Secondary Neutral Mass Spectrometry Research Articles

Effects of vacuum and ageing on Zr4/Cr3 based conversion coatings on aluminium alloys

In this study, we investigate the impact of ageing and high vacuum on existing environmentally friendly Zr4/Cr3-based conversion coatings. The freshly formed coating undergoes several changes during ageing and exposure to high vacuum. Based on the present data, we propose that the coating formed over AA6082 and AA7075 alloys is sol-gel in nature, confirmed by secondary neutral mass spectroscopy (SNMS) using the depth profiling technique. Our findings reveal that there are elemental level changes that result in shrinkage of the coating. Most Zr ions in the coating are in the solute form, with lesser number of Cr and Al ions that disappear under high vacuum over a certain period of time. The remaining Cr, Zr and O atoms exist in a gelatinous state. During ageing, there is a continuous transition of ions from solute to gelatinous state. In addition, the deposition of coating ions is directly influenced by the substrates and their constituents. The extent of dissolution of aluminium in the conversion bath determines both Zr and Cr ion deposition. For a highly alloyed metal like AA7075, the dissolution rate is disturbed by copper and zinc.

The transition from linear to-parabolic growth of Cu3Si phase in Cu/a-Si system

The solid state reaction between Cu and a-Si films was investigated at 150–200°C by depth profiling with secondary neutral mass spectrometry. Intermixing was observed leading to the formation of a homogeneous Cu3Si layer at the interface. The growth of the crystalline silicide follows a parabolic law at 165°C and 200°C. At 150°C a transition from linear to parabolic kinetics is observed. Combining with our previous experimental results showing linear kinetics at 135°C [Acta Materialia, 61 (2013) 7173–7179], the temperature dependence of the linear and parabolic coefficients as well as the transition length can be estimated.

On the miscibility gap of Cu-Ni system

The existence of the miscibility gap in the Cu-Ni system has been an issue in both computational and experimental discussions for half a century. Here we propose a new miscibility gap in the Cu-Ni system measured in nano-layered films by Secondary Neutral Mass Spectrometry. The maximum of the symmetrical miscibility curve is around 780K at Cu50%Ni50%. This is the first experiment determining the miscibility from the measurement of the atomic fraction of Copper and Nickel in the whole composition range.

Implementation and Optimization of Large Gas Cluster Laser Post-Ionization Secondary Neutral Mass Spectrometry for Molecular Analysis

In this study, we describe for the first time a new combined technique for molecular surface analysis using large argon gas clusters as primary ions for laser postionization secondary neutral mass spectrometry (Laser-SNMS). This new technique was investigated on polymer polystyrene (PS) surfaces using pulsed Ar2000+ ions with 20 keV energy and a 157 nm laser beam for postionization. To optimize the ion yield, time-of-flight (ToF) distributions of characteristic sputtered neutral PS fragments were determined. The data could be fitted well with Maxwell–Boltzmann distributions. The data show that the maxima of the individual ToF distributions of the sputtered neutrals move to higher delay time values with increasing mass, which directly correlates to a decrease of velocity of the sputtered neutrals with increasing mass. The delay time dependence on mass could be fitted with a quadratic curve, thus indicating a constant mean kinetic energy for the sputtered molecules. The ion yields obtained with large gas cl...

Formation of the Sputtered Phase of PbTe Crystals by Ar+ Plasma and Re-deposition of the Sputtered Species at Secondary Neutral Mass Spectrometry Conditions

Formation of the Pb and Te sputtered phase under exposure of the lateral surface of PbTe crystals grown from melt by the Bridgman method by Ar+ plasma at Secondary Neutral Mass Spectrometry (SNMS) conditions and re-deposition of the sputtered species on the sputtering crystal surface are investigated. Experimental evidence of mutual influence of the sputtering and re-deposition processes on each other during prolonged depth profiling of PbTe crystals is presented. Sputtering of the PbTe crystal surface forms the strongly supersaturated sputtered phase of Pb and Te. Re-deposition of the Pb and Te sputtered atoms on the crystal surface results in oscillations of sputtering rate of PbTe crystal and changes of average intensity of Pb and Te sputtering over sputtering time. A possible role of both the sub-critical nuclei of newly re-deposited phase and the re-deposited surface structures of post-critical sizes in generation of the features of PbTe crystal sputtering is discussed. It is concluded that formation and re-sputtering of the sub-critical nuclei of re-deposited phase leads to the oscillations of sputter yields of Pb and Te. Growth and re-sputtering of the re-deposited surface structures of post-critical sizes lead to changes of average values of Pb and Te sputter yields.

