Thickness dependence of the room-temperature ethanol sensor properties of Cu2O polycrystalline films.

This study investigates the fabrication process of copper thin films via thermal evaporation, with precise control over film thickness achieved throughZ-position adjustment. Analysis of the as-fabricated copper films reveals a discernible relationship between grain size (〈D〉) andZ-position, characterized by a phenomenological equation〈D〉XRDn(Z)=〈D〉0n1+32rZ2+158rZ4, which is further supported by a growth exponent (n) of 0.41 obtained from the analysis. This value aligns well with findings in the literature concerning the growth of copper films, thus underlining the validity and reliability of our experimental outcomes. The resulting crystallites, ranging in size from 20 to 26 nm, exhibit a resistivity within the range of 3.3-4.6µΩ · cm. Upon thermal annealing at 200 °C, cuprite Cu2O thin films are produced, demonstrating crystallite sizes ranging from ∼9 to ∼24 nm with increasing film thickness. The observed monotonic reduction in Cu2O crystallites relative to film thickness is attributed to a recrystallization process, indicating amorphization when oxygen atoms are introduced, followed by the nucleation and growth of newly formed copper oxide phase. Changes in the optical bandgap of the Cu2O films, ranging from 2.31 to 2.07 eV, are attributed mainly to the quantum confinement effect, particularly important in Cu2O with size close than the Bohr exciton diameter (5 nm) of the Cu2O. Additionally, correlations between refractive index and extinction coefficient with film thickness are observed, notably a linear relationship between refractive index and charge carrier density. Electrical measurements confirm the presence of a p-type semiconductor with carrier concentrations of ∼1014cm-3, showing a slight decrease with film thickness. This phenomenon is likely attributed to escalating film roughness, which introduces supplementary scattering mechanisms for charge carriers, leading to a resistivity increase, especially as the roughness approaches or surpasses the mean free path of charge carriers (8.61 nm). Moreover,ab-initiocalculations on the Cu2O crystalline phase to investigate the impact of hydrostatic strain on its electronic and optical properties was conducted. We believe that our findings provide crucial insights that support the elucidation of the experimental results. Notably, thinner cuprite films exhibit heightened sensitivity to ethanol gas at room temperature, indicating potential for highly responsive gas sensors, particularly for ethanol breath testing, with significant implications for portable device applications.

Iron oxide nanostructured electrodes for detection of copper(II) ions.

Iron oxide nanostructured (ION) electrodes were assembled layer-by-layer onto ITO-coated glass substrates and their structure, morphology, and electrochemical properties were investigated, the latter aiming at the development of a chemical sensor for Cu2+. The electrodes were built by immersing the substrate alternately into an aqueous colloidal suspension of positively charged magnetite nanoparticles (np-Fe3O4, 8 nm) and an aqueous solution of anionic sodium sulfonated polystyrene (PSS). The adsorbed amount of both materials was monitored ex-situ by UV-vis spectroscopy and it was found to increase linearly with the number of deposition cycles. The resulting films feature a densely-packed structure of magnetite nanoparticles, as suggested by AFM and Raman spectroscopy, respectively. Cyclic voltammograms of electrodes immersed in acetate buffer (pH 4.6) displayed three electrochemical events that were tentatively ascribed to the reduction of Fe(III) oxy-hydroxide to magnetite, reduction of maghemite to magnetite, and finally oxidation of magnetite to maghemite. The effect of np-Fe3O4/PSS bilayers on the ION electrode performance was to increase the anodic and cathodic currents produced during electrochemical oxidation-reduction of the Fe(CN)(3-/4-) redox couple. With more bilayers, the ION electrode provided higher anodic/cathodic currents. Moreover, the redox couple exhibited a quasi-reversible behavior at the ION electrode as already observed with other working electrode systems. Fitting of voltammetry data provided the apparent electron transfer constants, which were found to be higher in ION electrodes for both redox couples (Fe(CN)(3-/4-) and Cu(2+/0)). By means of differential pulsed anodic stripping voltammetry, the ION electrodes were found to respond linearly to the presence of Cu2+ in aqueous samples in the range between 1.0 and 8.0 x 10(-6) mol x L(-1) and displayed a limit of detection of 0.3 x 10(-8) mol x L(-1). The sensitivity was - 0.6µA/µmol x L(-1). In standard addition and recovery experiments performed with tap water the recovery was about 102%-119%. In similar experiments conducted with ground and instant coffee samples the recovery was 92.5% and 103%, respectively. Furthermore, the ION electrodes were almost insensitive to the presence of common interfering ions, such as Zn2+, Mn2+, Ni2+, and Fe3+, even at concentrations ten times higher than that of Cu2+.

