XPS

We investigated the mechanism of enzyme immobilization on silanized surfaces through coupling agents (cross-linkers) in order to understand the role of these molecules on interfacial processes and their eff ect on catalytic activity. To this end, we used a model multimeric enzyme (G6PDH) and several cross-linking molecules with diff erent chemical properties, including the nature of the end-group (-NCO, -NCS, -CHO), the connecting chain (aliphatic vs aromatic), and geometrical constraints (meta vs paradisubstituted aromatics). There did not seem to be radical diff erences in the mechanism of enzyme adsorption according to the linker used as judged from QCM-D, except that in the case of DIC (1,4-phenylene diisocyanate) the adsorption occurred more rapidly. In contrast, the nature of the cross-linker exerted a strong infl uence on the amount of enzyme immobilized as estimated from XPS, and more unexpectedly on the stability of the underlying silane layer. DIC, PDC (1,4-phenylene diisothiocyanate), or GA (glutaraldehyde) allowed successful enzyme immobilization. When the geometry of the linker was changed from 1,4-phenylene diisothiocyanate to 1,3-phenylene diisothiocyanate (MDC), the silane layer was subjected to degradation, upon enzyme adsorption, and the amount of immobilized molecules was signifi cantly lowered. TE (terephtalaldehyde) and direct enzyme deposition without cross-linker were similar to MDC. The organization of immobilized enzymes also depended on the immobilization procedure, as diff erent degrees of aggregation were observed by AFM. A correlation between the size of the aggregates and the catalytic properties of the enzyme was established, suggesting that aggregation may enhance the thermostability of the multimeric enzyme, probably through a compaction of the 3D structure.

Original scientific paper In the paper there is described the AISI 316L stainless steel surface obtained after electrochemical treatment in concentrated HNO3. It was characterized by roughness parameters, corrosion protection behaviour and chemical composition of the surface layer. Generally used 2D and 3D roughness parameters describing the surface after the electrochemical treatment are the following: Ra = 0.737 µm and Sa = 1,13 µm as well as Rq = 0,895 µm and Sq = 1,37 µm. In case of corrosion studies the passive current density was equal to 2,3×10 ̶ 2 µA/cm2, pitting potential was equal to Epit = 1140 mV vs. SCE and re-passivation potential was 79 mV vs. SCE. In the surface layer there were detected compounds of iron, chromium, molybdenum, cobalt, manganese, as well as calcium (contamination). The high resolution XPS spectra/results data have shown that most of detected iron compounds can be described as Fe2O3/FeOOH and chromium compounds as Cr2O3/CrOOH. The molybdenum detected ...

A novel solid acid nano-catalyst [Ti(SO4)O] was synthesised and used for the simultaneous esterification and transesterification of free fatty acids in used cooking oil (UCO) to produce biodiesel. The synthesised nano-catalyst was fully characterised by different analytical techniques. The XPS results clearly confirmed that the bidentate sulphate coordinated to the Ti4+ metal in the nano-catalyst product. Obtained d-spacing values from the experimental data of XRD peaks and the SAED pattern of produced nano-catalyst agreed well with the d-spacing values from the JCPDS-ICDD card numbers 04-011-4951 for titanium sulphate oxide or titanium oxysulfate crystal structures.This confirms the sulphate groups were within the crystalline structure rather than on the surface of titania nanoparticles, which has not been previously reported. It has been demonstrated 97.1% yield for the fatty acid methyl ester can be achieved usign the synthetised catalyst under a reaction time of 3 hrs, catalyst ...

MnMoW-triple oxide catalyst for chlorine-less oxygen generating electrodes from seawater electrolysis were prepared by repeated anodic deposition of their oxides on Ti/IrO2 substrate. The durability of the electrodes were examined by electrolysis in 0.5 M NaCl solution at current density of 1000 Am−2 and compared with their corresponding electrodes that were prepared by continuous anodic deposition. The electrodes repeatedly and continuously deposited for 90 min kept the oxygen evolution efficiency higher than 99% for 2600 h and 120 h of electrolysis, respectively. The improvement in the electrode durability by repeated deposition was attributed to the formation of single phase oxide deposits of MnMoW-oxides with optimized thickness, composition and structural water content, which enables the reduction of the electrode overpotential for the oxygen evolution reaction and increase overall stability and adhesion of the oxide deposits to Ti/IrO2 substrate. A mechanism for oxygen evolution at the anode surface during electrolysis was proposed.► MnMoW-oxides developed as new anodes for oxygen evolution during seawater electrolysis. ► Repetition of anodic deposition extended the durability of the anodes. ► The high durability attributed to the formation of a single phase triple oxide.

