In this study, we investigated the atomic-level interaction between CO molecules and a well-ordered Mn3O4(001) thin film. The oxide film, initially grown on a single-crystal Au(111) substrate, was characterized using X-ray photoelectron spectroscopy (XPS) to determine its oxidation state. Further examination of the film structure through scanning transmission electron microscopy (STEM) and low-energy electron diffraction (LEED) revealed its growth orientation along the [001] direction, with three domains rotated by 60 degrees and aligned with the < 110 >(Au) directions. Notably, the termination of the film features a layer of Mn3+ cations covered with oxygen atoms. The study then focused on the interaction of the film with CO, employing infrared reflection absorption spectroscopy (IRAS) and temperature-programmed IRAS (TP-IRAS). The results unveiled two distinct IR peaks related to CO adsorption: one at 2140 cm(-1), signifying that CO molecules weakly adsorbed on the oxygen-terminated surface of Mn3+ cations, and another at 2105 cm(-1), indicative of CO molecules bound to Mn2+ cations at oxygen vacancies.

Thiram is a pesticide derived from sulfur that has a highly toxic and biologically active chemical molecule due to its ability to chelate polyvalent cations, being the second most used fungicide in agriculture. Due to its toxic effects, which include liver damage, neurotoxicity, infertility problems and bone and cartilaginous malformations, among others, the detection of this contaminant in water is essential. This research work describes the development of a new glassy carbon electrode modified with electrochemically reduced graphene oxide and zinc oxide nanosheets (GCE-ErGO-ZnO) to detect the presence of the pesticide thiram by electrochemical means. The GCE-ErGO-ZnO electrode was examined morphologically and chemically and analyzed by cyclic voltammetry in the presence of thiram. Electrochemical characterization demonstrated that GCE-ErGO-ZnO presents the highest electrocatalytic activity for thiram oxidation using ZnO nanosheets. Thiram was successfully identified by the square wave voltammetry method in Britton-Robinson buffer 0.1 mol·L−1, at pH = 5.0. The developed electrochemical sensor allows the quantification of thiram in the linear range 0.09–0.96 μg·mL−1, with a LOD of 1.3 ng·mL−1 and LOQ of 4.3 ng·mL−1, significantly lower than the maximum Brazilian and global concentration levels, demonstrating that this method has significant potential to be used in monitoring this pesticide in watercourses.

Main text The key comparison CCQM-K157 for the thickness measurement of HfO2 films was performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The aim of CCQM-K157 is to establish the measurement traceability and to ensure the equivalency in the measurement capability of national metrology institutes for the thickness measurement of HfO2 films. In this key comparison, the thicknesses of six HfO2 films with the nominal thickness range from 0.7 nm to 6 nm were compared by x-ray photoelectron spectroscopy (XPS), x-ray reflectometry (XRR), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE) and medium energy ion scattering spectrometry (MEIS). To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

In this study, we investigated MnO thin films grown on Cu(111) using a soft x-ray and UV based spectroscopy, low energy electron diffraction (LEED), scanning tunneling (STM) and scanning transmission electron microscopy (STEM). MnO thin film assumes (110) preferential plane orientation organized in different spatial domains to better adapt to Cu(111) surface and an in-plane/out-of-plane lattice parameter variation up to 11% with respect to bulk counterpart originating a sizeable XLD signal at Mn L2,3 edges. The formation of oxidized Cu region during the MnO thin film growth is not avoidable due to the copper reactivity to oxygen and at the interface the coexistence of MnO islands alternated with Cu2O regions was observed by STM. Mn 2p and Mn 3s core level photoemission line shapes present a slight change in multiplet peak relative intensity with respect bulk MnO counterpart due to the role of Cu substrate in the core level relaxation process. The photon energy dependent photoemission spectra of valence band discriminate the MnO states and indicate a weak influence of the substrate once the film thickness is reduced to 1 nm. These findings open new route in the tuning oxide thin film properties.