Cu-doped SnO2 nanoparticles: size and antibacterial activity investigations.

Nowadays, the use of self-cleaning surfaces is increasing globally, especially after the COVID-2019 pandemic, and the use of nanoparticles has been shown as a plausible option for this purpose. In the present study, Cu-doped SnO2 nanocrystals were successfully synthesized (in the copper content range of 0-30 mol%) using the polymeric precursor method. The structural, morphological, vibrational, and antibacterial activity were carefully studied to unveil the effect of copper ions on the properties of the hosting matrix, aiming at maximizing the usage of Cu-doped SnO2 nanocrystals. The results show fabrication of nanoparticles near their respective exciton Bohr diameter (5.4 nm for SnO2), however, monophasic SnO2 was observed up to 15 mol%. Above this limit, a secondary CuO phase was observed, as shown by the assessed X-ray diffraction (XRD), Fourier transform infrared, and Raman spectroscopy data. Furthermore, the redshift of the primary A1g vibrational mode of SnO2 is successfully described using the phonon-confinement model, demonstrating a good relationship between the Raman correlation length (L) and the crystallite size (〈D〉), the latter determined from XRD. Regarding the antibacterial activity, assessed via the disc-diffusion testing method (DDTM) while challenging two bacterial species (S. aureus and E. coli), our results suggest a rapid diffusion of the nanoparticles out of the paper disc, with a synergistic effect credited to the Sn1-xCuxO2-CuO phases contributing to the inhibition of the bacteria growth. Moreover, the DDTM data scales with cell viability, the latter analyzed using the Hill equation, from which both lethal dose 50 (LD50) and benchmark dose (BMD) were extracted.

Temperature-dependent Raman study of thermal parameters in CdS quantum dots.

We report on the strong temperature-dependent thermal expansion, α(D), in CdS quantum dots (QDs) embedded in a glass template. We have performed a systematic study by using the temperature-dependent first-order Raman spectra, in CdS bulk and in dot samples, in order to assess the size dependence of α(D), and where the role of the compressive strain provoked by the glass host matrix on the dot response is discussed. We report the Grüneisen mode parameters and the anharmonic coupling constants for small CdS dots with mean radius R âˆ¼ 2.0 nm. We found that γ parameters change, with respect to the bulk CdS, in a range between 20 and 50%, while the anharmonicity contribution from two-phonon decay channel becomes the most important process to the temperature-shift properties.

Biocompatible magnetic microspheres for Use in PDT and hyperthermia.

Loaded microspheres with a silicon (IV) phthalocyanine derivative (NzPC) acting as a photosensitizer were prepared from polyhydroxybutyrate-co-valerate (PHBHV) and poly(ecaprolactone) (PCL) polymers using the emulsification solvent evaporation method (EE). The aim of our study was to prepare two systems of these biodegradable PHBHV/PCL microspheres. The first one containing only photosensitizer previously incorporated in the PHBHV and poly(ecaprolactone) (PCL) microspheres and the second one with the post magnetization of the DDS with magnetic nanoparticles. Magnetic fluid is successfully used for controlled incorporation of nanosized magnetic particles within the micron-sized template. This is the first time that we could get a successful pos incorporation of nanosized magnetic particles in a previously-prepared polymeric template. This procedure opens a great number of possibilities of post-functionalization of polymeric micro or nanoparticles with different bioactive materials. The NzPC release profile of the systems is ideal for PDT, the zeta potential and the size particle are stable upon aging in time. In vitro studies were evaluated using gingival fibroblastic cell line. The dark citotoxicity, the phototoxicity and the AC magnetic field assays of the as-prepared nanomagnetic composite were evaluated and the cellular viability analyzed by the classical test of MTT.

