Depth Distribution Of Elements Research Articles

In situ analysis of elemental depth distributions in thin films by combined evaluation of synchrotron x-ray fluorescence and diffraction

In this work we present a method for the in situ analysis of elemental depth distributions in thin films using a combined evaluation of synchrotron x-ray fluorescence and energy-dispersive x-ray diffraction signals. We recorded diffraction and fluorescence signals simultaneously during the reactive annealing of thin films. By means of the observed diffraction signals, the time evolution of phases in the thin films during the annealing processes can be determined. We utilized this phase information to parameterize the depth distributions of the elements in the films. The time-dependent fluorescence signals were then taken to determine the parameters representing the parameterized depth distributions. For this latter step, we numerically calculated the fluorescence intensities for a given set of depth distributions. These calculations handle polychromatic excitation and arbitrary functions of depth distributions and take into account primary and secondary fluorescence. Influences of lateral non-uniformities of the films, as well as the accuracy limits of the method, are investigated. We apply the introduced method to analyze the evolution of elemental depth distributions and to quantify the kinetic parameters during a synthesis process of CuInS2 thin films via the reactive annealing of Cu–In precursors in a sulfur atmosphere.

Editorial

Editorial

Diffusion and interface growth in hafnium oxide and silicate ultrathin films on Si(001)

Medium energy ion scattering has been used in combination with $^{16}\mathrm{O}$ and $^{18}\mathrm{O}$ isotope tracing to determine elemental depth distributions and elucidate oxygen transport in 2--5 nm thick HfO${}_{2}$ and HfSiO${}_{x}$ films grown by atomic layer deposition on Si(001). Both the oxygen isotope exchange rate in the dielectric as well as the interfacial silicon oxide growth rates were examined as a function of time, temperature, film stoichiometry (HfO${}_{2}$, HfSiO${}_{x}$, and HfSiO${}_{x}$N${}_{y}$), and crystallinity. The amount of exchanged oxygen in the oxide was found to decrease with increasing SiO${}_{2}$ content. When the SiO${}_{2}$ to HfO${}_{2}$ ratio reaches 1:1 in HfSiO${}_{x}$ an almost full suppression of the oxygen exchange is observed. The activation barrier for the SiO${}_{2}$ growth at the HfO${}_{2}$/Si and HfSiO${}_{x}$/Si interfaces was found to be much lower than that in the SiO${}_{2}$/Si and SiO${}_{x}$N${}_{y}$/Si cases, which is attributed to distinctly different oxygen incorporation mechanisms. The primary route for oxygen delivery to the interface responsible for the SiO${}_{2}$ growth is via exchange, however, direct oxidation by molecular oxygen cannot be discounted completely. In the presence of an interfacial nitride layer the $^{18}\mathrm{O}$-$^{16}\mathrm{O}$ exchange is replaced by the $^{18}\mathrm{O}$-N exchange, which slows diffusion and reduces the oxidation rate.

Ion Microscopy with Resonant Ionization Mass Spectrometry: Time-of-Flight Depth Profiling with Improved Isotopic Precision

There are four generally mutually exclusive requirements that plague many mass spectrometric measurements of trace constituents: (1) the small size (limited by the depth probed) of many interesting materials requires high useful yields to simply detect some trace elements, (2) the low concentrations of interesting elements require efficient discrimination from isobaric interferences, (3) it is often necessary to measure the depth distribution of elements with high surface and low bulk contributions, and (4) many applications require precise isotopic analysis. Resonant ionization mass spectrometry has made dramatic progress in addressing these difficulties over the past five years.

Effect of ECR-assisted microwave plasma nitriding treatment on the microstructure characteristics of FCVA deposited ultra-thin ta-C films for high-density magnetic storage applications

There are higher technical requirements for protecting layer of magnetic heads and disks used in future high-density storage fields. In this paper, ultra-thin (2 nm thickness) tetrahedral amorphous carbon (ta-C) films were firstly prepared by filtered cathodic vacuum arc (FCVA) method, then a series of nitriding treatments were performed with nitrogen plasma generated using electron cyclotron resonance (ECR) microwave source. Here it highlighted the influence of nitrogen flow and applied substrate bias voltage on the structural characteristics of ta-C films during the plasma nitriding process. The chemical compositions, element depth distribution profiles, physical structures and bonding configurations of plasma-nitrided ta-C films were investigated by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and UV–vis Raman spectroscopy. The experimental results show that the carbon nitride compounds (CN x ) are formed in nitrogenated ta-C films in which the N content and its depth distribution depends on bias voltage to large extent rather than N 2 flow. The N content of nitrogenated ta-C films can reach 16 at.% for a substrate bias of −300 V and a N 2 flow of 90 sccm. With increasing nitrogen content, there is less G peak dispersion and more ordering of structure. Furthermore, appropriate nitriding treatment (substrate bias: −100 V, N 2 flow: 150 sccm) can greatly increase the fraction of sp 3 and sp 3C–N bonds, but the values begin to fall when the N content is above 9.8 at.%. All these indicate that suitable ECR-assisted microwave plasma nitriding is a potential modification method to obtain ultra-thin ta-C films with higher sp 3 and sp 3C–N fractions for high-density magnetic storage applications.