In this work, two commercial UHMWPE (ultra-high molecular weight polyethylene) resins used in orthopedics, GUR 1050 and GUR 1020, were evaluated through linear reciprocating dry friction tests. Average contact pressures (P) of 34 MPa and 50 MPa and sliding velocities (V) of 0.02 m/s and 0.10 m/s were selected to perform tests in four PV conditions. The friction coefficient (COF) with both resins was around 0.18 in average, without significant distinctions by PV; however, a distinction was seen in COF dispersion; it was in the range of 5%-19%, in dependence of the PV condition and resin type. COF with GUR 1020 was more disperse, and it was related to the vulnerability of the resin to undergoing dynamic changes in the intensity of adhesive (higher COF) or abrasive (lower COF) wear mechanisms. Both wear mechanisms are displayed simultaneously, but random changes in intensity may occur during the friction process. Such randomness was associated to the susceptibility to have the structure modified by friction, higher in GUR 1020 than GUR 1050. Concerning wear amount, contact pressure was the most influencing parameter on it. GUR 1020 performed more than 30% inferior than GUR 1050 under contact pressure higher than the yield strength of the material. Under pressures near the material strength, the wear level was in the range of surface roughness and both resins performed equal in average; however, in this case, the dispersion was systematically lower for GUR 1050, evidencing its better tribological stability. It was concluded that analyses on the dispersion of the tribological responses disclosed relevant information on stability related performance. Also, when procedural dependent properties, as such friction and wear, are considered as evaluation parameters, care must be taken to compare results from different tribosystems.

This paper describes the development of a glassy carbon electrode modified with electrochemically reduced graphene oxide and zinc oxide nanosheets in order to detect the presence of the pesticide thiram in water by electrochemical means. ZnO nanosheets were synthesized in a microwave reactor and characterized by scanning electron microscopy and EDS. The modified GCE-ErGO-ZnO electrode was analyzed using scanning electron microscopy, EDS and cyclic voltammetry. Thiram was successfully identified by using the square wave voltammetry method in a 5.0 pH Britton-Robinson buffer with a concentration of 0.1 mol.L-1. The limits for detection and quantification were 0.002 µg.mL-1 and 0.005 µg.mL-1, respectively. These values are significantly lower than the Brazilian and global maximum concentration levels, demonstrating that this method has a significant potential to be employed in monitoring the concentration of this pesticide in waterways.

Understanding the physical origin of core-level photoemission line shapes can offer valuable information about the chemical and physical properties of surfaces. For instance, in a large number of transition metals oxides, changes in the line shape allow the accurate determination of their oxidation states and cation site symmetry. Yet, despite this importance, experimental investigations on core-level shifts have been much neglected in recent years. In order to provide further evidence of the physical relevance, we have, in this contribution, introduced a new aspect of interior-, terrace- and edge- atom core-level binding energy shifts to describe monolayers of MnO(001) films grown on an Au(111) substrate. By this means we were able to distinguish the line shape contributions related to different types of atomic sites. We show that their relative intensities and energy shifts are able to provide information about the relative amount of under coordinated atoms on the surface and, thus give insights into their catalytic properties. Our findings reveal the importance of a detailed surface science characterization to provide the correct interpretation of distinct photoemission line shapes when considering thin film samples as well as nanostructures in general.

Rational synthesis and simple methodology for the purification of large (35-45 nm in lateral size) and flat (1.0-1.5 nm of height) nitrogen-doped graphene oxide quantum dots (GOQDs) are presented. The methodology allows robust metal-free and acid-free preparation of N-GOQDs with a yield of about 100% and includes hydrothermal treatment of graphene oxide with hydrogen peroxide and ammonia. It was demonstrated that macroscopic impurities can be separated from N-GOQD suspension by their coagulation with 0.9% NaCl solution. Redispersible in water and saline solutions, particles of N-GOQDs were characterized using tip-enhanced Raman spectroscopy (TERS), photoluminescent, XPS, and UV-VIS spectroscopies. The size and morphology of N-GOQDs were studied by dynamic light scattering, AFM, SEM, and TEM. The procedure proposed allows nitrogen-doped GOQDs to be obtained, having 60-51% of carbon, 34-45% of oxygen, and up to 7.2% of nitrogen. The N-GOQD particles obtained in two hours of synthesis contain only pyrrolic defects of the graphene core. The fraction of pyridine moieties grows with the time of synthesis, while the fraction of quaternary nitrogen declines. Application of TERS allows demonstration that the N-GOQDs consist of a graphene core with an average crystallite size of 9 nm and an average distance between nearest defects smaller than 3 nm. The cytotoxicity tests reveal high viability of the monkey epithelial kidney cells Vero in the presence of N-GOQDs in a concentration below 60 mg L-1. The N-GOQDs demonstrate green luminescence with an emission maximum at 505 nm and sedimentation stability in the cell culture medium.