Investigation of colloidal stability and insulation characteristics of magnetic oils.

Superparamagnetic iron-oxide (SPIO) particles were synthesized by the co-precipitation method and the oleic acid-coated SPIO (OA-SPIO) was then obtained by a surface grafting procedure. A stock sample of magnetic oil (MO) with 1.6% particle volume fraction (VF) was obtained by dispersing the OA-SPIO in insulating naphthenic oil. The MO stock sample was diluted in the same naphthenic oil to yield MO with 0.1, 0.04, 0.02, and 0.01% VF. Moreover, the 0.04% VF MO sample was manipulated to yield MO samples with water content of 26, 37, and 63 mg L(-1). The spinel structure of OA-SPIO was assessed by XRD and the average diameter of 8.3 nm was provided by TEM analysis. The saturation magnetization at room temperature (RT) was 70 emu/g and no remanence or coercivity was observed. The average hydrodynamic diameter (D(H)) of the colloidal particles suspended within the 0.04% VF MO sample was 58 nm. After aging for 30 days at RT no change was observed for the lowest water content MO sample (26 mg L(-1)). However, D(H) equals to 270 nm was observed for the highest water content MO sample (63 mg L(-1)). The MO samples with 26 mg L(-1) water content were found stable under heating at 90 degrees C for all VF investigated. We found the insulation resistance dropping significantly as VF and temperature increases. The lowest value found was 11 GOhms for the 0.1% VF at 60 degrees C, which is an acceptable value for MO.

New magnetic fluid developed with natural organic compounds biocompatible.

This work was developed with an aqueous suspension of maghemite nanoparticles and colloidal emulsions with nanoparticles of magnetite. The nanoparticles were synthesized by co-precipitation method. The first was the magnetic emulsion nanoparticles of maghemite dispersed in the aqueous extract obtained from the leaf embauba (Cecropia Obtusifolia), whose tree is native to Central and South America. Thereby achieving the magnetic fluid extract embauba stabilized with ionic buffer solution pH 7.4. A second emulsion was prepared with colloidal magnetite nanoparticles with surfaces previously coated with oleic acid as a means of dispersing and using the oil extracted from in nature seed Andiroba (Carapa Guianensis), tree of the Brazilian Amazon. These new magnetic fluids the nanoparticles were characterized by Photoacoustic spectroscopy (PAS) to determine the coating layer of molecules on the surfaces of nanoparticles. In aqueous ionic magnetic fluid Cecropia Obtusifolia (MFCO) chlorogenic acid contributes to the electron density in the presence of four groups alcohols, a ketone group and a carboxylic group. In magnetic fluid-based oil andiroba MFAD PAS spectra show that oleic acid molecules are tightly linked on the surface of the nanoparticles.

Tailoring magnetic nanoparticle for transformers application.

In this study photoacoustic spectroscopy was used to investigate the effect of dilution of an oil-based magnetic fluid sample on the magnetic nanoparticle surface-coating. Changes of the photoacoustic signal intensity on the band-L region (640 to 830 nm) upon dilution of the stock magnetic fluid sample were discussed in terms of molecular surface desorption. The model proposed here assumes that the driving force taking the molecules out from the nanoparticle surface into the bulk solvent is the gradient of osmotic pressure. This gradient of osmotic pressure is established between the nanoparticle surface and the bulk suspension. It is further assumed that the photoacoustic signal intensity (area under the photoacoustic spectra) scales linearly with the number of coating molecules (surface grafting) at the nanoparticle surface. This model picture provides a non-linear analytical description for the reduction of the surface grafting coefficient upon dilution, which was successfully-used to curve-fit the photoacoustic experimental data.

