Ion Beam Depth Profiling Research Articles

Time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy study of 2-phenylimidazole on brass.

This work presents the first surface analysis investigation of 2-phenylimidazole (PhI) as a corrosion inhibitor for brass in a 3 wt.% NaCl solution using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS). A time-of-flight secondary ion mass spectrometer was used to describe the elemental and molecular specific signals on the brass surface. Gas cluster/monoatomic ion beam depth profiling and two-dimensional (2D) imaging showed the surface properties of the PhI surface layer. In addition, detailed XPS was used to describe the element-specific signals on the brass surface. Furthermore, principal component analysis demonstrated the distribution of the different phases of the surface. Finally, the applicability of PhI in hot corrosion studies was suggested by a thermal stability experiment. TOF-SIMS measurements showed an intense positive-ion TOF-SIMS signal for protonated PhI, i.e. C9 H9 N2 + at m/z 145.07. Moreover, there was an intense negative-ion TOF-SIMS signal for deprotonated PhI, i.e. C9 H7 N2 ¯ at m/z 143.06. Gas cluster ion beam sputtering associated with the analysis of the XPS-excited Cu L3 M4,5 M4,5 revealed a connection between Cu(I) and PhI to form organometallic complexes. The formation of the organometallic complexes with Cu and Zn metal atoms/ions was identified using TOF-SIMS in positive and negative polarity mode: PhI-Cu, PhI-Cu2 , PhI-Zn, and PhI-Zn2 complexes were present on the brass surface. The TOF-SIMS measurements were supported by XPS measurements.

Vapor-phase Surface Cleaning of Electroplated Cu Films Using Anhydrous N2H4

Cleaning of copper surfaces is required to remove undesired surface oxidation during the interconnect fabrication process. In this work, we examined the vapor-phase cleaning of Cu surfaces using anhydrous N2H4. Gas cluster ion beam (GCIB) depth profiling and elemental analysis using XPS shows that CuxO in the Cu sample, formed after exposure to air, can be effectively reduced to Cu0 at 200 °C. By monitoring the surface chemistry using in-situ reflectance absorption infrared spectroscopy (RAIRS), we found that atomic layer deposition (ALD)-like single exposure of N2H4 at 200 °C can remove the adventitious surface contamination and, most importantly, reduce the Cu2O to metallic Cu.

Hybrid Perovskites Depth Profiling with Variable-Size Argon Clusters and Monatomic Ions Beams.

Ion beam depth profiling is increasingly used to investigate layers and interfaces in complex multilayered devices, including solar cells. This approach is particularly challenging on hybrid perovskite layers and perovskite solar cells because of the presence of organic/inorganic interfaces requiring the fine optimization of the sputtering beam conditions. The ion beam sputtering must ensure a viable sputtering rate on hard inorganic materials while limiting the chemical (fragmentation), compositional (preferential sputtering) or topographical (roughening and intermixing) modifications on soft organic layers. In this work, model (Csx(MA0.17FA0.83)100−xPb(I0.83Br0.17)3/cTiO2/Glass) samples and full mesoscopic perovskite solar cells are profiled using low-energy (500 and 1000 eV) monatomic beams (Ar+ and Cs+) and variable-size argon clusters (Arn+, 75 < n < 4000) with energy up to 20 keV. The ion beam conditions are optimized by systematically comparing the sputtering rates and the surface modifications associated with each sputtering beam. X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and in-situ scanning probe microscopy are combined to characterize the interfaces and evidence sputtering-related artifacts. Within monatomic beams, 500 eV Cs+ results in the most intense and stable ToF-SIMS molecular profiles, almost material-independent sputtering rates and sharp interfaces. Large argon clusters (n > 500) with insufficient energy (E < 10 keV) result in the preferential sputtering of organic molecules and are highly ineffective to sputter small metal clusters (Pb and Au), which tend to artificially accumulate during the depth profile. This is not the case for the optimized cluster ions having a few hundred argon atoms (300 < n < 500) and an energy-per-atom value of at least 20 eV. In these conditions, we obtain (i) the low fragmentation of organic molecules, (ii) convenient erosion rates on soft and hard layers (but still different), and (iii) constant molecular profiles in the perovskite layer, i.e., no accumulation of damages.

Embedding-Free Method for Preparation of Cross-Sections of Organic Materials for Micro Chemical Analysis Using Gas Cluster Ion Beam Sputtering.

