rapid development in the field of detection of biomolecules by surface-enhanced Raman spectroscopy (SERS) is enabled by enormous progress in the nanofabrication that nowadays allows for the tailor-made production of nanomaterials that can serve as effective and reliable SERS-active platforms. Among others, heterogeneous mesoporous coatings constitute an important class of nanomaterials that receives increasing attention. In this study, we investigate the possibility of producing such nanomaterials using a novel, one-step, and fully solvent-free technique. This approach employs the in-flight decoration of gas-phase synthesized C:H:N:O plasma polymer cores with nanometre-sized silver nanoparticles. Such physically produced Ag/C:H:N:O core-satellite nanoparticles upon deposition on a planar substrate spontaneously form mesoporous nanoparticle films with SERS-active Ag nanoparticles evenly distributed on the surface of supporting C:H:N:O cores. As shown, such produced nanomaterials exhibit, due to their structure, the SERS enhancement factor of (1.1 ± 0.2) × 106, i.e., the enhancement factor one order of magnitude higher than the value 1 × 105 typically reported for silver nanostructures prepared by commonly used magnetron sputtering onto planar substrates.
The early stage of nanoparticle formation in gas aggregation systems is studied with the ambition to reveal the role of atomic dimers acting as cluster nuclei. The initial formation of a dimer ...nucleus, serving as a seed for subsequent atom attachment growth, is believed to be the bottleneck of the nanoparticle gas-aggregated synthesis. We thus examined the nature of the underlying process by employing energy-resolved mass-spectrometry and imaging of deposited nanoparticles. The production of dimers with origin in the discharge gas phase (ArCu+, Ar2+) and dimers preferentially sputtered directly from the target (Cu2+) was studied. The study demonstrates that sputtered Cu2+ dimers, carrying the high energy tail of Thompson energy distribution, play a major role as agents responsible for the formation of initial cluster nuclei, followed by a significant contribution of ArCu+; the population of these dimers is proportional to nanoparticle transported mass to the substrate. The proposed mechanism and the role of the dimer might be material independent since the qualitative agreement was also obtained for Ag NPs.
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•Efficiency of early-stage nanoparticle growth in gas aggregation processes•Energy-resolved mass spectrometry of dimer species in plasma discharge•Tailored and controlled magnetron sputtering of dimers from the target•Nanoparticle growth is strongly linked to directly sputtered dimers.
The book represents a collection of papers from Special Issue “Formation of Advanced Nanomaterials by Gas-Phase Aggregation” published in journal Applied Nano. It contains review and original ...articles covering a range of topics on the growth of clusters/nanoparticles using gas-phase aggregation approaches, the application of cluster beams for the formation of nanomaterials with advanced properties and specific nanostructures as well as providing new fundamental insights on nanoscale properties of materials.
One of the leading causes of failure for any bone implant is implant-associated infections. The implant–bone interface is in fact the crucial site of infection where both the microorganisms and cells ...compete to populate the newly introduced implant surface. Most of the work dealing with this issue has focused on the design of implant coatings capable of preventing infection while ignoring cell proliferation or vice versa. The present study is therefore focused on investigating the antibacterial and biological properties of nanocomposite coatings based on an amorphous hydrocarbon (a-C:H) matrix containing silver nanoparticles (AgNPs). a-C:H coatings with varying silver concentrations were generated directly on medical grade titanium substrates using a combination of a gas aggregation source (GAS) and a plasma-enhanced chemical vapor deposition (PE-CVD) process. The obtained results revealed that the surface silver content increased from 1.3 at % to 5.3 at % by increasing the used DC magnetron current in the GAS from 200 to 500 mA. The in vitro antibacterial assays revealed that the nanocomposites with the highest number of silver content exhibited excellent antibacterial activities resulting in a 6-log reduction of Escherichia coli and a 4-log reduction of Staphylococcus aureus after 24 h of incubation. An MTT assay, fluorescence live/dead staining, and SEM microscopy observations of MC3T3 cells seeded on the uncoated and coated Ti substrates also showed that increasing the amount of AgNPs in the nanocomposites had no notable impact on their cytocompatibility, while improved cell proliferation was especially observed for the nanocomposites possessing a low amount of AgNPs. These controllable Ag/a-C:H nanocomposites on Ti substrates, which simultaneously provide an excellent antibacterial performance and good biocompatibility, could thus have promising applications in orthopedics and other biomedical implants.