Carrier transport investigation in short-wavelength InAs/AlGaAs quantum dots.

Spatially resolved photoluminescence has been used to investigate the details of the carrier capture and recombination dynamics in InAs/AlGaAs self-assembled quantum dots. The spatial PL distribution displays a Gaussian-like profile, whose width depends upon the temperature and detection energy being analyzed. The results give evidence of carrier thermalization between dots with different sizes. The effects of carrier transport in the quantum dot (QD) structure and carrier capture cannot be separated. The results can be modeled by assuming a carrier hopping process.

Dynamic susceptibility investigation of maghemite nanoparticles incorporated in bovine serum albumin template.

Room-temperature measurements of the magnetic susceptibility of Bovine Serum Albumin-based nanocapsules (50 to 300 nm in size) loaded with different amounts of maghemite nanoparticles (7.6 nm average diameter) have been carried out in this study. The field (H) dependence of the imaginary peak susceptibility (fp) of the nanocomposite samples was investigated in the range of 0 to 4 kOe. From the analysis of the fp x H curves the concentration (N) dependence of the effective maghemite magnetocrystalline energy barrier (E) was obtained. Analysis of the E x N data was performed using a modified Mørup-Tronc [Phys. Rev. Lett. 72, 3278 (1994)] model, from which a huge contribution from the magnetocrystalline surface anisotropy was observed.

Evaluation of the binding properties of maghemite nanoparticle surface-coated with meso-2-3-dimercaptosuccinic acid to serum albumin.

In this study the interaction between magnetic nanoparticles (MNPs) surface-coated with meso-2,3-dimercaptosuccinic acid (DMSA) with both bovine serum albumin (BSA) and human serum albumin (HSA) was investigated. The binding of the MNP-DMSA was probed by the fluorescence quenching of the BSA and HSA tryptophan residue. Magnetic resonance and light microscopy analyses were carried out in in vivo tests using female Swiss mice. The binding constants (Kb) and the complex stoichiometries (n) indicate that MNP-DMSA/BSA and MNP-DMSA/HSA complexes have low association profiles. After five minutes following intravenous injection of MNP-DMSA into mice's blood stream we found the lung firstly target by the MNP-DMSA, followed by the liver in a latter stage. This finding suggests that the nanoparticle's DMSA-coating process probably hides the thiol group, through which albumin usually binds. This indicates that biocompatible MNP-DMSA is a very promising material system to be used as a drug delivery system (DDS), primarily for lung cancer treatment.

Role of surfactant molecules in magnetic fluid: comparison of Monte Carlo simulation and electron magnetic resonance.

We investigate a magnetic fluid composed of magnetite nanoparticles surfacted with dodecanoic acid molecules and stably dispersed in a hydrocarbon solvent. A comparison between Monte Carlo simulation and different experimental techniques allows us to validate our methodology and investigate the behavior of the surfactant molecules. Our analysis, based on the Langmuir model, suggests that the surfactant grafting number on isolate nanoparticles increases with the nanoparticle concentration, while the grafting on agglomerated nanoparticles presents a more complicated behavior. Our results suggests that, if properly coated and at a certain concentration range, colloids can become stable even in the presence of agglomerates. The role of the Hamaker constant, which controls the van der Waals interaction intensity, was also investigated. We have found that the ratio between grafting and Hamaker constant governs the level of nanoparticle agglomeration.

SERS Investigation of Cancer Cells Treated with PDT: Quantification of Cell Survival and Follow-up.

