Secondary Ion Mass Spectrometry Signals Research Articles

Effectiveness of Wavelet Denoising on Secondary Ion Mass Spectrometry Signals

Wavelet theory has already achieved huge success. For Secondary Ions Mass Spectrometry (SIMS) signals, denoising the secondary signal, which is altered by the measurement, is considered that an essential step prior to applying such a signal processing technique that aims enhance the SIMS signals.The most efficient and widely used wavelet denoising method is based on wavelet coefficient thresholding. This process involves three important steps; wavelet decomposition: the input signals are decomposed into wavelet coefficients, thresholding: the wavelet coefficients are modified according to a threshold, and reconstruction: the modified coefficients are used in an inverse transform to obtain the noise-free-signal. Several researchers have used thresholding wavelet denoising techniques.
 The choice of wavelet type and the level of resolution can have a significant influence; it is important to note that the choice of resolution level depends on the type of signal we are dealing with, the nature of the present noise, and our specific goals for the denoised signal. It is generally recommended to test different resolution levels and evaluate their impact on the quality of the denoised signal before making a final decision. Moreover, the results obtained in wavelet denoising can be significantly influenced by the selection of wavelet types. The chosen wavelet type plays a crucial role in the extraction of signal details. Indeed, the effectiveness of denoising the MD6 sample has been demonstrated by the results obtained with sym4, db8, Haar and coif5 wavelets? These wavelets have effectively reduced noise while preserving crucial signal information, leading to an enhancement in the quality of the denoised signal.

Secondary ion mass spectrometry characterization of matrix composition in topological crystalline insulator [formula omitted

This study explores the use of Secondary Ion Mass Spectrometry (SIMS) to accurately measure the content of Pb1−xSnxTe, a new class of electronic materials known as Topological Crystalline Insulators (TCIs). We analyzed the SIMS signal ratios of SnCs+/PbCs+ and Sn±/Pb± in thin layers and determined the calibration curves necessary to estimate the exact amount of content in this ternary compound. Additionally, we investigated the matrix effect and performed depth profiling to obtain a more precise determination of the content. These findings contribute to the understanding and development of TCIs, and highlight the potential of SIMS for accurate content determination in ternary compounds.

Molecular Examination of Ion-Pair Competition in Alkaline Aluminate Solutions Using In Situ Liquid SIMS.

Understanding the structure and composition of aluminate complexes in extremely alkaline systems such as Bayer liquors has received enormous attention due to their fundamental and industrial importance. However, obtaining direct molecular information of the underlying ion-ion interactions using traditional approaches such as NMR spectroscopy or Raman spectroscopy is challenging due to the weakness of these interactions and/or their complex overlapping spectral signatures. Here, we exploit in situ liquid secondary-ion mass spectrometry (SIMS) as a new approach and show how it enables new insights. In contrast with traditional techniques, using SIMS we succeeded in acquiring information on dominant ion clusters in these alkaline systems. In Na+/K+ mixed alkaline aluminate solutions, we clearly observe preferential formation of Na+-anion clusters over K+-anion clusters. Evaluation of these clusters by density functional theory (DFT) calculations shows that these structures are stable and that their relative bond energies are consistent with their observed SIMS signal intensity differences. This demonstrates a key advantage of in situ liquid SIMS for overcoming ambiguities obscuring important information in these systems on constituent molecular clusters defined by relatively weak ion-pair competition and ion-solvent interactions.

Double perovskite cathodes for proton-conducting ceramic fuel cells: are they triple mixed ionic electronic conductors?

18O and 2H diffusion has been investigated at a temperature of 300 °C in the double perovskite material PrBaCo2O5+δ (PBCO) in flowing air containing 200 mbar of 2H216O. Secondary ion mass spectrometry (SIMS) depth profiling of exchanged ceramics has shown PBCO still retains significant oxygen diffusivity (~1.3 × 10−11 cm2s−1) at this temperature and that the presence of water (2H216O), gives rise to an enhancement of the surface exchange rate over that in pure oxygen by a factor of ~3. The 2H distribution, as inferred from the 2H216O− SIMS signal, shows an apparent depth profile which could be interpreted as 2H diffusion. However, examination of the 3-D distribution of the signal shows it to be nonhomogeneous and probably related to the presence of hydrated layers in the interior walls of pores and is not due to proton diffusion. This suggests that PBCO acts mainly as an oxygen ion mixed conductor when used in PCFC devices, although the presence of a small amount of protonic conductivity cannot be discounted in these materials.

