Sputter Depth Profiling Research Articles

Sputter-induced cross-contamination in analytical AES and XPS instrumentation: utilization of the effect for the in situ deposition of ultrathin functional layers

Cross-contamination is observed on sample surfaces by Auger electron spectroscopy and X-ray photoelectron spectroscopy if multiple samples are mounted on one sample holder and a neighbouring sample was sputter depth profiling. During sputter depth profiling, sputtered material is deposited on inner surfaces of the instrument. In a secondary sputter process, which is due to species leaving the primary sputter target with higher kinetic energy, the previously deposited material is transported from the inner surfaces to the other samples mounted on the sample holder. This reflective sputtering is utilized to deposit ultrathin layers on sample surfaces for X-ray photoelectron spectroscopy binding energy referencing purposes and to build up ultrathin conductive layers to make possible Auger electron spectroscopy measurements on insulating samples.

X-ray enhanced sputter rates in argon cluster ion sputter-depth profiling of polymers

The authors have observed for the first time that x-ray exposure of certain polymers of “degrading” type can greatly enhance the sputter rate of these polymers by gas cluster ion beam (GCIB) profiling. They have observed craters of similar dimensions to the x-ray spot well within the perimeter of sputter craters, indicating that x-rays can assist GCIB sputtering very significantly. This can be a major source of the loss of depth-resolution in sputter depth profiles of polymers. The authors have measured experimentally sputter craters in 14 different polymers by white-light interferometry. The results show that x-ray exposure can introduce much more topography than might previously have been expected, through both thermal and direct x-ray degradation and cross-linking. Within the region exposed to x-rays, the response of the polymer surface depends on its chemistry, with degrading (also known as type II) polymers being susceptible to large increases in sputter rate in some cases. For example, this leads to a sputter rate increase of a factor of 3 in poly-L-lactic acid (PLLA) compared to cluster-ion sputtering in the absence of x rays under typical experimental conditions. By comparison, crosslinking (also known as type I) polymers show either the same sputter rate or a reduced sputter rate due to crosslinking. The authors model this behavior using the bond scission parameter (GS) and crosslinking parameter (GX) used to model radiation damage in polymers. Agreement is good, allowing us to provide guidelines to assist in planning XPS depth-profiling experiments, in particular, for polymers such as PMMA and PLLA, where any requirement for uniform sputter rate is a more stringent limit to x-ray exposure than the requirement for the XPS spectra to represent chemical states quantitatively without damage.

Material dependence of argon cluster ion sputter yield in polymers: Method and measurements of relative sputter yields for 19 polymers

There is a pressing need for reference data to allow sputter depth-profiling of polymers using cluster and polyatomic ion sources for the quantification of depth in XPS and SIMS. The authors have developed a new method of sputter rate measurement based on a combination of contact masking and white-light interferometry. This allowed us to measure sputter rates for 19 different polymers of technological significance, a much wider set of data than any available previously. The results show a much larger range of sputter yield than might previously have been expected. For example, the sputter yield of PMMA being more than ten times that of poly ether ether ketone when using argon ion clusters of around 4 eV/atom, with other polymers being widely distributed between these extremes. Without reference data for sputter rate this wide range could lead to major errors in depth estimation in sputter depth-profiling of polymer coatings, biomaterials, nanostructures, polymer electronic and polymer photovoltaic devices.

Fabrication and characterization of iron and fluorine co-doped BST thin films for microwave applications

The effects of fluorine co-doping by means of a post-thermal annealing process of iron-doped BST thin films in a fluorine-containing atmosphere have been investigated. XPS and ToF-SIMS sputter depth profiling verified a homogeneous fluorine distribution in the thin films. By employing EPR, it was shown that singly charged ( $$ {\text{Fe}}_{\text{Ti}}^{\prime } $$ – $$ {\text{V}}_{\text{O}}^{ \cdot \cdot } $$ )· defect complexes, as well as ‘isolated’ $$ {\text{Fe}}_{\text{Ti}}^{\prime } $$ centres with a distribution of $$ {\text{F}}_{\text{O}}^{ \cdot } $$ sites in remote coordination spheres exist in the fluorinated films. Tunability enhancement due to fluorine co-doping as well as a Q-factor enhancement due to iron doping is demonstrated.