In this study Surface Enhanced Raman Spectroscopy (SERS) data recorded from mouse mammary glands cancer cells (4T1 cell line) was used to assess information regarding differences between control, death and viable cells after Photodynamic Therapy (PDT) treatment. The treatment used nanoemulsions (NE/PS) loaded with different chloroaluminumphthalocyanine (ClAlP) photosensitizer (PS) contents (5 and 10 µmol × L-1) and illumination (660 nm wavelength) at 10 J × cm-2 (10 minutes). The SERS data revealed significant molecular alterations in proteins and lipids due to the PDT treatment. Principal Component Analysis (PCA) was applied to analyze the data recorded. Three-dimensional and well reproductive PCA scatter plots were obtained, revealing that two clusters of dead cells were well separated from one another and from control cluster. Overlap between two clusters of viable cells was observed, though well separated from control cluster. Moreover, the data analysis also pointed out necrosis as the main cell death mechanism induced by the PDT, in agreement with the literature. Finally, Raman modes peaking at 608 cm-1 (proteins) and 1231 cm-1 (lipids) can be selected for follow up of survival rate of neoplastic cells after PDT. We envisage that this finding is key to contribute to a quick development of quantitative infrared thermography imaging.

Structural and magnetic properties of core-shell Au/Fe3O4 nanoparticles.

We present a systematic study of core-shell Au/Fe3O4 nanoparticles produced by thermal decomposition under mild conditions. The morphology and crystal structure of the nanoparticles revealed the presence of Au core of d = (6.9 ± 1.0) nm surrounded by Fe3O4 shell with a thickness of ~3.5 nm, epitaxially grown onto the Au core surface. The Au/Fe3O4 core-shell structure was demonstrated by high angle annular dark field scanning transmission electron microscopy analysis. The magnetite shell grown on top of the Au nanoparticle displayed a thermal blocking state at temperatures below TB = 59 K and a relaxed state well above TB. Remarkably, an exchange bias effect was observed when cooling down the samples below room temperature under an external magnetic field. Moreover, the exchange bias field (HEX) started to appear at T~40 K and its value increased by decreasing the temperature. This effect has been assigned to the interaction of spins located in the magnetically disordered regions (in the inner and outer surface of the Fe3O4 shell) and spins located in the ordered region of the Fe3O4 shell.

Cell toxicity studies of albumin-based nanosized magnetic beads.

The aim of this study was to prepare bovine serum albumin-based beads containing maghemite nanoparticles incorporated via ionic magnetic fluid and to evaluate the cell toxicity of this biocompatible system using the J774-A1 cell line. Transmission electron micrographs obtained from the magnetic fluid sample were used to estimate the average particle diameter around 7.6 nm and diameter dispersion of 0.22. The BSA-based magnetic beads were prepared using the heat protein denaturation route. The nanoparticle concentration in the magnetic fluid sample used for the synthesis of the magnetic beads was in the range of 1.2 x 10(16) to 2.3 x 10(17) particle/ml. The methodology used to investigate the cell toxicity of the magnetic beads was the classical MTT assay. Our observation showed that the toxicity against the J774-A1 cell line depends upon the amount of magnetic material incorporated into the magnetic nanobeads and was found to be 14, 11, 9, 5, and 3% for 2.3 x 10(17), 1.2 x 10(17), 4.6 x 10(16), 2.3 x 10(16), and 1.2 x 10(16) particle/ml, respectively.

Study of Iron oxide nanoparticles using Mössbauer spectroscopy with a high velocity resolution.

Iron oxide (magnetite and maghemite) nanoparticles developed for magnetic fluids were studied using Mössbauer spectroscopy with a high velocity resolution at 295 and 90K. The recorded Mössbauer spectra have demonstrated that usual physical models based on octahedral and tetrahedral sites were not suitable for fitting. Alternatively, the Mössbauer spectra were nicely fitted using a large number of magnetic sextets. The obtained results showed that the Mössbauer spectra and the assessed parameters were different for nanoparticles as-prepared and dispersed in the dispersing fluid at 295K. We claim that this finding is mainly due to the interaction of polar molecules with Iron cations at nanoparticle's surface or due to the surface coating using carboxylic-terminated molecules. It is assumed that the large number of spectral components may be related to complexity of the nanoparticle's characteristics and deviations from stoichiometry, including in the latter the influence of the oxidation of magnetite towards maghemite.