Contamination-free Ge-based graphene as revealed by graphene enhanced secondary ion mass spectrometry (GESIMS)

In this study, we demonstrate that graphene grown on Ge does not contain any copper contamination, and identify some of the errors affecting the accuracy of commonly used measurement methods. Indeed, one of these, the secondary ion mass spectrometry (SIMS) technique, reveals copper contamination in Ge-based graphene but does not take into account the effect of the presence of the graphene layer. We have shown that this layer increases negative ionization significantly, and thus yields false results, but also that the graphene enhances, by an order of two, the magnitude of the intensity of SIMS signals when compared with a similar graphene-free sample, enabling much better detection limits. This forms the basis of a new measurement procedure, graphene enhanced SIMS (GESIMS) (pending European patent application no. EP 16461554.4), which allows for the precise estimation of the realistic distribution of dopants and contamination in graphene. In addition, we present evidence that the GESIMS effect leads to unexpected mass interferences with double-ionized species, and that these interferences are negligible in samples without graphene. The GESIMS method also shows that graphene transferred from Cu results in increased copper contamination.

Graphene Enhanced Secondary Ion Mass Spectrometry (GESIMS)

The following invention - Graphene Enhanced Secondary Ion Mass Spectrometry - (pending European patent application no. EP 16461554.4) is related to a method of analysing a solid substrate by means of Secondary Ion Mass Spectrometry (SIMS). It comprises the steps of providing a graphene layer over the substrate surface and analysing ejected secondary anions through mass spectrometry analysis. The graphene layer acts as a kind of filament that emits a lot of secondary electrons during the experiment which significantly increases the negative ionization probability and thus the intensity of the SIMS signal can be more than two orders of magnitude higher than that of a similar sample without graphene. The method is particularly useful for the analysis of surfaces, 2D materials and ultra-thin films. The intensity of dopants and contamination signals can be enhanced up to 35 times, which approaches the detection limit of ~1015atoms/cm3, otherwise unreachable in a standard static SIMS analysis.

Understanding of CO2 interaction with thermally grown SiO2 on Si using IBA depth profiling techniques

Interactions between CO2 and SiO2 films thermally grown on Si have been studied using 18O and 13C as isotopic tracers associated with ion beam analysis (IBA) depth profiling techniques. From secondary ion mass spectrometry (SIMS) measurements no carbon from CO2 is detected in the silica while it is found in Si. These results suggest that CO2 diffuses through the silica. Exchanges of oxygen between CO2 and silica can be observed from 18O to 16O SIMS signals variation. The oxygen concentration depth profiles were determined quantitatively using the narrow resonance near 151keV in the 18O(p,α)15N nuclear reaction (Narrow Resonance Profiling, NRP). We demonstrate that two distinct oxygen exchanges processes co-exist and we determine the diffusion coefficient of the CO2 molecule in the silica at 1100°C.

Enhancing the Sensitivity of Molecular Secondary Ion Mass Spectrometry with C60+-O2+ Cosputtering

In the past decade, the C60-based ion gun has been widely utilized in the secondary ion mass spectrometry (SIMS) analysis of organic and biological materials because molecular secondary-ions of high masses could be generated by cluster-ion bombardment. This technique furthers the development of SIMS in bioanalysis by eliminating the need for either heteroatom or isotope labeling. However, the intensity of high-mass parent ions was usually low and limited the sensitivity of the analysis, thus requiring an enhancement in the intensity of these molecular ions to widen the application of SIMS. In this work, the aim was to preserve samples in their original state while using a low kinetic energy O2(+) beam cosputtered with high-energy C60(+) to enhance the ion intensity through the depth-profile. Although O2(+) is generally used to enhance ion intensities in positive SIMS, it is known to alter the chemical structure and primarily provide elemental information; hence, it is not suitable for profiling organic and biological specimens. Nevertheless, owing to its high sputtering yield, cluster C60(+) ion removes and masks the structural damage, hence O2(+) may be used to enhance the ion intensity. The characteristic molecular ions of polyethylene terephthalate (PET), trehalose, and a peptide (papain inhibitor) are enhanced by 35×, 12×, and 3.5× with the use of the auxiliary O2(+) beam, respectively. This significant enhancement in ionization yield is attributed to the oxidation of molecules and formation of a hydroxyl group that serves as a proton donator. In addition to enhancing molecular SIMS signals, C60(+)-O2(+) cosputtering could also alleviate several problems, including sputtering rate decay, carbon deposition, and surface roughening, that are associated with C60(+) bombardment and produced better depth profiles.