Characterization of Arsenic Contamination on Rust from Ton Containers

The speciation and spatial distribution of arsenic on rusted steel surfaces affect both measurement and removal approaches. The chemistry of arsenic residing in the rust of ton containers that held the chemical warfare agents bis(2-chloroethyl)sulfide (sulfur mustard) and 2-chlorovinyldichloroarsine (Lewisite) is of particular interest, because while the agents have been decontaminated, residual arsenic could pose a health or environmental risk. The chemistry and distribution of arsenic in rust samples were probed using imaging secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX). Arsenic in the III and or V oxidation state is homogeneously distributed at the very topmost layer of the rust samples and is intimately associated with iron. Sputter depth profiling followed by SIMS and XPS shows As at a depth of several nanometers, in some cases in a reduced form. The SEM/EDX ...

Embedded Palladium Activation as a Facile Method for TiO2‐Nanotube Nanoparticle Decoration: Cu2O‐Induced Visible‐Light Photoactivity

Embedded Palladium Activation as a Facile Method for TiO₂‐Nanotube Nanoparticle Decoration: Cu₂O‐Induced Visible‐Light Photoactivity

Effects of post oxidation annealing on electrical and interface properties of high pressure water vapor oxidized SiO2/SiC metal-oxide-semiconductor capacitors

Oxide has been grown on 4H-SiC samples using a high pressure oxidation system at temperature as low as 400 and 450°C using water vapor. Effect of post oxidation annealing (POA) in various ambient on electrical and structural properties of this oxide has been systematically investigated. X-ray photoelectron spectroscopy with sputter depth profile has been carried out to study the incorporation of nitrogen in the oxide. Significant nitrogen incorporation has been observed at the SiO2/SiC interface with POA in O2+N2 ambient resulting in effective passivation of the SiO2/SiC interface. This is reflected in the low interface state density and leakage current as well as high breakdown field strength for the samples with POA in O2+N2 compared to those for the sample with POA in N2. A very small hysteresis window (<10mV) also indicates low charge trapping and a good SiO2/SiC interface for the samples with POA in O2+N2.

Measuring the roughness of buried interfaces by sputter depth profiling

We report results of high-resolution sputter depth profiling of an alternating MgO/ZnO nanolayer stack grown by atomic layer deposition (ALD) of ≈5.5 nm per layer. We used an improved dual beam time-of-flight secondary ion mass spectrometer to measure 24Mg+ and 64Zn+ intensities as a function of sample depth. Analysis of depth profiles by the mixing–roughness–information model yields a 1.5 nm nanolayer interfacial roughness within the MgO/ZnO multilayer. This finding was cross-validated using specular x-ray reflectivity. Such an analysis further suggested that the 1.5 nm roughness corresponds to native/jig-sawed interfacial roughness rather than interfacial interdiffusion during the ALD growth.

Observations on X‐ray enhanced sputter rates in argon cluster ion sputter depth profiling of polymers

Traditionally polymer depth profiling by X‐ray photoelectron spectroscopy (XPS) has been dominated by the damage introduced by the ion beam rather than the X‐rays. With the introduction of polyatomic and especially argon gas cluster ion‐beam (GCIB) sources for XPS instruments, this is no longer the case, and either source of damage may be important (or dominate) under particular conditions. Importantly, while ion‐beam damage is a near‐surface effect, X‐ray damage may extend micrometres into the bulk of the sample, so that the accumulation of X‐ray damage during long depth profiles may be very significant. We have observed craters of similar dimensions to the X‐ray spot well within the perimeter of sputter craters, indicating that X‐rays can assist GCIB sputtering very significantly. We have measured experimentally sputter craters in 13 different polymers. The results show that X‐ray exposure can introduce much more topography than might previously have been expected, through both thermal and direct X‐ray degradation. This can increase the depth of a crater by a remarkable factor, up to three in the case of poly‐L‐lactic acid and polychlorotrifluorothylene under reasonably normal XPS conditions. This may be a major source of the loss of depth resolution in sputter depth profiles of polymers. Copyright © 2012 John Wiley &amp; Sons, Ltd.