This paper reports on the wettability and aging behaviors of the silicon wafers that had been cleaned using a piranha (3:1 mixture of sulfuric acid (H 2 SO 4 , 96%) and hydrogen peroxide (H 2 O 2 , 30%), 120 1C), SC1 (1:1:5 mixture of NH 4 OH, H 2 O 2 and H 2 O, at 80 1C) or HF solution (6 parts of 40% NH 4 F and 1 part of 49% HF, at room temperature) solution, and treated with gaseous plasma. The silicon wafers cleaned using the piranha or SC1 solution were hydrophilic, and the water contact angles on the surfaces would increase along with aging time, until they reached the saturated points of around 701. The contact angle increase rate of these wafers in a vacuum was much faster than that in the open air, because of loss of water, which was physically adsorbed on the wafer surfaces. The silicon wafers cleaned with the HF solution were hydrophobic. Their contact angle decreased in the atmosphere, while it increased in the vacuum up to 951. Gold thin films deposited on the hydrophilic wafers were smoother than that deposited on the hydrophobic wafers, because the numerous oxygen groups formed on the hydrophilic surfaces would react with gold adatoms in the sputtering process to form a continuous thin film at the nucleation stage. The argon, nitrogen, oxygen gas plasma treatments could change the silicon wafer surfaces from hydrophobic to hydrophilic by creating a thin (around 2.5 nm) silicon dioxide film, which could be utilized to improve the roughness and adhesion of the gold thin film.

The atomic surface structure of SrTiO3(100) after annealing at 630 °C in vacuum is investigated by x-ray photoelectron diffraction (XPD) using the Sr 3d5/2 core level. The photoelectron diffraction peaks are successfully assigned by considering the forward scattering of photoelectrons by the atomic potential near the emitter atom in the lattice. The strongest diffraction peaks are aligned along the single crystal internuclear axes. We compare the results of photoelectron multiple scattering calculations (MSC) of SrO and TiO2 terminated SrTiO3(100) surfaces, including surface relaxation and rumpling, with the experimental data. For TiO2 and SrO terminated SrTiO3(100) surfaces, all top-layer cations relax inward, whereas second-layer atoms relax outward. The surface rumpling for SrO- and TiO2-terminated surfaces agrees well with low-energy electron diffraction results. Using a genetic algorithm the best agreement of MSC to the experimental XPD data is obtained for a SrO terminated surface with a 30% coverage of 3 ML SrO(100) islands.

Resumen: En este artículo se realiza una introducción a la espectroscopia
fotoelectrónica de Rayos X (XPS) que es la técnica de análisis más utilizada en la
caracterización química de la superficie y sub-superficie materiales tecnológicos.
Después de pasar revista a los fundamentos teóricos, se intentará resaltar la información
singular suministrada por esta técnica al analizar la composición química de la
superficie de algunos materiales metálicos de interés tecnológico.

The isolation of graphene by A. Geim and K. Novoselov made the material and its derivatives a matter of investigation for its properties and potential application. After an extended research of its properties, the greatest challenge that remains is to find a low cost and industrial scalable method to produce graphene and fabricate graphene based devices. One proposed method is the solution processing of graphene and its derivative graphene oxide.
Graphene oxide is an interesting material with various properties including sensitivity to various gases and high optical transmittance. The most fascinating property of graphene oxide is its ability to form graphene through reduction processes. Although various reduction methods have been proposed, most them demand high temperature (thermal or solvothermal reduction), may include hazardous materials (hydrazine reduction), or demand expensive equipment (UV-light reduction).
In this work, a low cost thermal reduction is proposed, and two different device configurations are examined. In the first device configuration, graphene oxide is deposited on top of glass substrate and the electrical behavior of the device was investigated, before and after reduction. For the planar device, the reduction process increased graphene oxide’s conductivity by over 4 orders of magnitude. Furthermore, the reduction of graphene oxide is restricted, in terms of reductions steps, depending on the thickness of the device.
The second device configuration is a Schottky junction of graphene oxide and crystalline silicon and the effect of thickness and quality of the GO film to the electrical properties of the junction before and after reduction is studied. In this case, the reduction strongly affects the contact resistance Rs of GO/Si. Furthermore, the contact resistance, the mean barrier height and the standard deviation of the GO/Si can be used to identify the quality of the GO film. Finally, a rectifying behavior is found between graphene oxide and aluminum that favors the electron over the hole conduction, which needs to be investigated.