In this work, we examined the structure of Mn3O4 (110) thin films. Generally, Mn3+ and Mn2+ cation ratios on manganese oxide surfaces are expected to contribute to the catalytic activity of Mn3O4. However, the thermodynamically stable Mn3O4 (hausmannite) surface structure is not fully understood. Therefore, we investigated Mn3O4 films on Cu(111) combining X-ray photoelectron spectroscopy, low energy electron diffraction, scanning transmission electron microscopy, and scanning tunneling microscopy. Our results suggest a termination layer of Mn3O4 (110) film with a fully oxidized Mn2+ layer for the topmost surface and Mn3+ cations at the interface with Cu(111). The Mn3O4 (110) surface undergoes lattice distortions that may affect its chemical and physical properties known to be relevant for surface reactivity.

This study evaluated the effect of hexamethyldisiloxane (HMDSO) plasma on the fabrics surface to produce masks. Samples of 400-thread count cotton fabric were used. The fabrics was covered with a layer of HMDSO employing plasma enhanced chemical vapor deposition. Optical Microscopy, helium ion beam microscopy (HIM) and atomic force microscopy (AFM) were used for topographic analysis. Fourier transformed infrared spectroscopy technique was used to analyze the chemical modifications on surface. The level of hydrophobicity was evaluated using contact angle measurements. To evaluate the effect of washing cycle on the plasma coating, a protocol proposed by the World Health Organization was used. All experiments were performed in triplicate. For the statistical analysis, the Mann–Whitney, Kruskal–Wallis and Dunn tests were used. AFM showed that, after HMDSO plasma coating, a layer of small granules agglomerated on the original surface of the fabric was visualized. The fabric, which initially had a 0° contact angle value, presented angles of 120° after the plasma coating. It was concluded that the use of cotton fabric coated with HMDSO plasma proved to be adequate for the manufacture of protective masks, since the coating made the surface hydrophobic and this property is maintained even after washing cycles.

Glycerol is a major byproduct obtained in the production of biodiesel, an important renewable fuel. The presence of free glycerol in fuel can have structural and performance consequences with respect to the engine, making fuel quality control important. The standard method to analyze glycerol in biodiesel is gas chromatography, a time-consuming and expensive technique. In this context, an electrode based on glassy carbon electrodes (GCEs) modified with reduced graphene oxide and core-shell gold@palladium nanoparticles was developed for the determination of glycerol in biodiesel. The free glycerol analysis was performed in the aqueous phase obtained by liquid–liquid extraction from a biodiesel sample. Cyclic voltammetry was chosen as the method for glycerol electrochemical analysis to regenerate active sites and promote greater sensor stability. The modified Au@Pd/rGO/GCE electrode showed an excellent performance, obtaining a linear range of 18.2 to 109 µmol L−1 with a correlation coefficient of 0.9895, limits of detection and quantification of 5.33 and 17.6 µmol L−1, respectively, high stability during 1000 cycles, and recovery values of 86% and 87% in the quantification of glycerol in biodiesel samples. The proposed method proved to be a great alternative for the analysis of glycerol in biodiesel, being a fast, sensitive, and low-cost technique due to its high stability and the use of small quantities of reagents.