An XPS study of bromine in methanol etching and hydrogen peroxide passivation treatments for cadmium zinc telluride radiation detectors

The performance of single crystal CdZnTe radiation detectors is dependent on both the bulk and the surface properties of the material. After single crystal fabrication and mechanical polishing, modification of the surface to remove damage and reduce the surface leakage current is generally achieved through chemical etching followed by a passivation treatment. In this work, CdZnTe single crystals have been chemically etched using a bromine in methanol (BM) treatment. The BM concentrations employed were 0.2 and 2.0 (v/v) % and exposure times varied between 5 and 120s. Angle resolved XPS and sputter depth profiling has been employed to characterize the surfaces for the different exposure conditions. A Te rich surface layer was formed for all exposures and the layer thickness was found to be independent of exposure time. The enriched Te layer thickness was accurately determined by calibrating the sputter rate against a CdTe layer of known thickness. For BM concentrations of 0.2 (v/v) % and 2 (v/v) %, the Te layer thickness was determined to be 1.3±0.2 and 1.8±0.2nm, respectively. The BM etched surfaces have subsequently been passivated in a 30wt.% H2O2 solution employing exposure time of 15s. The oxide layer thickness has been calculated using two standard XPS methodologies, based on the Beer–Lambert expression. The TeO2 thickness calculated from ARXPS data are slightly higher than the thickness obtained by the simplified Beer–Lambert expression. For BM exposures of 30–120s followed by a passivation treatment of 30wt. % H2O2 solution employing an exposure time 15s, the ARXPS method gave an average TeO2 thickness value of 1.20nm and the simplified Beer–Lambert expression gave an average thickness value of 0.99nm.

Effect of Cosputtering and Sample Rotation on Improving C60+ Depth Profiling of Materials

In the past decade, buckminsterfullerene (C(60))-based ion beams have been utilized in surface analysis instruments to expand their application to profiling organic materials. Although it had excellent performance for many organic and biological materials, its drawbacks, including carbon deposition, carbon penetration, continuous decay of the sputtering rate, and a rough sputtered surface, hindered its application. Cosputtering with C(60)(+) and auxiliary Ar(+) simultaneously and sample rotation during sputtering were proposed as methods to reduce the above-mentioned phenomena. However, the improvement from these methods has not been compared or studied under identical conditions; thus, the pros and cons of these methods are not yet known experimentally. In this work, a series of specimens including bulk materials and thin films were used to explore the differences between cosputtering and sample rotation on the analytical results. The results show that both of these methods can alleviate the problems associated with C(60)(+) sputtering, but each method showed better improvement in different situations. The cosputtering technique better suppressed carbon deposition, and could be used to generally improve results, especially with continuous spectra acquisition during sputtering (e.g., dynamic secondary ion mass spectrometry (SIMS) depth profiling). In contrast, for the scheme of sputter-then-acquire (e.g., alternative X-ray photoelectron spectrometry or dual-beam static SIMS depth profiling), a better result was achieved by sample rotation because it resulted in a flatter sputtered surface. Therefore, depending on the analytical scheme, a different method should be used to optimize the experimental conditions.

Energy and angle dependent photoemission study on Si/Ge multilayers using synchrotron radiation

The present report adds to the ongoing research on Si/Ge nanostructures by discussing the results obtained utilizing unique features of Synchrotron radiation (SR). Based on the structural and electronic properties of this system investigated in our earlier work, we have synthesized [Si(5 nm)/Ge(5 nm)]×10 multilayers (MLS) and exposed it to a range of incident photon energies (utilizing synchrotron radiation) and at different incident angles for the photoemission spectroscopic measurements. It is shown how the interface features are enhanced simultaneously suppressing the signals from topmost atomic layers. Also the effect of incident angle variation is discussed, which gives a clear picture of interface electronic properties of Si/Ge system. Significant changes in Si 3p, Ge 4p and s band features are observed in the valence band density of states. The overall results present an interesting observation of thoroughly investigating the basic building bilayer stack of the multilayer structure by combining energy and/or angle variation with low energy sputter depth profiling.