Gas aggregation sources have become a valuable tool for the effective production of nanoparticles and nanoparticle films. In some cases (e.g. during in-flight coating of nanoparticles or interaction ...between nanoparticles and substrate), the critical parameter that influences the applicability of these sources and properties of fabricated nanomaterials is the velocity of produced nanoparticles. Naturally, to control the speed of nanoparticles, it is crucial to determine how it is influenced by process parameters. A mechanical time-of-flight filter has been used to measure the velocities of nanoparticles exiting a magnetron-based gas aggregation source. Nanoparticle velocities have been investigated for various deposition conditions, including aggregation chamber pressure from 20 to 100 Pa, magnetron current from 100 to 500 mA and deposition chamber pressure from 0.015 to 2.5 Pa. Nanoparticles may be accelerated in the area around the exit orifice and decelerated by the background gas in the deposition chamber. This allows tailoring the nanoparticle velocity in the range from 10 m s−1 up to over 100 m s−1. Furthermore, the dependence of the velocity of nanoparticles on their size was found to obey a simple power law. Therefore, the filter may be used not only as a velocity filter but also as a mass filter.
•High resolution nanoparticle velocity measurement outside of gas aggregation source.•Measurement of velocity of nanoparticles including neutral ones.•Mass filtration of nanoparticles including neutral ones.•Nanoparticles deceleration by background gas.
Abstract
Plasma polymer nanoparticles (pp‐NPs) are relatively easy to produce by plasma‐based gas aggregation sources. However, as experimentally evidenced in this study for the case of C:H:N:O ...pp‐NPs, pp‐NPs are unlike metal/metal oxide nanoparticles prone to reflection from the substrate if they hit it with too high a speed. This may result in little or no deposition rate even though the nanoparticle beam is very intense. As is shown, the deposition of pp‐NPs can be promoted either by the adjustment of their speed before they reach the substrate or by a proper selection of a substrate. Concerning the latter, enhanced capturing of pp‐NPs was observed on structured or liquid substrates.
In this study, we have analyzed experimentally different strategies for controlling the morphology of vanadium nanoparticles produced by means of a magnetron-based gas aggregation source. It is shown ...that while low magnetron currents and aggregation pressures lead to the formation of cubic vanadium nanoparticles, which is most likely connected with different kinetics growth modes on {100} and {110} surfaces of vanadium, higher magnetron currents and pressures result in the spherical-like but highly irregular morphology of produced NPs. Furthermore, it was found that the size of the nanoparticles may be adjusted by introducing He into the working gas mixture. An increase in the He partial pressure causes a substantial decrease in the size of nanoparticles but has no impact on their shape. This effect is predominately connected with the enhanced nucleation caused by He, which favours the production of a higher number of smaller nanoparticles. Finally, the vanadium nanoparticles, irrespective of their initial shape, may be transformed into fully spherical ones by introducing oxygen into the main deposition chamber, which is connected by their extensive heating during their in-flight oxidation.
•Morphology of V NPs produced by gas aggregation source can be controlled.•Low pressure/magnetron current conditions lead to the cubic shape of produced NPs.•Increasing pressure/magnetron current results in a near-spherical shape of V NPs.•Addition of He causes growth of smaller NPs but has no influence on their shape.•In-flight oxidation induces the transformation of V NPs into a spherical shape.
Nanoparticles composed of multiple silver cores and a plasma polymer shell (multicore@shell) were prepared in a single step with a gas aggregation cluster source operating with ...Ar/hexamethyldisiloxane mixtures and optionally oxygen. The size distribution of the metal inclusions as well as the chemical composition and the thickness of the shells were found to be controlled by the composition of the working gas mixture. Shell matrices ranging from organosilicon plasma polymer to nearly stoichiometric SiO
were obtained. The method allows facile fabrication of multicore@shell nanoparticles with tailored functional properties, as demonstrated here with the optical response.
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