Effect of Yttrium as Alloying Element on a Model Alumina-Forming Alloy Oxidation at 1100 °C

In order to study the effect of yttrium as alloying element on the high-temperature oxidation of an alumina-forming alloy, 0.093 wt% yttrium was incorporated into a model FeCrAl alloy. Yttrium has a beneficial effect on the isothermal oxidation behavior in air at 1100 °C. Glancing angle X-ray diffraction made on a sample oxidized for 1000 h under thermal cycling conditions indicated that yttrium is located at the internal interface as Y3Al5O12. Secondary neutral mass spectrometry results showed that the diffusion mechanism is modified by the presence of yttrium as an alloying element. Moreover, the beneficial effect of yttrium on the alloy oxidation is also related to a reduced metallic grain size. The growth of metal grains during oxidation was especially observed on the yttrium-free FeCrAl alloy. It is also well established that the diffusion mechanism in the oxide scale is modified by yttrium. The aim of the present work was to show that yttrium also plays a role on the aluminum diffusion in the metallic substrate and has a strong influence on the kinetic transient stage during the FeCrAl–0.1Y oxidation.

Interface Crystallization of Ceria in Porous Silica Films for Solar Applications

Antireflective (AR) coatings with photocatalytic activity for solar cover glasses are extensively investigated at present, mostly in multilayer systems including titania. In this study, bifunctional single coats from porous silica in combination with up to 33 mol % ceria were prepared by sol–gel dip-coating on low-iron soda-lime float glass. After heat treatment for one hour at 350 °C, the coated glasses were characterized. Solar transmittance decreased with increasing ceria content, whereas photocatalytic activity increases. Crystallization of cubic ceria was detected by grazing incidence X-ray diffraction. Chemical depth profiling by secondary neutral mass spectrometry revealed the enrichment of cerium at the coating surface as well as at the interface to the glass substrate. Self-assembled ceria crystallization at the interfaces resulted in a three-layered mesostructure of the coating, which was verified by field-emission scanning electron spectroscopy. Cubic ceria crystals at the interface act as a barrier for the sodium diffusion from the substrate, which prevents the poisoning of the photocatalyst, while those crystals at the surface act as an electron donor for photooxidation processes, both enabling adequate photocatalytic activity. The triple-layer architecture with the sequence of high/low/high refractive index materials allows for optical interference sustaining the AR-function.

On the mechanisms of hydrogen-induced blistering in RF-sputtered amorphous Ge

Hydrogenated amorphous germanium, a-Ge:H, is a material of interest for optoelectronic applications such as solar cells and radiation detectors because of the material's potential to extend the wavelength sensitivity of hydrogenated amorphous silicon. For such applications, the best structural quality is required. Here, we investigate the mechanisms of blister formation in a-Ge:H films obtained by RF (radio frequency) sputtering when submitted to annealing. By a Fourier transform IR spectroscopy study of the Ge–H stretching vibrations, it is found that annealing increases the density of GeH2 dihydrides residing on the internal surfaces of nanovoids which increase their size because of that. The thermal energy supplied by annealing also favours the breakage of the Ge–H bonds with consequent release inside the cavities of atomic H which then reacts to produce molecular H2. The expansion of the H2 gas causes the nanovoids to enhance their volume up to the formation of surface blisters. The presence of H2 in the blisters is confirmed by the activation energy for the onset of blistering as measured by Arrhenius plots. The reduced H content observed by elastic recoil detection analysis and secondary neutral mass spectrometry in the annealed samples where blister bursting took place further supports the hypothesis of H2 filling the blisters before they explode.

Impact of Corrosive Liquid on Trivalent Chromium over Aluminium Alloys

Considering aviation and space sectors, aluminium alloys are commonly used due to its excellent mechanical and physical properties. Though satellite hard-ware is confined to controlled environment, it requires anticorrosive treatment over metal substrate followed by a systematic coating scheme. The trivalent chromium coating was deposited over three aluminium alloys namely AA6063, AA7075 and AA6082. The variation in corrosion resistance property of trivalent chromium over each aluminium alloy has been studied in detail. The Neutral Salt Spray (NSS) test result shows that trivalent chromium coating over AA7075 alloy is affected by pitting corrosion compared to other two alloys. In addition to that, NSS test also proves that thickness of the layer does not have any influence corrosion resistance property of trivalent chromium coating. Furthermore, ions in trivalent chromium coating was identified using Secondary Neutral Mass Spectroscopy (SNMS) and degradation of coating in a corrosive liquid studied using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) instrument to understand mechanism of corrosion. The results indicated that both coating and substrate is involved in corrosion process. The number of elements dissolved in to salt solution reveals the weak ionic bonding of coating towards substrates. In comparison, AA7075 alloy has weaker bonding than AA6082 and AA6063 series. The alloying elements such as zinc and copper are removed from substrate by corrosive solution.