Evaluation of depth distribution and characterization of nanoscale Ta/Si multilayer thin film structures

A multilayer thin film structure of ten alternate Ta and Si layers with approximately 18nm thickness for the combined (Ta+Si) layer, was evaluated to explore the individual layer thickness and the interface mixing behavior using different surface characterization techniques like Time-of-Flight Secondary Ion Mass Spectrometry (TOFSIMS), X-ray Reflectometry (XRR) and Kelvin Probe Force Microscopy (KPFM). These results were compared with measurements performed earlier using cross section Transmission Electron Microscopy (TEM). The TOFSIMS depth profile results indicate the individual thickness of Si and Ta layers to be 8.1nm and 5.9nm respectively which are less than the corresponding actual thickness measured by cross section TEM as 10.5nm and 7.5nm. The difference in thickness measurement has been explained in the light of ion bombardment induced atomic mixing in the interface during sputter depth profiling. A scanning electron micrograph shows the actual crater and its edges created due to the sputtering including the multilayer for real view of the structure. The XRR observations however reveal better agreement with the cross section TEM data, both being non-destructive in nature. Attempts were made to characterize the multilayer using KPFM technique which clearly elucidated the grating type cross section of the structure.

Lithium orthosilicate surfaces: Characterization and effect on tritium release

Within the European Union, slightly hyperstoichiometric lithium orthosilicate has evolved as one of the candidate solid breeder materials for the helium cooled pebble bed blanket, which will be tested in ITER. In the past, several long-term irradiation experiments proved that lithium orthosilicate shows excellent tritium release behavior when purged with helium with 0.1% hydrogen.In this work, short-term irradiation experiments at the High Flux Reactor in Petten with two standard pebble qualities, as-received and heat-treated lithium orthosilicate were carried out to investigate possible differences in tritium release. Since the surface of the pebbles may play a significant role, especially for short-term irradiation, and the mechanism of desorption from the surface determines the chemical form and very likely the release rate of tritium, the aim of this work is to link the chemical composition of the surface to the Thermal Programmed Desorption (TPD) tritium release experiments. Therefore X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry were applied to characterize the surface of the unirradiated pebbles and to obtain sputter depth profiles of up to 800nm. In addition, X-ray diffractometry was used to determine the composition of phases of the samples before and after irradiation.

A statistical interpretation of molecular delta layer depth profiles

The delta layer depth response predicted by a simple statistical sputtering model is compared with molecular sputter depth profile data obtained on Langmuir–Blodgett delta layer systems. All input parameters of the statistical sputtering model are determined from low‐fluence molecular dynamics simulations performed for 20‐keV C60 cluster bombardment of silicon, making the model de facto parameter free. It is found that both calculated and measured depth response functions can be parametrised by the semiempirical Dowsett expression. The resulting parameters (leading and trailing edge slope, full‐width at half‐maximum) agree surprisingly well with those determined from the measured depth profiles. Copyright © 2012 John Wiley &amp; Sons, Ltd.

A statistical approach to delta layer depth profiling

We present a simple statistical model describing the removal and relocation of material during a sputter depth profiling experiment. All input parameters are determined from low‐fluence molecular dynamics simulations, making the model de facto parameter free. The model can be used to extrapolate data from the molecular dynamics simulations to projectile fluences relevant to sputter depth profiling experiments. As a result, the erosion of the surface is calculated in terms of fluence‐dependent filling factors of different sample layers. Using input data determined for the 20‐keV C60 cluster bombardment of silicon, it is found that a steady‐state erosion profile is reached after removal of approximately 20 monolayer equivalents of material. Plotting the contribution of particles from a specific layer to the instantaneous sputtered flux, one can directly determine the delta layer response function predicted from such a model. It is shown that this function can be parameterized by the semiempirical Dowsett response function, and the resulting fitting parameters are compared with published depth profile data. The model is then used to study the role of different processes influencing the observed depth resolution. We find that the statistical nature of the sputtering process suffices to explain many features of experimentally measured delta layer depth profiles. Copyright © 2012 John Wiley &amp; Sons, Ltd.