Main text A pilot study for the thickness measurement of HfO2 films was performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The aim of this pilot study was to ensure the equivalency in the measurement capability of national metrology institutes for the thickness measurement of HfO2 films. In this pilot study, the thicknesses of six HfO2 films with nominal thickness from 1 nm to 4 nm were measured by X-ray Photoelectron Spectroscopy (XPS), X-ray Reflectometry(XRR), X-ray Fluorescence Analysis (XRF), Transmission Electron Spectroscopy (TEM), Spectroscopic Ellipsometry (SE) and Rutherford Backscattering Spectrometry (RBS). The reference thicknesses were determined by mutual calibration of a zero-offset method (Medium Energy Ion Scattering Spectroscopy (MEIS) of KRISS) and a method traceable to the length unit (the average thicknesses of three XRR data except the thinnest film). These reference thicknesses are traceable to the length unit because they are based on the traceability of XRR. For the thickness measurement by XPS, the effective attenuation length of Hf 4f electrons was determined. In the cases of XRR and TEM, the offset values were determined from a linear fitting between the reference thicknesses and the individual data by XRR and TEM. The amount of substance of HfO2, expressed as thickness of HfO2 films (in both linear and areal density units), was found to be a good subject for a CCQM key comparison. To reach the main text of this paper, click on Final Report. The final report has been peer-reviewed and approved for publication by the CCQM.

The role of plasmon resonance on the optical efficiency of nanoantennas for tip-enhanced Raman spectroscopy (TERS) is reviewed. Technical details on surface plasmon polaritons (SPP), localized surface plasmon resonance (LSPR), and the plasmon gap mode are provided. Nanotechnology engineering is necessary to adequate the nanoantenna's size, shape and composition to match resonance conditions with the exciting radiation source. Computational simulation guides the development of new types of plasmonic nanoantennas with different materials and morphologies, specially designed to reach target applications. An overview on a recently developed nanoantenna composed by a truncated micropyramidal body with a nanopyramid end is presented. The characteristic length L of the nanopyramid tip is dimensioned to fine-tune LSPR modes, giving rise to the so-called plasmon-tunable tip pyramid (PTTP). The plasmonic properties of this type of probe were investigated by electron energy loss spectroscopy and computational simulations, reveling that PTTPs act as monopole nanoantennas. TERS results obtained with the PTTPs demonstrate the achievement of unprecedent levels of field enhancement mediated by LSPR with excellent reproducibility rate.

Abstract An electrochemical sensor based on a modified glassy carbon electrode (GCE) with reduced graphene oxide and Ni-Au nanoparticles (Ni(OH)2/AuNp/rGO/GCE) was developed for the determination of ethylene glycol. The graphene oxide was reduced electrochemically at the electrode surface by chronoamperometry, the gold nanoparticles were deposited by chronopotentiometry while the nickel hydroxide nanoparticles were deposited by cyclic voltammetry. The characterization of graphene oxide was performed by Raman spectroscopy, X-ray diffraction (XRD) and transmission-mode scanning electron microscopy (TSEM), while the modified electrodes were characterized by scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) analysis. The determination of ethylene glycol was performed by cyclic voltammetry due to the regeneration of the active sites, preventing loss of the sensor signal. The modified GCE with rGO and Ni(OH)2/AuNp showed a good performance obtaining a linear range of 0.24 to 1.4 mmol L-1 with a correlation coefficient of 0.9903, limits of detection and quantification (49 and 162 µmol L-1, respectively) and high stability with 500 continuous analysis cycles.

The projections for the global energy demand have been one of our society's greatest challenges, which has contributed significantly to the search for new sources of energy, among which biodiesel stands out and, consequently, the development of methods for quality assurance is essential to ensure its technological demand. In this context, a stable sensor based on graphene oxide and gold nanoparticles was developed for glycerol analysis. The electrochemically deposited gold nanoparticles presented the best results with a peak current (I-p) four times greater than the chemically produced gold nanoparticles. The combination of glassy carbon electrode with electrochemically reduced graphene and electrochemically deposited gold nanoparticles (GCE-ErGO-EAuNp) resulted in an efficient sensor to detect glycerol, promoting an I-p increase. The proposed non-enzymatic method showed a linear response in the concentration range of 1.0 x 10(-3) to 1.0 x 10(-2%)(w/w) with a good determination coefficient (r(2) = 0.9989), limits of detection and quantification at 1.2 x 10(-4%) and 4.0 x 10(-4%) (w/w), respectively, with a repeatability of (RSD% ranged from 0.36% to 2.78%), intermediate precision and recovery of (99.3% to 104.4%) and excellent stability of 700 continuous analysis cycles.