We present a novel in situ mask method for the preparation of cross-sections of organic materials such as polymer multilayer films suitable for chemical imaging of buried interfaces. We demonstrate this method on a model buried interface system consisting of a piece of Scotch tape adhered to a PET substrate and a protective film used in consumer packaging. A high dose of gallium from a focused ion beam (FIB) was used to produce a damaged overlayer on the surface of the organic sample. The damaged layer has a significantly slower sputter rate compared to the native undamaged organic material. Therefore, during gas cluster ion beam (GCIB) depth profiling experiments the damaged layer functions as a mask, protecting the sample beneath and producing a cross-section at the edge of the mask. The FIB itself cannot be used directly to prepare the cross-section since the organic materials are easily damaged. A four step workflow is described including a final cleaning procedure to remove redeposited material from the cross-section. The workflow is completed in a few hours for samples up to 100 μm thickness. The method does not require sample embedding and is suited to automated analysis, which can be important benefits for industrial analysis where a variety of samples are analyzed routinely.

State-of-Charge Mapping with Spatially Resolved XPS in Patterned Thin Film Battery Electrodes

Nanostructures offer the opportunity to design-in higher power capability and cycling robustness, but their spatial distribution of active ion storage material can pose major challenges in transporting electrons to all regions of active material. For example, high aspect ratio nanowire or nanotube electrodes on a planar current collector may require electrons to diffuse 10’s – 100’s μm though highly resistive oxide material before meeting an incoming lithium ion. While adding a conformal or coaxial current collector can improve performance at high rates, the characterization of this improvement must typically be inferred though bulk electrochemical measurements.In this work, we develop a model system with which to directly measure the spatial distribution of state-of-charge (SOC) for a poorly conductive cathode material as a function of distance from a current collector and discharge rate using spatially resolved x-ray photoelectron spectroscopy (XPS). Our system includes a geometrically restricted electrode/current collector interface but a relatively unrestricted electrode/electrolyte interface. We fabricate electrodes with patterned planar current collectors using standard microfabrication techniques and deposit pinhole-free ultrathin films of the cathode material V2O5 using atomic layer deposition. These cathodes are then discharged in a liquid electrolyte under different rates and conditions, and the resulting SOC distribution is mapped using XPS with a lateral resolution as good as 15µm. Unlike microspot Raman or XRD, XPS provides a direct quantitative measurement of the SOC through the concentration of lithium ions and/or reduced vanadium ions (Figure 1). The latter is particularly appealing in that it is independent of surface contamination, providing an avenue towards SOC characterization even in the presence of a thin SEI layer. We also explore the depth dependence of the SOC using angle resolved XPS and ion beam depth profiling. Our measurements demonstrate that the electrode SOC decreases over a distance of order millimeters from the current collector at moderate rates, and that the shape and magnitude of the SOC gradient depends on the discharge rate. Finally, we compare our observations with simulations of the structure using COMSOL Multiphysics, and attempt to resolve discrepancies between the two. We believe this approach can provide design guidance for heterogeneous nanostructures applied to electrical energy storage. We anticipate this technique to be broadly applicable to other electrode materials and active ions.

A new approach for determining accurate chemical distributions using in‐situ GCIB cross‐section imaging

Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) has become widely used to characterize various kinds of materials, especially organic materials. It has recently become possible to investigate the molecular distributions underneath the surface using Ar‐GCIB (gas cluster ion beam) depth profiling. It is an important new capability for practical use of TOF‐SIMS because the subsurface and interface chemistry plays an important role in the performance of many products. However, it is difficult to obtain accurate chemical depth distributions using sputter depth profiling when the sample has a significant surface roughness and/or inhomogeneous structure. In order to resolve this problem, we proposed an approach to determine the accurate chemical distributions using GCIB cross‐section imaging method. In this study, this approach was demonstrated for practical organic samples, and accurate chemical depth distributions were determined. Copyright © 2014 John Wiley &amp; Sons, Ltd.