X-ray fluorescence Kα/Kβ ratios for a layered specimen: Comparison of measurements and Monte Carlo calculations with the MCNPX code

This paper shows how the Monte Carlo N-Particle eXtended (MCNPX) computer code can easily be applied to calculate the Kα/Kβ ratios of elements distributed heterogeneously in an analyzed specimen. Experiments were performed on specimens made of thick substrates covered by one or two mono-elemental layers (Ti, Ni, and Cu) of intermediate thickness. The Kα/Kβ ratios of the elements present in a substrate and in the layers were measured and then compared with the ratios obtained with the MCNPX computer code and with simple analytical calculations. Good correspondence was achieved between the experimental and calculated values. It was demonstrated that the MCNPX code makes it possible to predict the Kα/Kβ ratios for a specimen composed of layers and a substrate. This code can be applied for recognizing sample homogeneity or the depth heterogeneity of a specimen. In addition, the depth distribution of elements can be estimated and then the coating thicknesses in layered samples can also be determined.

Analysis of the diffusion processes in Al/Cr, Al/Fe and Cr/Fe multilayers using the MRI model

One of the methods for synthesis of intermetallic films consists of two steps: deposition of a multilayer film containing monometallic layers, and consequential annealing to induce a diffusion process and alloy formation. Though the diffusion coefficients are generally known for couples of common metals, they can considerably differ for films deposited by PVD due to their specific microstructure. Bimetallic multilayers Al/Cr, Al/Fe and Cr/Fe were analysed as the first step for formation of the complex metallic alloy Al 4(Cr,Fe). The films were deposited by triode sputtering with a total thickness of about 250 nm and consisted of 6 layers. Annealing was performed in vacuum at temperatures 240–650 °C. The depth distributions of elements in the films annealed at various temperatures were measured by Auger electron spectroscopy. Detailed analysis of the profile was conducted using the MRI model, which takes into account interface broadening of the measured profile due to three reasons: ion-induced atom mixing, roughness, and information depth of analysed electrons. Thus we reconstructed the true depth profile of the as-deposited samples and profiles of the annealed samples that allowed us to extract the diffusion coefficients.

PIXE analysis of a painting by Giorgio Vasari

AbstractAmong ion beam analysis (IBA) techniques, particle induced x‐ray emission (PIXE) is the most widely used in the field of cultural heritage, providing the elemental composition of materials in a non‐invasive and non‐destructive way. This paper reports on the analysis by PIXE performed at one of the external beamlines of the 3 MV Tandetron accelerator of the LABEC laboratory (Istituto Nazionale di Fisica Nucleare (INFN)—Florence) on a wood painting by Giorgio Vasari, belonging to the altar‐piece ‘Pala Albergotti’ (church of Sts Flora and Lucilla, Arezzo). The measurements were taken in the framework of a campaign of scientific investigations, promoted by the Soprintendenza of Arezzo, preliminary to the restoration of the whole altar‐piece. PIXE was used to identify the elemental composition of the original materials and to characterise the alteration layer visible on the surface of the painting. Measurements on the same spot with proton beams of different energies (differential PIXE) also allowed us to get information on the depth distribution of elements and on the structure of layers without the need of picking up samples. Copyright © 2009 John Wiley & Sons, Ltd.

The action of molasses on properties of coatings obtained with electrodeposition from a SiO2 aqueous suspension

The effect of molasses added to a suspension on the properties of coatings obtained with electrodeposition is investigated. It is found that the combined action of molasses and an electric field makes it possible to obtain a homogeneous coating with the Si/O mass ratio constant in depth; there is no way to attain this constancy when employing an electric field only. In the absorption spectrum of coatings obtained in the presence of an electric field, a wide band is observed at 450 nm; in the process, the coating is kept transparent to the red spectral region radiation: this is responsible for its distinguishing brown coloring. The examination performed with different procedures allows one to infer that the presence of an electric field within the suspension induces the orientation of suspended particles, resulting in a greater packing density of particles forming the coating. The effect of molasses on the depth distribution of chemical elements in the coating is studied with glow discharge spectroscopy (GDS) and atomic force microscopy (AFM). In accordance with the investigations performed with these methods, the dominant chemical elements are evenly distributed in the coating obtained in the presence of an electric field. If molasses is present in the process of electrodeposition, the action of the field grows in orienting the particles, resulting in a more perfect coating structure and in upgrading of its quality.