The Cu/a-Si:H system has been studied by gas effusion method, elastic recoil detection analysis (ERDA), in situ sheet resistance measurements and scanning electron microscopy. Cu layers of 15 and 90 nm in thickness were deposited by e-beam evaporation onto 1 µm a-Si:H films produced by RF glow discharge on Si(100) substrates at 250 °C. The most important effects are observed in the effusion measurements, when pure a-Si:H samples and Cu/a-Si:H samples are compared. For the Cu/a-Si:H samples, three well-defined peaks are observed, one at very low temperature (T=200 °C), another at 380 °C and a high temperature peak at about. However, pure a-Si:H shows only one effusion maxima at 550 °C. The low temperature effusion peaks are directly correlated with steps increases in the sheet resistance measurements. The first one (T=200 °C) is due to the beginning of silicide formation. The H2 evolution at 380 °C is correlated to phase transition in the a-Si:H film. The hydrogen depth profiles obtained by ERDA and SEM observations are also used to describe the aspects of the Cu/a-Si:H interaction.

Plasmon-tunable tip pyramids (PTTPs) are reproducible and efficient nanoantennas for tip-enhanced Raman spectroscopy (TERS). Their fabrication method is based on template stripping of a segmented gold pyramid with a size-adjustable nanopyramid end, which is capable of supporting monopole localized surface plasmon resonance (LSPR) modes leading to high spectral enhancement when its resonance energy is matched with the excitation laser energy. Here, we describe in detail the PTTP fabrication method and report a statistical analysis based on 530 PTTPs' and 185 ordinary gold micropyramids' templates. Our results indicate that the PTTP method generates probes with an apex diameter smaller than 30 nm on 92.4% of the batch, which is a parameter directly related to the achievable TERS spatial resolution. Moreover, the PTTPs' nanopyramid edge size L, a critical parameter for LSPR spectral tuning, shows variability typically smaller than 12.5%. The PTTP's performance was tested in TERS experiments performed on graphene, and the results show a spectral enhancement of up to 72-fold, which is at least one order of magnitude higher than that typically achieved with gold micropyramids. Imaging resolution is in the order of 20 nm.

The corn-starch was able to reduce Pd(II) species under relatively low concentration (5.0 wt/vol) leading to the formation of a thermoresponsive palladium nanoparticles-containing hydrogel with D = 16.1 nm ± 6.4 nm. It was successfully applied to the Suzuki–Miyaura reaction step in neat water involved in the synthesis of (±)-N-acetyl-α-methyl-4-biphenylalanine ethyl ester, a direct precursor of an unnatural quaternary biarylalanine.

Organic light-emitting diode (OLED) devices in the archetype small-molecule fluorescent guest-host system tris(8-hydroxyquinolinato) aluminum ($\mathrm{Al}{\mathrm{q}}_{3}$) doped with 4-(dicyanomethylene)-2-methyl-6-julolidyl-9-enyl-4H-pyran (DCM2) displays a redshift in light-emission frequency which is extremely sensitive to the dopant concentration. This effect can be used to tune the emission frequency in this particular class of OLEDs. In this work, a model is proposed to describe this effect using a combination of density functional theory quantum-chemical calculations and stochastic simulations of exciton diffusion via a F\"orster mechanism. The results show that the permanent dipole moments of the $\mathrm{Al}{\mathrm{q}}_{3}$ molecules generate random electric fields that are large enough to cause a nonlinear Stark shift in the band gap of neighboring DCM2 molecules. As a consequence of these nonlinear shifts, a non-Gaussian probability distribution of highest occupied molecular orbital to lowest unoccupied molecular orbital (HOMO-LUMO) gaps for the DCM2 molecules in the $\mathrm{Al}{\mathrm{q}}_{3}$ matrix is observed, with long exponential tails to the low-energy side. Surprisingly, this probability distribution of DCM2 HOMO-LUMO gaps is virtually independent of DCM2 concentration into the $\mathrm{Al}{\mathrm{q}}_{3}$ matrix, at least up to a fraction of 10%. This study shows that this distribution of gaps, combined with out-of-equilibrium exciton diffusion among DCM2 molecules, is sufficient to explain the experimentally observed emission redshift.