Coloring hot-dip galvanization of steel samples in industrial zinc-manganese baths

Colored hot dip galvanization of various steel samples was realized in an industrial bath containing 738 kg of a Zn-Mn liquid alloy at 450?C. Zinc was alloyed in three steps to reach 0.1, 0.15 and 0.2 w% of Mn in liquid zinc, and galvanization of 9 different steel samples was performed in all three baths. The obtained colors change in the sequence blue - yellow - pink - green with increasing the Mn-content of the bath and with increasing the wall thickness of the steel samples. The results are analyzed by Glow-discharge optical emission spectroscopy (GD-OES) and Secondary Neutral Mass Spectrometry (SNMS) techniques. It is shown that depending on the Mn-content and on the wall thickness of the steel the samples are coated by MnO of various thicknesses (in the range between 30 - 230 nm). This layer forms when the samples are removed from the Zn-Mn bath into surrounding air, before the Zn-layer is solidified. Light interference on this thin MnO layer causes the colors of the galvanized coating. Different colors are obtained in different ranges of MnO thicknesses, in accordance with the laws of optics. The minimum Mn-content of liquid Zn is found as 0.025 ? 0.010 m/m% to ensure that the original outer ZnO layer on Zn is converted into the MnO layer. This minimum critical Mn-content is in agreement with chemical thermodynamics.

Surface chemistry evolution of F‐doped Ni‐base superalloy upon heat treatment

Ni‐based superalloys with Al‐contents between 3 and 5 wt% exhibit insufficient oxidation resistance at temperatures above 900 °C. A change of the oxidation mechanism has been achieved after doping surface‐near regions with fluorine by ion implantation and subsequent heat treatment. With that, the formation of a protective alumina scale was observed. This study is dedicated to the nature of the kinetic bias for the alumina scale formation. The samples of alloy IN738 (3.5 wt% Al) were implanted with F‐ions (1017 F/cm2 at 38 keV). The depth profiles of O, Ni, Cr, Co, Ti, and Al were determined using secondary neutrals mass spectrometry (SNMS), whereas the F‐depth profiles were measured by non‐destructive proton‐induced gamma‐ray emission (PIGE). Directly after F‐implantation no Al‐enrichment near the surface was observed. After heating up to temperatures between 400 and 800 °C, no distinct alumina scale formation was observed. At 1000 and 1050 °C, a distinct Al‐rich region has formed. Extending the oxidation time up to 12 h leads to a pronounced Al‐profile, suggesting the growth of a pure alumina scale near the surface.

Angular Distribution of Molecules Sputtered by Gas Cluster Ion Beams and Implications for Secondary Neutral Mass Spectrometry

We present experimental data on the angular distribution of Irganox 1010 organic molecules sputtered by large argon gas cluster projectiles (E/n = 5 eV, 10 keV Ar2000). Ejection probability distributions as derived from deposit patterns on planar collector surfaces were recorded at various angles of incidence of the primary cluster ion beam. The sputtered material is ejected at polar angles, on average, greater than 45° from the surface normal. At normal incidence there is no azimuthal dependence in the ejecta distribution, but the ejecta are forward directed even at incidence angles as low as 15°. After this initial rapid change, the ejecta distribution shows a rather weak dependence on the incidence angle of the primary ion beam and the polar, and azimuthal angles of preferred ejection remain relatively constant. Ejecta distributions agree with previously published results from molecular dynamics simulations for organic molecules sputtered with large argon gas cluster projectiles and are consistent with...

Improved 3D-imaging of a sirolimus/probucol eluting stent coating using laser postionization secondary neutral mass spectrometry and time-of-flight secondary ion mass spectrometry