Investigation of the structure of thinHfO2 films by soft x-ray reflectometry techniques

HfO2 thin films of different thicknesses and deposited by two methods (ALD and MOCVD) werestudied. The microstructure of films was characterized by reflection spectroscopy,x-ray diffraction (XRD), and soft x-ray reflectometry. It was established that theHfO2 film microstructure is closely dependent on film thickness. The 5 nm thick film synthesizedby ALD shows an amorphous phase while the film prepared by MOCVD wasinhomogeneous in depth and showed signs of crystalline structure. First results on thereconstruction of the depth distribution of chemical elements based on the analysis ofreflectivity curves are discussed.

Application of grazing incidence x-ray fluorescence technique to discriminate and quantify implanted solar wind

NASA launched the Genesis return mission to obtain pristine solar wind samples in order to better understand solar wind mechanics, solar physics, and solar system evolution. Unfortunately, the probe crash-landed shattering the collector plates necessitating the application of a grazing incidence x-ray fluorescence technique. This nondestructive methodology differentiates the terrestrial contamination from the low concentration implanted solar wind. Using this technique, the elemental depth distribution is obtained resulting in the determination of absolute solar wind elemental abundance. We describe this application and present the solar wind Fe concentration determination as an example.

Depth distributions of elements in monoatomic and compound coatings deposited onto copper and silicon by IBAD

One-component and multicomponent compound coatings were deposited on substrates of copper and silicon by the method of ion-beam assisted deposition. Atomic species sputtered from the inner surface of hollow truncated cones of different compositions were deposited on these substrates. AES and RBS were used to determine depth distributions of deposited elements. The depth of equal atomic concentrations of deposited and matrix has been considered as a depth marker of produced coatings. It was shown that the layer thickness does not depend on the substrate (copper and silicon in our study) and for a given coating composition is a linear function of the fluence. A few possible mechanisms of radiation-enhanced diffusion are discussed to explain observed phenomena.

Investigation of light element contents in subsurface layers of silicon

A special methodology for determination of light element concentrations in subsurface layers of solids is developed. The clue of this methodology is simultaneous application of Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection (ERD). The first analytical technique is used as a tool enabling the precise measurement of the number of He ions irradiating the target whilst the second one is appropriate for an analysis of a target containing light elements. The measurements of atomic concentrations in amorphous hydrogenated silicon carbide (a-SiC x :H) and in amorphous hydrogenated carbon (a-C:H) were done applying the described method (results for a-SiC x :H only are presented in the paper). The possibility for high precision measurements of depth distributions of light elements is also discussed.

Growth of graphite film over the tops of vertical carbon nanotubes using Ni/Ti/Si substrate

A substrate with Ni/Ti/Si structure was used to grow vertical carbon nanotubes (CNTs) with a graphite film over CNT tops by thermal chemical vapor deposition with CH 4 gas as carbon source. The carbon nanotubes and the substrate were characterized by a field emission scanning electron microscope for the morphologies, a transmission electron microscope for the microstructures, a Raman spectrograph for the crystallinity, and an Auger electron spectrometer for the depth distribution of elements. The result shows that when the thickness ratio of Ni layer to Ti layer in substrate is about 1, a graphite film with relatively good quality can be formed on the CNT tops.

ToF-SIMS study of official seals from Han Dynasty

Chinese bronze is a copper alloy containing copper, zinc, tin, lead, and other elements. ToF-SIMS has been used in the study of cultural heritage to establish authenticity, dating, origin, and the degradation process. In this study, static and dynamic SIMS was used to gain information regarding the surface composition and the depth distribution of important elements for a bronze lion and an official seal claimed as the Han Dynasty artifact (206 BC-220 AD). The results revealed that anticorrosion properties of surface layers exhibited were due to the higher percentage of nickel, but the major elements in the bulk of the artifact were copper and zinc. Surface enrichment of Au accords with the ancient Liujin method of developing a gold coating on metal object. These unique results demonstrated that ToF-SIMS is a potential tool to reveal processing methods for the ancient official seal.

Improvement on the Diffusion Barrier Performance of Reactively Sputtered Ru–N Film by Incorporation of Ta

Ultrathin Ru–N and Ru–Ta–N films ( in thickness) deposited by reactive sputtering are applied as a diffusion barrier in the Cu/barrier/ systems. After film deposition, the samples are tested before and after annealing at in vacuum for . The sheet resistance examined by four-point probe appraises that the Ru–Ta–N barrier would not fail until annealing at , as compared to Ru–N, which fails after annealing at . The depth distribution of elements examined by Auger electron spectroscopy confirms different degrees of Cu diffusion into underlayers for the two systems after annealing at . Also, the cross-sectional microstructures of the Cu/barrier/ samples analyzed by transmission electron microscopy, the crystallinity of barrier films examined by grazing incident angle X-ray diffraction, and the chemical state of barrier characterized by X-ray photoelectron spectroscope might explain the difference in barrier performance for the ultrathin Ru–N and Ru–Ta–N films in the Cu/barrier/ multilayered systems.