XPS for non-destructive depth profiling and 3D imaging of surface nanostructures

Depth profiling of nanostructures is of high importance both technologically and fundamentally. Therefore, many different methods have been developed for determination of the depth distribution of atoms, for example ion beam (e.g. O(2)(+) , Ar(+)) sputtering, low-damage C(60) cluster ion sputtering for depth profiling of organic materials, water droplet cluster ion beam depth profiling, ion-probing techniques (Rutherford backscattering spectroscopy (RBS), secondary-ion mass spectroscopy (SIMS) and glow-discharge optical emission spectroscopy (GDOES)), X-ray microanalysis using the electron probe variation technique combined with Monte Carlo calculations, angle-resolved XPS (ARXPS), and X-ray photoelectron spectroscopy (XPS) peak-shape analysis. Each of the depth profiling techniques has its own advantages and disadvantages. However, in many cases, non-destructive techniques are preferred; these include ARXPS and XPS peak-shape analysis. The former together with parallel factor analysis is suitable for giving an overall understanding of chemistry and morphology with depth. It works very well for flat surfaces but it fails for rough or nanostructured surfaces because of the shadowing effect. In the latter method shadowing effects can be avoided because only a single spectrum is used in the analysis and this may be taken at near normal emission angle. It is a rather robust means of determining atom depth distributions on the nanoscale both for large-area XPS analysis and for imaging. We critically discuss some of the techniques mentioned above and show that both ARXPS imaging and, particularly, XPS peak-shape analysis for 3D imaging of nanostructures are very promising techniques and open a gateway for visualizing nanostructures.

Molecular depth profiling of polymers with very low energy ions

The need for a molecular depth profiling technique to study organic layers has become a strong incentive in the SIMS community in the last few years, especially with the recent successes obtained with cluster ion beam depth profiling. In this work, we have investigated a thoroughly different approach by using very low energy (down to 200 eV) monoatomic or diatomic ions to sputter organic matter. Quite surprisingly, we were able to retain specific molecular information on various polymers even at very high fluence. Polymethylmethacrylate (PMMA) and polyethylene terephthalate (PET) films were depth-profiled with 200 eV Cs + and 500 eV O 2 + ions. With 200 eV Cs ions, the best profiles were obtained in the negative mode, due to a strong negative ionisation yield enhancement related to Cs retention in the polymer. A relatively high and stable signal from the most characteristic ions was measured all over the layer. With 500 eV O 2 +, real molecular depth-profiles were also obtained in both the positive and the negative modes. Once again, the main characteristic fragments of PET or PMMA remain detectable with stable yields all over the profile.

C 60 ion sputtering of layered organic materials

Two different organic materials, Irganox1010 and Irganox3114, were vacuum deposited as alternating layers. The layers of Irganox3114 were thin (∼2.5 nm) in comparison to the Irganox1010 (∼55 or ∼90 nm); we call these ‘organic delta layers’. Both materials are shown to have identical sputtering yields and the alternating layers may be used to determine some of the important metrological parameters for cluster ion beam depth profiling of organic materials. The sputtering yield for C 60 ions is shown to diminish with ion dose. Comparison with atomic force microscopy data from films of pure Irganox1010, demonstrates that the depth resolution is limited by the development of topography. Secondary ion intensities are a well-behaved function of sputtering yield and may be employed to obtain useful analytical information. Organic delta layers are shown to be valuable reference materials for comparing the capabilities of different cluster ion sources and experimental arrangements for the depth profiling of organic materials.

Quantitative Molecular Depth Profiling of Organic Delta-Layers by C60 Ion Sputtering and SIMS

Alternating layers of two different organic materials, Irganox1010 and Irganox3114, have been created using vapor deposition. The layers of Irganox3114 were very thin ( approximately 2.5 nm) in comparison to the layers of Irganox1010 ( approximately 55 or approximately 90 nm) to create an organic equivalent of the inorganic 'delta-layers' commonly employed as reference materials in dynamic secondary ion mass spectrometry. Both materials have identical sputtering yields, and we show that organic delta layers may be used to determine some of the important metrological parameters for cluster ion beam depth profiling. We demonstrate, using a C(60) ion source, that the sputtering yield, S, diminishes with ion dose and that the depth resolution also degrades. By comparison with atomic force microscopy data for films of pure Irganox1010, we show that the degradation in depth resolution is caused by the development of topography. Secondary ion intensities are a well-behaved function of sputtering yield and may be employed to obtain useful analytical information. Fragments characteristic of highly damaged material have intensity proportional to S, and those fragments with minimal molecular rearrangment exhibit intensities proportional to S(2). We demonstrate quantitative analysis of the amount of substance in buried layers of a few nanometer thickness with an accuracy of approximately 10%. Organic delta layers are valuable reference materials for comparing the capabilities of different cluster ion sources and experimental arrangements for the depth profiling of organic materials.