Implantable drug delivery systems that provide controlled and sustained release of a therapeutic agent are used in a wide variety of applications. Drug eluting stents, which are used to treat coronary artery disease, are among the most widespread of these devices, with an estimated 3 × 106 implants annually worldwide. Controlling the rate of drug release from these devices relies on precise control of the three dimensional (3D)-distribution of the drug, so methods for measuring this distribution are of great importance. The aims of this work were to determine how 3D-imaging of polymer-free sirolimus/probucol drug eluting stent coatings could be improved through the use of laser postionization secondary neutral mass spectrometry (Laser-SNMS) and Ar cluster sputtering with time-of-flight secondary ion mass spectrometry (ToF-SIMS) and to optimize conditions for this analysis. In this study, 3D-imaging of a sirolimus/probucol dual drug eluting stent has been investigated using Laser-SNMS and ToF-SIMS. Laser-SNMS studies of pure sirolimus and probucol were undertaken using 30 keV Bi3+ primary ions and a 157 nm excimer postionization laser. Under optimal conditions, a greater than 100-fold increase in detected ion yield was observed for Laser-SNMS when compared to ToF-SIMS, although ToF-SIMS provided equal or greater yields for higher mass characteristic ions. Although the optimal laser power density for detecting probucol (5 × 106 W/cm2) was significantly lower than the optimum for sirolimus (7 × 107 W/cm2), an intermediate laser power density of 1 × 107 W/cm2 was sufficient to allow imaging of both drugs. Using individual selected ion signals, ToF-SIMS and Laser-SNMS produced similar images of the two drug species. When using, however, a multivariate approach (maximum autocorrelation factors), Laser-SNMS provided significant improvements in image contrast and small area detection when compared to ToF-SIMS. Following optimization of the technique, 3D-images of the dual drug eluting stent coating were obtained using 10 keV Ar2000+ cluster ions for sputtering and 30 keV Bi3+ cluster ions for analysis for both ToF-SIMS and Laser-SNMS. This work demonstrates the advantages of Laser-SNMS for 3D-imaging of pharmaceutical devices, which has not been previously published. Both ToF-SIMS and Laser-SNMS revealed that the outermost surface of the drug eluting coating contained pure sirolimus to a depth of a few tens of nanometers, with a few channels of sirolimus extending to a depth of around 1 μm. Below about 1 μm, the two drugs were uniformly mixed. Using the 10 keV Ar2000+ sputter beam, the authors were able to sputter through the complete drug coating (∼6 μm) without observing any accumulated damage in the organic layer. The two techniques showed complementary strengths: ToF-SIMS offers faster data collection and better detected ion yield for larger characteristic ions than Laser-SNMS, and Laser-SNMS offers significantly enhanced detected ion yield for smaller fragment ions, allowing for improved image contrast and resolution of smaller features.

ToF-SIMS and Laser-SNMS Imaging of Heterogeneous Topographically Complex Polymer Systems.

Heterogeneous polymer coatings, such as those used in organic electronics and medical devices, are of increasing industrial importance. In order to advance the development of these types of systems, analytical techniques are required which are able to determine the elemental and molecular spatial distributions, on a nanometer scale, with very high detection efficiency and sensitivity. The goal of this study was to investigate the suitability of laser postionization secondary neutral mass spectrometry (Laser-SNMS) with a 157 nm postionization laser beam to image structured polymer mixtures and compare the results with time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements using Bi3+ primary ions. The results showed that Laser-SNMS is better suited than ToF-SIMS for unambiguous detection and submicrometer imaging of the wide range of polymers investigated. The data also showed that Laser-SNMS has the advantage of being much more sensitive (in general higher by more than an order of magnitude and peaking at up to 3 orders of magnitude) than ToF-SIMS while also showing superior performance on topographically complex structured insulating surfaces, due to significantly reduced field effects and a higher dynamic range as compared to ToF-SIMS. It is concluded that Laser-SNMS is a powerful complementary technique to ToF-SIMS for the analysis of heterogeneous polymers and other complex structured organic mixtures, providing submicrometer resolution and high sensitivity.

Morphology of PbTe Crystal Surface Sputtered by Argon Plasma under Secondary Neutral Mass Spectrometry Conditions

We have investigated morphology of the lateral surfaces of PbTe crystal samples grown from melt by the Bridgman method sputtered by Ar+ plasma with ion energy of 50 – 550 eV for 5 - 50 minutes under Secondary Neutral Mass Spectrometry (SNMS) conditions. The sputtered PbTe crystal surface was found to be simultaneously both the source of sputtered material and the efficient substrate for re-deposition of the sputtered material during the depth profiling. During sputtering PbTe crystal surface is forming the dimple relief. To be re-deposited the sputtered Pb and Te form arrays of the microscopic surface structures in the shapes of hillocks, pyramids, cones and others on the PbTe crystal sputtered surface. Correlation between the density of re-deposited microscopic surface structures, their shape, and average size, on the one hand, and the energy and duration of sputtering, on the other, is revealed.