The change of atomic distribution and hardness by nitrogen implantation into aluminum alloy

Through many studies of the nitrogen implantation into aluminum alloy, researchers have concluded that AlN (aluminum nitride) formation is the key to hardening the aluminum surface. We implanted nitrogen ions into the Al6061, using an ion implanter which has a modified Bernas ion source. We changed the incident ion energies (25 keV, 50 keV) and fluences (1x10(17)-2x10(18) ions/cm(2)). To measure the depth hardness of implanted samples, we used nanoindentation test. The test results showed that the hardness of the implanted sample increased as the incident ion fluence increased until 1x10(18) ions/cm(2). However, the hardness did not increase at the fluence of 2x10(18) ions/cm(2). Furthermore, another result showed that the hardness was slightly decreased. To see the depth distribution of elements, we used Auger electron spectroscopy (AES) analysis with depth profiling. Through the AES analysis, we observed that the nitrogen atomic ratio did not increase; since the atomic ratio reached its maximum point (50%), the depth profile formed a flat curve in the AES. It is determined by the AlN structure (1:1 combination), that is, by the stoichiometrical rule. The nitrogen atoms diffused to the inner and outer sides rather than made a narrowly ranged accumulation. We observed that the flat curve was lowered downward a little at the fluence of 2x10(18) ions/cm(2). Observing the atomic distribution of oxygen in AES, we could conclude that the lowered curve was due to the recoil implantation of oxygen which had been originally combined with the aluminum surface in the aluminum oxide (Al(2)O(3)) layer. Comparing the AES result and the nanoindention result, we concluded that the recoiled oxygen atoms are not effective on hardening the Al surface. In this study, we observed the tendency to stop increasing the samples' hardness over the ion fluence of 1x10(18) ions/cm(2). We observed the saturation of the atomic ratio by the stoichiometrical rule.

Advanced ion energy loss models: Applications to subnanometric resolution elemental depth profiling

In principle, the depth distribution of the different chemical elements near the surface of solids can be determined quantitatively and absolutely with subnanometric depth resolution using medium energy ion scattering (MEIS), which is a refined version of Rutherford backscattering spectrometry (RBS). The energy resolution of current MEIS analyzers reveals spectral features that cannot be resolved using conventional RBS detectors. Thus, the usual data analysis framework based on a standard Gaussian approximation for the ion energy distribution in the target is applicable to regular RBS, but not generally to MEIS, in particular if one aims at subnanometric depth resolution. The observed asymmetry in the ion energy loss distributions is a direct consequence of the asymmetric character of inelastic energy transfers during individual atomic collisions and of the stochastic character of the resulting energy losses. We propose a model that accounts for the proper statistics of the small energy loss events and for an approximate electronic energy loss distribution during the backscattering event. The validity of this model is discussed and applied to the determination of HfO 2 and TiO 2 film thicknesses as well as to detect Al 2O 3 and HfO 2 intermixing. This final application case also illustrates the potentialities as well as some inherent limitations of MEIS. The model developed here has been made available to the public in the form of a software for MEIS data analysis.

Influence of aluminum ions implantation on corrosion behavior of zircaloy-2 alloy in 1 M H2SO4

The specimens were implanted with aluminum ions with fluence ranging from 1×1016 to 1×1017 ions/cm2 to study the effect of aluminum ion implantation on the aqueous corrosion behavior of zircaloy-2 by metal vapor vacuum arc source (MEVVA) at an extraction voltage of 40 kV. The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), respectively. Transmission electron microscopy (TEM) was used to examine the microstructure of the aluminum-implanted samples. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the aluminum ion implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted zircaloy-2 in a 1 M H2SO4 solution. It is found that a significant improvement was achieved in the aqueous corrosion resistance of zircaloy-2 implanted with aluminum ions. Finally, the mechanism of the corrosion behavior of aluminum-implanted zircaloy-2 was discussed.

Techniques for depth heterogeneity identification in X-ray fluorescence

Two methods enabling depth heterogeneity to be recognized and taken into account in quantitative analysis have been elaborated and then applied to various samples. The first method involves predicting the Kα/Kβ (or L lines) ratios for all identified elements. The second method is based on comparing the spectra measured on different geometric arrangements. In particular, sample tilting makes identification of depth heterogeneities possible. If the sample is heterogeneous, the heights of some peaks in the X-ray spectra change according to the depth distribution of the corresponding elements. Monte Carlo simulations with the MCNP4C2 code can be used to predict these changes and interpret the experimental results.