C. Palacio

Towards nanometric resolution in multilayer depth profiling: a comparative study of RBS, SIMS, XPS and GDOES

An increasing amount of effort is currently being directed towards the development of new functionalized nanostructured materials (i.e., multilayers and nanocomposites). Using an appropriate combination of composition and microstructure, it is possible to optimize and tailor the final properties of the material to its final application. The analytical characterization of these new complex nanostructures requires high-resolution analytical techniques that are able to provide information about surface and depth composition at the nanometric level. In this work, we comparatively review the state of the art in four different depth-profiling characterization techniques: Rutherford backscattering spectroscopy (RBS), secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS) and glow discharge optical emission spectroscopy (GDOES). In addition, we predict future trends in these techniques regarding improvements in their depth resolutions. Subnanometric resolution can now be achieved in RBS using magnetic spectrometry systems. In SIMS, the use of rotating sample holders and oxygen flooding during analysis as well as the optimization of floating low-energy ion guns to lower the impact energy of the primary ions improves the depth resolution of the technique. Angle-resolved XPS provides a very powerful and nondestructive technique for obtaining depth profiling and chemical information within the range of a few monolayers. Finally, the application of mathematical tools (deconvolution algorithms and a depth-profiling model), pulsed sources and surface plasma cleaning procedures is expected to greatly improve GDOES depth resolution.

Ag+ release inhibition from ZrCN–Ag coatings by surface agglomeration mechanism : structural characterization

New multifunctional materials based on well-established materials to which functional properties are added, such as antibacterial performance, have become a relevant research topic, in order to meet the requirements of today’s technological advances. This paper reports the results of a detailed structural and chemical characterization study of ZrCN–Ag coatings produced by reactive magnetron sputtering, as well as the release of silver after immersion in a simulated body fluid (Hank’s balanced salt solution), which mimic the material behaviour within the human body. The chemical composition was evaluated by electron probe microanalysis, x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy, whereas the structure was assessed by Raman spectroscopy and x-ray diffraction. The material exhibits a homogeneous distribution of the elements throughout the films, with a (C + N)/Zr ratio of around 1.3 and 15 at% of silver. A mixture of amorphous (a-C and CNx) and crystalline phases (ZrCN) was identified. In addition, the silver was detected to be released in less than 0.7% of the total silver in the films, occurring during the first two hours of immersion; no further release was evidenced after this period of time. (Some figures may appear in colour only in the online journal)

Ag-Ti(C,N)-based coatings for biomedical applications : influence of silver content on the structural properties

Ag–TiCN coatings were deposited by dc reactive magnetron sputtering and their structural and morphological properties were evaluated. Compositional analysis showed the existence of Ag–TiCN coatings with different Ag/Ti atomic ratios (ranging from 0 to 1.49). The structural and morphological properties are well correlated with the evolution of Ag/Ti atomic ratio. For the samples with low Ag/Ti atomic ratio (below 0.20) the coatings crystallize in a B1-NaCl crystal structure typical of TiC0.3N0.7. The increase in Ag/Ti atomic ratio promoted the formation of Ag crystalline phases as well as amorphous CNx phases detected in both x-ray photoelectron spectroscopy and Raman spectroscopy analysis. Simultaneously to the formation of Ag crystalline phases and amorphous carbon-based phases, a decrease in TiC0.3N0.7 grain size was observed as well as the densification of coatings.

XPS and ARXPS study of silver underpotential deposition on platinum in acid solution

Abstract The underpotential deposition (upd) of silver on polycrystalline platinum electrodes has been studied using electrochemical techniques and X-ray photoelectron spectroscopy (XPS). Under the electrochemical experimental conditions used for deposition, the cathodic ( q c ) voltammetric charge density is around 200 μC m −2 which is equivalent to ∼1.2 ML of deposited silver. XPS and angle-resolved X-ray photoelectron spectroscopy (ARXPS) were used to determine the chemical composition of the deposited films. Two different approaches have been used to extract the concentration depth profiles from ARXPS measurements: (a) a simple parametric model with some hypotheses about the form of the depth profile and (b) a general algorithm that uses regularization and singular value decomposition (SVD) techniques. The structure and composition of the films is rather complex. The upd deposition of silver yields films with concentration gradients that can be modeled by a multilayer structure involving silver islands. Starting from the outer surface, the predominant species are C, O+S+Ag, and the platinum substrate.

Microsensors based on GaN semiconductors covalently functionalized with luminescent Ru(II) complexes.

Covalent tethering of a Ru(II) dye to gallium nitride surfaces has been accomplished as a key step in the development of innovative sensing devices in which the indicator support (semiconductor) plays the role of both support and excitation source. Luminescence emission decays and time-resolved emission spectra confirm the presence of the dye on the semiconductor surfaces, while X-ray photoelectron spectroscopy proves its covalent bonding. The O(2) sensitivity of the new device is comparable to those of other ruthenium-based sensor systems. This achievement paves the way to a new generation of integrable ultracompact microsensors that combine semiconductor emitter-probe assemblies.

Study of Ni–Al interface formation

Abstract Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and factor analysis (FA) have been used to characterize the interface formation during the deposition of nickel on aluminum substrates at room temperature. The analysis of the shape of AES and EELS lines suggests the formation of a Ni–Al compound during the first stages of the deposition. Application of FA to the low-energy Auger electron spectra gives three principal factors that can be attributed to metallic aluminum, metallic nickel and nickel aluminide, respectively. These results, in addition to those on the evolution of the Ni LVV versus the Al LVV Auger intensity, are consistent with the formation of three monolayers of a Ni x Al compound with an average composition of x ≈2, followed by a layer by layer growth of Ni on the Ni x Al interface.