White light interferometry for quantitative surface characterization in ion sputtering experiments

White light interferometry (WLI) can be used to obtain surface morphology information on dimensional scale of millimeters with lateral resolution as good as ∼1μm and depth resolution down to 1nm. By performing true three-dimensional imaging of sample surfaces, the WLI technique enables accurate quantitative characterization of the geometry of surface features and compares favorably to scanning electron and atomic force microscopies by avoiding some of their drawbacks.In this paper, results of using the WLI imaging technique to characterize the products of ion sputtering experiments are reported. With a few figures, several example applications of the WLI method are illustrated when used for (i) sputtering yield measurements and time-to-depth conversion, (ii) optimizing ion beam current density profiles, the shapes of sputtered craters, and multiple ion beam superposition and (iii) quantitative characterization of surfaces processed with ions.In particular, for sputter depth profiling experiments of 25Mg, 44Ca and 53Cr ion implants in Si (implantation energy of 1keV per nucleon), the depth calibration of the measured depth profile curves determined by the WLI method appeared to be self-consistent with TRIM simulations for such projectile-matrix systems. In addition, high depth resolution of the WLI method is demonstrated for a case of a Genesis solar wind Si collector surface processed by gas cluster ion beam: a 12.5nm layer was removed from the processed surface, while the transition length between the processed and untreated areas was 150μm.

Alloying and surface composition of model Pd–Ag films synthesized by electroless deposition

PdAg model films and real composite membranes were prepared by sequential electroless deposition on top of porous stainless steel supports. Their surface properties were investigated by X-ray photoelectron spectroscopy (XPS), Angle resolved XPS and sputtering depth profile. It was shown that the surface of the alloy was strongly enriched in silver after the annealing treatment up to 500 °C on hydrogen stream. A relationship between the Ag 3d5/2 core-level binding energy shift and the silver surface composition was observed from the XPS data obtained with the model samples. The surface composition of real membranes after both hydrogen permeation and reaction experiments showed silver enrichment, in agreement with the data obtained from the model sample.

Influence of nonstationary atomic mixing on depth resolution in sputter depth profiling

Atomic mixing is an important parameter in the quantitative description of sputter depth profiles by the mixing‐roughness‐information depth model. By changing the atomic mixing length from zero to a stationary state value, it is possible to simulate the transient zone at the beginning of sputter depth profiling with noble gas ions, which is important for shallow depth profiles. Accordingly, the depth profile is gradually broadened and the depth resolution value increases with sputtered depth. Applications of changing the atomic mixing length in the mixing‐roughness‐information depth model are shown to yield excellent fits for measured AES depth profiles of N+ implantation in Co films. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Determination of Interdiffusion Coefficient in Nanolayered Structures by Auger Electron Spectroscopical Sputter Depth Profiling

A general method was developed for determination of interdiffusion coefficient in nanolayered structures by Auger electron spectroscopical (AES) sputter depth profiling. The procedures of this method are as follows: (1) the concentration depth profile of annealed sample is calculated from its as-grown layered structure by adopting a suitable diffusion model; (2) this diffusion concentration depth profile is convoluted with a resolution function provided by the mixing-roughness-information depth (MRI)-model and as a result a calculated AES depth profile is obtained; (3) the interdiffusion coefficient is determined by fitting the calculated AES depth profile to the measured one. As an example, the interdiffusion coefficient parameters, the pre-exponential factor and the activation energy, were determined as 4.7×10-18 m2/s and 0.76 eV, respectively, for a GexSi1-x/Si multilayered nanostructure with Ge-Si alloyed layers of 2.2, 4.3 and 2.2 nm thickness in Si matrix.