Investigation of ferromagnetic resonance and magnetoresistance in anti-spin ice structures.

In this work, we report experimental and theoretical investigations performed in anti-spin ice structures, composed by square lattice of elongated antidots, patterned in nickel thin film. The magnetic vortex crystal state was obtained by micromagnetic simulation as the ground state magnetization, which arises due to the magnetic stray field at the antidot edges inducing chirality in the magnetization of platters among antidots. Ferromagnetic resonance (FMR) and magnetoresistance (MR) measurements were utilized to investigate the vortex crystal magnetization dynamics and magnetoelectric response. By using FMR, it was possible to detect the spin wave modes and vortex crystal resonance, in good agreement with dynamic micromagnetic simulation results. The vortex crystal magnetization configuration and its response to the external magnetic field, were used to explain the isotropic MR behaviour observed.

Evolution of the doping regimes in the Al-doped SnO2 nanoparticles prepared by a polymer precursor method.

In this study, we report on the structural and hyperfine properties of Al-doped SnO2 nanoparticles synthesized by a polymer precursor method. The x-ray diffraction data analysis carried out using the Rietveld refinement method shows the formation of only rutile-type structures in all samples, with decreasing of the mean crystallite size as the Al content. A systematic study of the unit cell, as well as the vicinity of the interstitial position show strong evidence of two doping regimes in the rutile-type structure of SnO2. Below 7.5 mol% doping a dominant substitutional solution of Al(+3) and Sn(4+)-ions is determined. However, the occupation of both substitutional and interstitial sites is determined above 7.5 mol% doping. These findings are in good agreement with theoretical ab initio calculations.

Raman spectroscopy in magnetic fluids.

In this work Raman spectroscopy was used to investigate uncoated magnetic fluids (UMF's) and coated magnetic fluids (CMF's). The coating agents were N-oleoylsarcosine, dodecanoic acid, and ethoxylated polyalcohol. The Raman probe is the hydroxyl (OH) group chemisorbed at the magnetic nanoparticle surface and the measurements were performed in the typical OH bending and OH stretching regions. The room temperature Raman data obtained from the UMF's and CMF's are compared to each other and with the data obtained from liquid water. Suppression of Raman modes from the MF's are discussed in terms of symmetry reduction and in terms of the interaction between the chemisorbed OH-group and the surrounding medium. The relative grafting coefficient associated to different coatings are estimated from the Raman data. The highest grafting coefficient is achieved with a single coating of dodecanoic acid in the hydrocarbon-based MF. The surface-grafting coefficient of the N-oleoylsarcosine-coated MF reduces when the polar liquid carrier replaces the non-polar liquid carrier. In comparison to liquid water, it was found that the hydrogen bonding between the chemisorbed OH-group and the solvent was enhanced in UMF's and reduced in CMF's.

Comparative study of iron oxide nanoparticles as-prepared and dispersed in Copaiba oil using Mössbauer spectroscopy with low and high velocity resolution.

Iron oxide nanoparticles, probably magnetite, as-prepared and dispersed in Copaiba oil were studied by Mössbauer spectroscopy using two different spectrometers: with a low velocity resolution (512 channels) for measurements at 295 and 21K and with a high velocity resolution (4096 channels) for measurements at 295 and 90K. The fitting of all measured spectra demonstrated that usual models applied to fit Mössbauer spectra of magnetite and maghemite particles were not suitable. Therefore, the recorded spectra were fitted using a large number of spectral components on the basis of better quality of the fit and linearity of differential spectra. The number of components obtained for the better fit appeared to be different for spectra measured with a low and a high velocity resolution. However, these results demonstrated differences of Mössbauer parameters for iron oxide nanoparticles as-prepared and dispersed in Copaiba oil at applied temperatures. The effect of Copaiba oil molecules on Mössbauer parameters may be a result of the interactions of polar molecules such as kaurinic acid with nanoparticles' surface.