Papers by Keyword: X-Ray Photoelectron Spectroscopy (XPS)

Abstract: Magnesium apatite (MA, (Ca₉Mg)(PO₄)₆(OH)₂) and Hydroxyapatite (HA) coatings were synthesized on Ti6Al4V substrates by a sol-gel dip coating method. Glucose and bovine serum albumin (BSA) were added to the standard simulated body fluid (SBF) separately to form organic-containing simulated body fluids. MA and HA coatings were immersed in standard and organic modified SBF for time periods of 4, 7, 14, 21 and 28 days at 37±1°C. The surface dissolution and deposition behavior of the coatings after soaking were examined with Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The results show that glucose in SBF has no apparent effect on the deposition of new apatite from the solution. BSA in SBF shows retardation effect on the deposition of apatite by forming a protein dominant globular layer. This layer inhibits the further deposition of apatite from SBF solution.

Abstract: A series of the magnesium apatite coatings according to (Ca_10-xMg_x)(PO₄)₆(OH)₂, where x = 0 to 2, was synthesized through a sol-gel dip-coating method. The roughness of the magnesium coatings increased as more magnesium incorporated into the coatings. The mechanical properties of the coatings were analyzed with Nanoindentor. The incorporation of magnesium decreased the hardness and the Young’s modulus of the coating. The X-ray Photoelectron Spectroscopy (XPS) analysis revealed that only part of magnesium was incorporated into the apatite structure while the rest existed in the form of MgO in the coating.

Abstract: Two silane-based hybrid coatings were developed to modify the surface energy of phenolic resin impregnated paper. The coated paper samples were further pressed onto surfaces of plywood. The surface properties and water repellence of coated paper were investigated by AFM, XPS and water contact angle measurements. The water absorption of plywood with pressed paper was studied by water uptake tests. It was found that the sol-gel coatings had slightly improved the water repellence of the impregnated paper. The water absorption of plywood was also slightly decreased.

Abstract: (La_0.7Sr_0.3)MnO3 (LSMO) thin films were grown on Si (100) substrate by using pulsed laser deposition (PLD) process. Both structure and surface morphology of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). Furthermore, the chemical states and chemical composition of the films were determined by X-ray photoelectron spectroscopy (XPS) near the surface. From XRD, the results indicate that the films grown on Si (100) substrates have a single pseudocubic perovskite phase structure with a high (100) orientation. The XPS results show that La, Sr and Mn exist mainly in the forms of perovskite structure and a SrO layer was found on outermost surface. The films resistivity emeasured under room temperature is 6.4´10^-4 W×cm.

Abstract: Under mild conditions, trihydridosilanes interact with a variety of clean, hydrogenated and fresh metal and metalloid surfaces, including titanium, silicon and gold. In contrast, monohydridosilanes appear to have minimal interaction. All classes of hydridosilanes have minimal interaction with anhydrous oxide surfaces. Preliminary results suggest that surface modification with trihydridosilanes may provide a route for generating self-assembled monolayers on metal substrates. The synthesis of new trihydridosilanes is described. Contact angle, FTIR and XPS data for modified surfaces are provided.

Abstract: Amorphous alloys, in general, exhibit superior mechanical and chemical properties as compared to their crystalline counterparts, which is attributed to their chemical homogeneity and to the absence of crystal-like structural defects. Nanocrystalline and fully crystallized forms of these alloys can be easily obtained by a suitable thermal annealing treatment. It is important to have the knowledge of corrosion/oxidation behavior of amorphous and nanocrystalline alloys for various possible applications. In contrast to many investigations on corrosion and oxidation behavior of amorphous alloys reported in the literature, only limited studies have been carried out on comparison of corrosion/oxidation behavior of amorphous and nanocrystalline states of the same alloy. With this motivation potentiodynamic polarization studies were carried out on amorphous and nanocrystalline states of the alloy Ti60Ni40 in several aqueous media at room temperature. The oxidation in air was also investigated in the temperature range 2800C-3800C using a thermogravimetric analyzer. It was found from these investigations that nanocrystalline state exhibits the maximum corrosion/oxidation resistance in comparison to amorphous and crystalline states. The better corrosion/oxidation resistance of nanocrystalline state can be explained in terms of the nature of the nanocrystalline phase/phases and the size of the crystallites. The results of the present study are supported by other similar studies reported in the literature. A short review on comparison of corrosion/oxidation behaviour of amorphous and nanocrystalline Ti-based alloy is also presented in the paper.