BSA adsorption on titanium: ToF-SIMS investigation of the surface coverage as a function of protein concentration and pH-value

The adsorption properties of bovine serum albumin (BSA) on pure titanium (99.99%+) were studied by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). For this purpose, films consisting of BSA were prepared on cleaned titanium sheets in a phosphate buffered solution under different conditions and analysed by ToF-SIMS. The dependence of the surface coverage on the concentration of the protein solution could be determined from the secondary ion mass spectrometry signals. The results agree satisfactorily with the corresponding results obtained by XPS. The observed adsorption behaviour can be fitted by the well-known formula describing a Langmuir isotherm. The Langmuir constant for pH 7 was found to be K = 174 ± 99 lg(-)1.

Measurement of the redistribution of arsenic at nickel silicide/silicon interface by secondary ion mass spectrometry: artifact and optimized analysis conditions

The arsenic redistribution after NiSi formation has been measured by secondary ion mass spectrometry (SIMS). The NiSi film has been obtained by solid state reaction of a Ni thin film with a silicon substrate doped with As. An increase in the As SIMS signal at the NiSi/Si interface was observed for some experimental conditions. By varying the SIMS experimental parameters (incidence angle and the impact energy), the As signal at NiSi/Si interface was found to change. The SIMS experimental parameters have been optimized and were found to be an impact energy of 1 keV and an incidence angle superior to 50°. This allows us to minimize differences in sputtering rate and ion yield between NiSi and Si and to obtain a good depth resolution and dynamic range. Under these conditions the bump in the As signal does not appear: this illustrates the difficulty to measure concentration at interface by SIMS.

Oxidation-Assisted Secondary Ion Mass Spectrometry Methodology to Quantify Mixed Alkylthiol Self-Assembled Monolayers on Gold: Applications to Competitive Chemical Adsorption

A novel ozone oxidation assisted secondary ion mass spectrometry (SIMS) methodology was developed. The method provides a direct and simple approach to quantify mixed alkylthiol self-assembled monolayers (SAMs) on gold with higher detection sensitivity. Ozone oxidation of alkylthiol SAMs on gold causes the rupture of thiol−gold covalent bonds and the conversion of alkanethiolate to alkyl sulfonate. With negative ion SIMS measurement, the secondary ion yields of alkyl sulfonate are much higher than those of any molecular ions which originate from covalently bound alkylthiols. Using the intensity of molecular ions originating from intact alkyl sulfonate molecules from oxidized mixed SAMs to quantify the original mixed SAMs on gold can improve detection sensitivity. In this paper, we report results on the optimization of conditions for ozone oxidation of mixed alkylthiol SAMs on gold. Optimization using a combination of X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry data demonstrated that a small amount of oxidation was sufficient to produce strong SIMS signals to quantify the composition of mixed alkylthiol SAMs on gold. We applied the optimized method to a case study of steric effects on competitive chemical adsorption of alkylthiols to gold. The results from the case study indicated that by conversion of alkanethiolate to alkyl sulfonate using ozone oxidation pretreatment, mixed SAMs on gold can be straightforwardly quantified by SIMS analysis. Further, steric effects controlling the relative adsorption probability and surface coverage of a component from a mixture can be quantified. The competitive adsorption probabilities with respect to 1-decanethiol are 0.2 for 1-butanethiol, 5 × 10-3 for 1-methyl-1-propanethiol, and 9 × 10-4 for 2-methyl-2-propanethiol. The molar concentration ratio that is needed to form 1:1 mixed short/long SAMs is 5:1 for 1-butanethiol/decanethiol, 200:1 for 1-methyl-1-propanethiol/decanethiol, and 1000:1 for 2-methyl-2-propanethiol/decanethiol.