The present thesis work concerns the synthesis and processing of nanostructured materials for supercapacitor applications. Various nanostructured materials were synthesized and subsequently processed into thin film electrodes at a laboratory and/or semi-industrial scale which were then investigated for their potential application as supercapacitor electrodes.

In the first part of the work, a spray deposition technique for the manufacture of 1,500 cm2 area electrodes with thickness from 10-25 nm to typically 1-2 micrometers was developed, optimized and validated. First films of multi-walled carbon nanotubes with demonstrated uniformity of thickness, microstructure, and electrochemical properties across the 1,500 cm2 area were manufactured.

Next, molybdenum trioxide was investigated for its potential application
as supercapacitor electrode. alpha-MoO3 nanobelts were synthesized using a hydrothermal method and spray deposited electrodes were tested in various electrolytes. Cyclic voltammetry of alpha-MoO3 nanobelt electrodes in aqueous electrolytes showed the greatest charge storage in 1 M H2SO4 with a complex redox activity in a 0 to 1 V (vs Ag/AgCl) electrochemical window. The oxido-reduction processes were then investigated by a combination of X-ray photoelectron spectroscopy and electrochemical characterization methods. The charge storage properties of alpha-MoO3/SWNTs (75 %/ 25 % w/w) (MOSC) electrodes were investigated in LiClO4/propylene carbonate in a 1.5 to 3.5 V vs Li/Li+ (half cell). Cyclic voltammetry was performed at scan rates from 0.1 mV/s to 50 mV/s and the separate contributions to charge storage of capacitive and diffusion-controlled 3D ion intercalation processes were estimated.

Graphene electrodes were manufactured by a surfactant-water based exfoliation method followed by spray-deposition. Cyclic voltammetry and galvanostatic charge-discharge experiments revealed a combination of electric double layer and pseudocapacitive behavior that was maintained to unusually high scan rates of 10,000  mV/s.

Finally, the high power density of graphene and high energy density of
single-walled carbon nanotubes were combined in a hybrid electrode manufactured following a layer by layer approach (LBL).

Nanotechnology, which deals with features as small as a 1 billionth of a meter, began to enter into mainstream physical sciences and engineering some 20 years ago. Recent applications of nanoscience include the use of nanoscale materials in electronics, catalysis, and biomedical research. Among these applications, strong interest has been shown to biological processes such as blood coagulation control and multimodal bioimaging, which has brought about a new and exciting research field called nanobiotechnology. Biotechnology, which itself also dates back ∼30 years, involves the manipulation of macroscopic biological systems such as cells and mice in order to understand why and how molecular level mechanisms affect specific biological functions, e.g., the role of APP (amyloid precursor protein) in Alzheimer’s disease (AD). This review aims (1) to introduce key concepts and materials from nanotechnology to a non-physical sciences community; (2) to introduce several state-of-the-art examples of current nanotechnology that were either constructed for use in biological systems or that can, in time, be utilized for biomedical research; (3) to provide recent excerpts in nanotoxicology and multifunctional nanoparticle systems (MFNPSs); and (4) to propose areas in neuroscience that may benefit from research at the interface of neurobiologically important systems and nanostructured materials.

A systematic approach is required in order to determine the frictional characteristics of a contacting pair in the presence of a tribofilm. Despite the clear benefits in functionality and in reducing wear, the generation of ZDDP-based tribofilms often lead to increased frictional losses. Such an increase is also observed in the tribometric tests reported here, as well as in open literature. This paper investigates the underlying mechanics for the rise in friction using an integrated methodology, based upon Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). The use of an analytical contact mechanics model demonstrates that the pressure coefficient of boundary shear strength, measured using lateral force microscopy, provides an explanation for the observed increase in measured friction at micro-scale.