Abstract: ZnO doped with a few per cent of magnetic ions such as Ni, Fe, Co exhibits room temperature ferromagnetism (RTFM), transforming it into a very promising candidate for future spintronic applications. Two samples i.e. ZnO doped with Ni and Cr (5% each) have been investigated in the present work. The samples were characterized by Rietveld refinement of X-ray diffraction (XRD) patterns and the superconducting quantum interference device (SQUID) magnetometry. Rietveld analysis confirms that both the polycrystalline samples possess wurtzite structure with no evidence of any secondary phase. The SQUID measurements exhibit a diamagnetic state for the pristine ZnO and a paramagnetic state for the as-synthesized (Cr and Ni)-doped ZnO samples. However, the post annealing in H2 and vacuum drive them to a remarkable ferromagnetic state at room temperature. No element specific signature for ferromagnetism was seen. Then the X-ray photoelectron spectroscopic (XPS) measurements were performed to investigate their electronic structure and exploring the origin of ferromagnetism in these diluted magnetic semiconductor materials. The XPS results confirm the creation of oxygen vacancies upon Hydrogen/ vacuum annealing, owned to the (Ni/Cr) 3d¬−O 2p hybridization. The findings suggest oxygen vacancies as the intrinsic origin for ferromagnetism in doped ZnO. The important feature of this work is that the ferromagnetism and the consequent electronic property changes are found to be reversible with regard to re-heating the samples in air, showing a switch “on” and “off” ferromagnetic ordering in the ZnO matrix.

Abstract: There has been a rapidly increasing interest in the synthesis and characterization of Si- nanostructures embedded in a dielectric matrix, as it can lead to energy-efficient and cost-effective Complementary Metal-Oxide-Semiconductor (CMOS)-compatible Si-based light sources for optoelectronic integration. In the present contribution, first an overview of the SiOx as a dielectric matrix and its limitations are discussed. We then review the literature on hydrogenated amorphous silicon nitride (a-SiNx:H) as a dielectric matrix for Si-nanostructures, which have been carried out using silane (SiH4) and ammonia (NH3) as the reactant gases. Our studies demonstrate that the least amount of hydrogen in the as-deposited (ASD) a-SiNx:H films not only allows in-situ formation of Si-nanostructures but also stabilizes silicon nitride (Si3N4) phase. The recent advances made in controlling the shape and size of Si-nanostructures embedded in a-SiNx:H matrix by swift heavy ion (SHI) irradiation are briefly discussed.

Abstract: In this paper, two types of fiber surface treatment methods, namely heat treatment and chemical coupling, were used to improve the basalt fiber surface properties. The basalt fiber surface was heated under 250Celsius degree for 30minites, and then was treated by silane coupling agent ethanol solution with different concentrations. X-ray photoelectron spectroscopy (XPS) was utilized to study the surface chemical compositions of basalt fiber after treatments. The XPS analysis indicated that chemical bonds between basalt fiber and KH-550 have occurred, and silanols were adsorbed to the surface of basalt fibers by an ether linkage between the silanols and the hydroxyl groups of the fibers. When the concentration of KH-550 is 0.8wt%, the optimal bonding condition is formed between basalt fiber and silane coupling agent.

Abstract: To understand the role of annealing conditions on the segregation and selective oxidation phenomena, Fe 2Mn 2Si 0.8Cr (all in wt.%) model alloy was investigated. The samples were annealed at 820°C in N2-5%H2 forming gas atmospheres over a wide range of dew pints (-80 to 0°C) with dwelling time of 1 to 5 minutes. At all dew points, the strong chemical interaction between Mn and Si causes the formation of manganese silicates. External oxidation of Mn, Si and Cr were decreased at the higher dew points. Increasing the dwelling time shows an extended oxidation front i.e. pronounced external/internal oxidation of Mn, Si and Cr. Basically, the present work addresses the two stages of oxidation front.