Preparation of oxycarbonate (Ba xSr 1- x) 2CuO 2(CO 3) epitaxial films by molecular beam epitaxy

Copper oxycarbonate thin films of (Ba x Sr 1- x ) 2CuO 2(CO 3) have been prepared on SrTiO 3(001) by molecular beam epitaxy using NO 2 gas as an oxidant and CO 2 gas. The films have been grown at 350∼500 °C. At high substrate temperature or at low CO 2 pressure, (Ba x Sr 1- x ) 2CuO 3 was formed instead of (Ba x Sr 1- x ) 2CuO 2(CO 3), and the films became amorphous at low temperature. X-Ray diffraction and reflection high-energy electron diffraction observations indicated that (Ba x Sr 1- x ) 2CuO 2(CO 3) grows along the [001] crystal orientation on SrTiO 3(001) with the following epitaxial relationship: (Ba x Sr 1- x ) 2CuO 2(CO 3)[100]//SrTiO 3[110] and (Ba x Sr 1- x ) 2CuO 2(CO 3)[110]//SrTiO 3 [100]. The depth profile of secondary ion mass spectrometry signals indicated the incorporation of carbon into the films. Electrical measurements showed that the as grown films exhibit a semiconducting behavior.

Freshwater bivalve shells as archival indicators of metal pollution from a copper-uranium mine in tropical northern Australia.

Freshwater bivalves (Velesunio angasi) were sampled in 1996 from the Finniss River in tropical northern Australia at 10 sites a priori exposed and nonexposed to acid rock drainage (ARD), containing elevated metal concentrations, from the rehabilitated Rum Jungle copper-uranium mine. Secondary ion mass spectrometry (SIMS) was used to measure Cu, Mn, Zn, U, Ni, Co, Pb, and Fe/Ca ratios across the annual shell laminations of the longest-lived bivalves found at each site, with the aim of evaluating the ability of the shells to archive measured annual metal inputs and their temporal patterns. At sites not contaminated by ARD, relatively constant and similar (baseline) SIMS signals were found for all metals in the shell laminations of V. angasi, dating as far back as 1965. At sites contaminated by ARD, relatively constant, but variably elevated, SIMS signals were evident for Cu, Mn, Zn, Ni, and Co in the shell, which extended back to the end of rehabilitation (1986) only. Since rehabilitation, the temporal patterns of Cu, Zn, and Mn observed in the shells at the most contaminated sites reflected those of the measured annual dissolved loads in the surface waters. The average concentrations of Cu, Mn, Zn, Ni, and Co in the shells decreased (3-13-fold) with increasing distance downstream of the mine site, until concentrations characteristic of the noncontaminated sites were reached. This geographic pattern of decline in pollution signal in the shell with increasing distance downstream of the pollution input is consistent with the pattern established for water and sediment chemistry. Overall, the SIMS results support the proposition that the shells of V. angasi can be used as archival indicators of metal pollution in surface waters of the Finniss River over their lifetime.

Solubility and diffusion of cobalt in alumina

Abstract Diffusion of Co in alumina was carried out between 1403 and 1873 K in air with or without the presence of a spinel phase. The penetration profiles were obtained by the secondary-ion mass spectrometry (SIMS) technique and at the highest temperature by tracer measurement. The Arrhenius relation D(1403-1873K) = 6.2 × 109exp (-333kJmolminus;1) m2 sminus;1/RT describes the temperature dependence of the diffusion coefficient obtained by both methods. The formation of the spinel phase CoAl2O4 was observed when the experiments were carried out at temperatures lower than 1673 K. The formation of the spinel phase offered a good opportunity to calibrate the SIMS signal and the solubility of Co in alumina was found to be about (2–4) × 10minus;3 metal atom fraction in the temperature range 1403–1623 K.

Solubility and diffusion of cobalt in alumina

Abstract Diffusion of Co in alumina was carried out between 1403 and 1873 K in air with or without the presence of a spinel phase. The penetration profiles were obtained by the secondary-ion mass spectrometry (SIMS) technique and at the highest temperature by tracer measurement. The Arrhenius relation D(1403-1873K) = 6.2 × 109exp (-333kJmolminus;1) m2 sminus;1/RT describes the temperature dependence of the diffusion coefficient obtained by both methods. The formation of the spinel phase CoAl2O4 was observed when the experiments were carried out at temperatures lower than 1673 K. The formation of the spinel phase offered a good opportunity to calibrate the SIMS signal and the solubility of Co in alumina was found to be about (2–4) × 10minus;3 metal atom fraction in the temperature range 1403–1623 K.