Interaction of Human Plasma Fibrinogen with Commercially Pure Titanium as Studied with Atomic Force Microscopy and X-ray Photoelectron Spectroscopy

The surface of a biomaterial interacts with the body fluid upon implantation in the human body. The biocompatibility of a material is strongly influenced by the adsorption of proteins onto the surface. Titanium is frequently used as a biomaterial for implants in orthopedics and cardiovascular devices. Understanding the biocompatibility is very important to improve implants. The surface chemistry of an implant material and its influence on the interaction with body fluid is crucial in that perspective. The main goal of this study was to investigate the conformation of human plasma fibrinogen (HPF) adsorbed on commercially pure titanium (CP Ti) on a molecular level by means of ex situ atomic force microscopy (AFM). With X-ray photoelectron spectroscopy combined with argon ion beam depth profiling, it was shown that the oxide layer present at the surface was mainly composed of TiO2, with a small percentage of Ti2O3. Ex situ AFM imaging showed the conformation of HPF on CP Ti. Single molecules and aggregates of fibrinogen were observed. The trinodular structure of single HPF molecules (two spherical D domains at the distal ends of the extended molecule and the central spherical E domain) adsorbed onto CP Ti was visualized. Aggregate formation through the connection of the D domains of the HPF molecules was observed on CP Ti. The alphaC domains of HPF were not visible on CP Ti. The ex situ AFM images indicated conformational changes of HPF upon adsorption onto CP Ti. The conformation of the adsorbed HPF molecules was different on mica and titanium. The difference in wettability between both substrates caused a larger spread of the protein on the CP Ti surface and thus resulted in a larger perturbation to the native structure of HPF as compared to mica.

Analysis of simulated hypervelocity impacts on a titanium fuel tank from the Salyut 7 space station

The aim of this project was to gain a better understanding of the microstructural effects of hypervelocity impacts (HVI) in titanium alloys. We investigated a titanium fuel tank recovered from the Russian Salyut 7 space station, which was launched on April 19, 1982 before being destroyed during an un-controlled re-entry in 1991, reportedly scattering debris over parts of South America. Several sections were cut out from the tank in order to undergo HVI simulations using a two-stage light gas gun. In addition, a Ti–6Al–4V alloy was studied for further comparison. The crater morphologies produced were successfully characterised using microscope-based white light interferometry (Zygo ® Corp, USA), while projectile remnants were identified via secondary ion mass spectrometry (SIMS). Microstructural alterations were investigated using focused ion beam (FIB) milling and depth profiling, as well as transmission electron microscopy (TEM). There was evidence of a very high density of dislocations in the vicinity of the crater. The extent of the deformation was localised in a region of about one to two radii of the impact craters. No notable differences were observed between the titanium alloys used during the hypervelocity impact tests.

Dispersion of Gold in Polycarbonate by Vapor-Induced Crystallization

It has been demonstrated that dispersion of noble metal nanoparticles in an organic matrix can be achieved by crystallization of amorphous low-molecular-weight nylon-11 in a process called relaxative autodispersion. In the present paper we report the dispersion of Au by acetone vapor-induced crystallization of amorphous polycarbonate films. Crystallization kinetics were examined with infrared spectroscopy. Au dispersion was detected with X-ray photoelectron spectroscopy in conjunction with ion-beam depth profiling and cross-sectional transmission electron microscopy. While vapor sorption in films of some micrometers thickness occurs within minutes at room temperature, crystallization and Au dispersion take place on a time scale of hours. Crystallization gives rise to a strong enhancement of surface roughness measured by atomic force microscopy. The present approach of metal dispersion is not restricted to low-molecular-weight polymers. A model for the dispersion process is proposed.

Depth profiling of multilayers at elevated temperatures and at changeable ion beam parameters

The kinetics of surface composition during ion beam depth profiling of multilayers is considered. The experimental results obtained by AES at elevated temperatures and at changeable ion energy and incident angle are modelled. In order to find qualitative differences in depth profile spectra produced by surface processes and bulk processes separately, the modelling is performed by two models. First one includes the surface roughness development without ion mixing in bulk and second one includes ion mixing without surface roughness development. The origin of peak asymmetry is analysed by both models. As the main conclusion is that both processes may give qualitatively very similar effects in depth profile spectra and the interpretation of experimental results can be done only after quantitative theoretical analysis.