Direct Grafting of Long-Lived Luminescent Indicator Dyes to GaN Light-Emitting Diodes for Chemical Microsensor Development

Two new methods for covalent functionalization of GaN based on plasma activation of its surface are presented. Both of them allow attachment of sulfonated luminescent ruthenium(II) indicator dyes to the p- and n-type semiconductor as well as to the surface of nonencapsulated chips of GaN light-emitting diodes (blue LEDs). X-ray photoelectron spectroscopy analysis of the functionalized semiconductor confirms the formation of covalent bonds between the GaN surface and the dye. Confocal fluorescence microscopy with single-photon-timing (SPT) detection has been used for characterization of the functionalized surfaces and LED chips. While the ruthenium complex attached to p-GaN under an oxygen-free atmosphere gives significantly long mean emission lifetimes for the indicator dye (ca. 2000 ns), the n-GaN-functionalized surfaces display surprisingly low values (600 ns), suggesting the occurrence of a quenching process. A photoinduced electron injection from the dye to the semiconductor conduction band, followed by a fast back electron transfer, is proposed to be responsible for the excited ruthenium dye deactivation. This process invalidates the use of the n-GaN/dye system for sensing applications. However, for p-GaN/dye materials, the luminescence decay accelerates in the presence of O(2). The moderate sensitivity is attributed to the fact that only a monolayer of indicator dye is anchored to the semiconductor surface but serves as a demonstrator device. Moreover, the luminescence decays of the functionalized LED chip measured with excitation of either an external (laser) source or the underlying LED emission (from p-GaN/InGaN quantum wells) yield the same mean luminescence lifetime. These results pave the way for using advanced LEDs to develop integrateable optochemical microsensors for gas analysis.

Silver activation on thin films of Ag–ZrCN coatings for antimicrobial activity

Nowadays, with the increase of elderly population and related health problems, knee and hip joint prosthesis are being widely used worldwide. However, failure of these invasive devices occurs in a high percentage thus demanding the revision of the chirurgical procedure. Within the reasons of failure, microbial infections, either hospital or subsequently-acquired, contribute in high number to the statistics. Staphylococcus epidermidis (S. epidermidis) has emerged as one of the major nosocomial pathogens associated with these infections. Silver has a historic performance in medicine due to its potent antimicrobial activity, with a broad-spectrum on the activity of different types of microorganisms. Consequently, the main goal of this work was to produce Ag-ZrCN coatings with antimicrobial activity, for the surface modification of hip prostheses. Thin films of ZrCN with several silver concentrations were deposited onto stainless steel 316 L, by DC reactive magnetron sputtering, using two targets, Zr and Zr with silver pellets (Zr+Ag target), in an atmosphere containing Ar, C2H2 and N2. The antimicrobial activity of the modified surfaces was tested against S. epidermidis and the influence of an activation step of silver was assessed by testing samples after immersion in a 5% (w/v) NaClO solution for 5 min. The activation procedure revealed to be essential for the antimicrobial activity, as observed by the presence of an inhibition halo on the surface with 11 at.% of Ag. The morphology analysis of the surface before and after the activation procedure revealed differences in silver distribution indicating segregation/diffusion of the metallic element to the films surface. Thus, the results indicate that the silver activation step is responsible for an antimicrobial effect of the coatings, due to silver oxidation and silver ion release.

Chromium silicide formation by argon irradiation of Cr/Si bilayers

Chromium/silicon interfaces produced by Cr thin film deposition on Si substrates were ion-beam mixed using Ar+ ions at 3?keV. The ion-beam mixing (IBM) has been studied by means of x-ray photoelectron spectroscopy and factor analysis (FA). FA of the Si 2p and Cr 2p core levels shows that the kinetics of interface formation by IBM is characterized by two stages. During the first stage, a strong decrease in metallic Cr species is observed up to ion doses of ~1.5 ? 1016?ions?cm?2, not only due to sputtering but also due to the formation of chromium silicide. The second stage is characterized by a similar evolution of the chromium silicide species related to Cr and Si, respectively, suggesting that the stoichiometry of the chromium silicide formed is nearly constant. Finally, with increasing sputtering time, the signals associated with the silicide slowly decrease, and pure Si0 species begin to appear, since no free metallic chromium atoms are available to react with the unlimited silicon supply from the substrate. The comparison of the experimental results with those obtained from TRIDYN simulations suggests that pure ballistic ion mixing mechanisms alone are unable to explain experimental results, and other radiation-enhanced diffusion mechanisms must be considered to explain the IBM of Cr/Si interfaces by low-energy Ar+ ions.

Influence of culture media on the physical and chemical properties of Ag-TiCN coatings

The aim of this study was to verify the possible physical and chemical changes that may occur on the surface of Ag?TiCN coatings after exposure to the culture media used in microbiological and cytotoxic assays, respectively tryptic soy broth (TSB) and Dulbeccos modified eagles medium (DMEM). After sample immersion for 24?h in the media, analyses were performed by glow discharge optical emission spectroscopy discharge radiation (GDOES), Rutherford backscattering spectroscopy (RBS) and x-ray photoelectron spectroscopy (XPS). The results of GDOES profile, RBS and XPS spectra, of samples immersed in TSB, demonstrated the formation of a thin layer of carbon, oxygen and nitrogen that could be due to the presence of proteins in TSB. After 24?h of immersion in DMEM, the results showed the formation of a thin layer of calcium phosphates on the surface, since the coatings displayed a highly oxidized surface in which calcium and phosphorus were detected. All these results suggested that the formation of a layer on the coating surface prevented the release of silver ions in concentrations that allow antibacterial activity.