Preparation of [Ba2CuO2(CO3) ]m[ACuO2]n(A=Sr,Ca) Films by MBE Technique

ABSTRACT[Ba2CuO2(CO3)]m[ACuO2]n(A=Sr) superlattices containing oxycarbonate blocks as charge reservoir have been prepared on SrTiO3 using the molecular beam epitaxy technique. First, thin films of the oxycarbonate cuprate Ba2CuO2(CO3) have been prepared on SrTiO3(001) using NO2 gas as an oxidant and CO2 gas. The films have been grown at 500°C. At higher substrate temperature or at lower CO2 pressure Ba2CuO3 was formed instead of Ba2CuO2(CO3), and the films becomes amorphous at lower temperature. X-ray diffraction and reflection high-energy electron diffraction observations indicated that (BaxSr1−x)2CuO2(CO3) grew along the [001] crystal orientation on SrTiO3(001) with the following epitaxial relationship: Ba2CuO2(CO3)[100]//SrTiO3[110] and Ba2CuO2(CO3)[110]//SrTiO3 [100]. Depth profile of secondary ion mass spectrometry signals indicated the incorporation of carbon into the films. Secondly, the oxycarbonate cuprates and infinite layers have been alternately stacked. It was confirmed that Ba2CuO2(CO3)was inserted between several unit cells of SrCuO2. Electrical measurements show the as grown films to have a semiconducting behavior.

SIMS characterization of thin layers of IR and its silicides

To apply Secondary Ion Mass Spectrometry (SIMS) to the characterization of very thin films one needs to quantify the ionic intensity signals in non-steady-state conditions, that is, when the bombardment induced atomic mixing layer is not yet completely developed. Unfortunately, there is not enough information available about the complex stabilization processes taking place when analyzing thin films of iridium silicides by SIMS. We present data for the quantitation of SIMS signals taken from these silicides and the process that we have followed to obtain and to apply them. We begin with the characterization of thick silicide layers paying special attention to the signal behavior at their interfaces, and proceed to thinner layers. Some effects related to the presence of native intermixing layers are also shown.

Redistribution of constituent elements in Pd/Ge contacts to n-type GaAs using rapid thermal annealing

Pd/Ge contact to n-type GaAs is performed by using electron-beam evaporation and rapid thermal annealing. The rapid thermal annealing is performed at 400–500 °C for various time durations. Low specific contact resistivity on the order of 10−6 Ω cm2 is obtained from measurements based on the transmission line model method. The contact depth profiles are analyzed by secondary ion mass spectrometry (SIMS). A very shallow ohmic contact is achieved. The redistribution of constituent elements after heat treatment is examined. A gallium SIMS signal bump is detected in the contact layer and is correlated with good ohmic contact behavior. A model based on Ga vacancies is proposed to explain this phenomenon. This shallow ohmic contact technology has been successfully utilized to fabricate GaAs/AlGaAs and GaAs/InGaAs/AlGaAs negative resistance field-effect transistors, for which shallow ohmic contact is critical.

Pd/Ge ohmic contacts to n-type GaAs formed by rapid thermal annealing

Pd/Ge ohmic contact to n-type GaAs is obtained by using the rapid thermal annealing (RTA) method. The best specific contact resistivity of ohmic contacts annealed at 400–500 °C is on the order of 10−6 Ω cm2. Secondary ion mass spectrometry (SIMS) measurement shows that these ohmic contacts are very shallow. Gallium dissociation from GaAs is observed. It is found that there is a correlation between a gallium SIMS signal bump and good ohmic contact behavior. A model is proposed for this phenomenon. This RTA ohmic contact method has been successfully applied to the fabrication of charge injection transistor/negative resistance field-effect transistor devices.

Hydrogen and deuterium desorption kinetics from silicon(100) 2*1 studied using SIMS

Secondary ion mass spectrometry (SIMS) operating with primary ion current density (J<5*10-8 A cm-2) was used to study the desorption process of hydrogen and deuterium from silicon(100). The description of the desorption process of hydrogen and deuterium was obtained monitoring the H+ and D+ SIMS signals as a function of the annealing temperature and annealing time. Low-energy electron diffraction (LEED) measurements enabled the surface coverage to be identified as monohydride or dihydride phases. The desorption of both elements displayed second-order kinetics. In addition, the process of reaction between hydrogen and deuterium adsorbed at different temperatures was studied.