Limits of Ion-Beam Depth-Profiling as Used in Diffusion Studies of Oxidation-Sensitive Materials

Limits of Ion-Beam Depth-Profiling as Used in Diffusion Studies of Oxidation-Sensitive Materials

Blister formation of tungsten due to ion bombardment

Blisters formed at tungsten surfaces due to deuterium ion bombardment have been studied systematically in the energy range 100 eV to 1 keV. The bombardment with 1 keV D + at room temperature (RT) shows that the blister size increases and the number decreases with the deuterium fluence from 1×10 19 to 1×10 21 D +/ cm 2 . No blisters are found at elevated temperatures between 600 and 800 °C. For bombardment with an energy as low as 100 eV, blisters are observed at the high fluence of 1×10 21 D +/ cm 2 . The blister size increases and the number decreases with the bombardment energy. Combined with scanning electron microscopy (SEM) ion beam depth profiling measurements have been used to investigate the effect of blister formation on the trapping behavior of deuterium in tungsten. Double implantations, where 4 keV He + and 100 eV D +, respectively, were injected in W prior to the bombardment of 1 keV D + show a pronounced increase of deuterium retention and blister disappearance. Possible mechanisms are proposed to describe the observed phenomena.

Comparative Analysis of the Nucleation and Growth of Copper on Different Low-k Polymers

ABSTRACTIn this work we present investigations of the nucleation and growth of evaporated copper on several low-k polymers. The evolving interfaces were characterized using transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results were compared between the PMDA/ODA polyimide, Teflon AF 1601 and Silk®. A diffusion coefficient for copper atoms in Silk® determined by low energy ion-beam depth profiling in conjunction with XPS is reported.

Isotope effect of diffusion in the supercooled liquid state of bulk metallic glasses

The isotope effect, E=(Dα/Dβ−1)/(mβ/mα−1), of cobalt diffusion in the deeply supercooled liquid state of the bulk metallic glass formers Zr46.7Ti8.3Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5 has been measured employing the radiotracers 57Co and 60Co in conjunction with serial sectioning by means of ion-beam depth profiling. In both alloys a small mass dependence with E≈0.10 is observed. This dependence has no temperature dependence in a range of 120 K in the supercooled liquid state encompassing four orders of magnitude in the diffusivity. We suggest that these results show that long-range diffusion in a deeply supercooled liquid is not mediated by viscous flow but proceeds by collective hopping processes involving about 10 atoms.

Auger depth profiles and stud pull adhesion of metal films on graphite–epoxy composites

Ion beam depth profiling and Auger electron spectroscopy (AES) have been used to characterize sputtered metal films on graphite epoxy composite substrates, with emphasis on elemental analysis of the interface between film and substrate. The AES data are correlated with adhesion strength values, obtained by the stud pull method. Films studied include chromium, nickel, titanium, tantalum, platinum, and vanadium, deposited by RF planar diode sputtering in thicknesses from 0.5 micrometers to 1.5 micrometers on substrates of graphite epoxy composite (Fiberite 934). The AES/ion beam etch profiling technique was used to determine the atomic concentration of oxygen, carbon, and the deposited metal, from the outer surface through the depth of the film, into the substrate. Atomic concentration profiles are presented for each metal and correlated with adhesion strengths, substrate preparation, and sputtering conditions. High adhesion strengths for Cr and Ti films are associated with elevated oxygen concentrations in the films, while the strong adherence of Ni to graphite–epoxy is associated with very low oxygen content. Lack of adhesion of Pt and Ta to graphite–epoxy is also associated with relatively low oxygen content in the metal/graphite–epoxy interface.

High temperature H and D behaviour in solid and liquid beryllium

We present the salient features and interpretations from a multi-technique study of the high temperature H isotope behaviour in Be, including liquid Be. The effects of the implantation of H or D ions in Be at 300 to 983 K as well as the effects of in situ annealing in the transmission electron microscope and annealing with a 30 ns laser pulse were investigated. Quantitative measurements of the gas release, ion-beam depth profiling, scanning electron and atomic force microscopy, and numerical modeling were used in the analysis. For H Be < 14% , the H trapping energy is 1.7 eV and diffusion out of the sample is effectively 10 times faster than anticipated from other work. The release is not connected with blister rupture. For H Be >- 14% , the trapping energy is only 1.0–1.2 eV, but explosive release can take place under some circumstances. The implications for Be plasma facing components in tokamaks are discussed.