Method for a High-Rate Solution Deposition of Zn(O,S) Buffer Layer for High-Efficiency Cu(In,Ga)Se2-Based Solar Cells

We present a method for high-rate solution growth of the Zn(O,S) buffer layer to achieve deposition rates and material consumptions far below the standard Zn(O,S) and CdS deposition method. We replace the organosulfide thiourea by the more quickly decomposable thioacetamide and control the reaction kinetics by the use of chelating ligands and ammonia. We characterize the produced layers by secondary neutral mass spectrometry, X-ray diffraction, and optical transmission. For cell preparation, we use high-efficiency Cu(In,Ga)Se2 with an alkali-modified surface, as well as industrially relevant inline absorber material. We realize a certified 21% cell efficiency with the standard thiourea-based Zn(O,S) and first cells with over 19 % with the high-rate Zn(O,S) buffer.

Quantitative depth profiling of Si1–xGex structures by time-of-flight secondary ion mass spectrometry and secondary neutral mass spectrometry

Quantification of Ge in Si1–xGex structures (0.092≤x≤0.78) was carried out by time-of-flight secondary ion mass spectrometry (TOF-SIMS) and electron-gas secondary neutral mass spectrometry (SNMS). A good linear correlation (R2>0.9997) of the intensity ratios of secondary ions GeCs2+/SiCs2+ and 74Ge−/30Si− and post-ionized sputtered neutrals 70Ge+/28Si+ with Ge concentration was obtained. The calibration data were used for quantitative depth profiling of [10×(12.3nm Si0.63Ge0.37/34nm Si)] structures on Si. Satisfactory compliance of the quantified Ge concentration in SiGe layers with the values obtained by high-resolution X-ray diffraction was revealed for both techniques. SIMS and SNMS experimental profiles were fitted using Hofmann's mixing-roughness-information depth (MRI) model. In the case of TOF-SIMS, the quality of the reconstruction was better than for SNMS since not only the progressing roughening, but also the crater effect and other processes unaccounted in the MRI simulation could have a significant impact on plasma sputter depth profiling.

Secondary ion and neutral mass spectrometry with swift heavy ions: Organic molecules

The authors report on experiments regarding the electronic and nuclear sputtering of organic films. The newly built swift heavy ion induced particle emission and surface modifications setup [Meinerzhagen et al., Rev. Sci. Instrum. 87, 013903 (2016)] at the M1 Branch at the universal linear accelerator (UNILAC) beam line at GSI in Darmstadt, Germany, has been used for research on organic molecules in the electronic sputtering regime. This setup has the unique capability not only to investigate electronically sputtered ions by projectiles with kinetic energies up to several giga-electron-volt but also to detect their neutral counterparts as well by laser postionization. For this purpose, the experiment is equipped with a laser system delivering 157 nm pulses with photon energies of 7.9 eV to be utilized in single photon ionization. In addition to the investigation of sputtered ions and neutrals in the electronic sputtering regime, a comparison of typical fragments between fundamentally different sputtering mechanisms has been performed by using two different common time of flight secondary ion mass spectrometry (SIMS) instruments. The use of the different instruments offers the possibility to investigate the influence of the differing sputter processes from the linear cascade regime over collisional spikes to the thermal spike regime under high energy ion bombardment. The experiments in the collision-dominated nuclear stopping regime have been performed using 20 keV Bi+ and Bi3+ as atomic and small cluster projectiles and using 20 keV C60+ representing a medium-sized cluster. In the electronic sputtering regime, 4.8 MeV/u 197Au26+ swift heavy ions created by the UNILAC have been used as projectiles. As targets thin films of coronene on silicon substrates, a polycyclic hydrocarbon and Irganox 1010, an antioxidant well known from different studies in the SIMS community, have been utilized.

Determination of the compositions of the DIGM zone in nanocrystalline Ag/Au and Ag/Pd thin films by secondary neutral mass spectrometry.

Alloying by grain boundary diffusion-induced grain boundary migration is investigated by secondary neutral mass spectrometry depth profiling in Ag/Au and Ag/Pd nanocrystalline thin film systems. It is shown that the compositions in zones left behind the moving boundaries can be determined by this technique if the process takes place at low temperatures where solely the grain boundary transport is the contributing mechanism and the gain size is less than the half of the grain boundary migration distance. The results in Ag/Au system are in good accordance with the predictions given by the step mechanism of grain boundary migration, i.e., the saturation compositions are higher in the slower component (i.e., in Au or Pd). It is shown that the homogenization process stops after reaching the saturation values and further intermixing can take place only if fresh samples with initial compositions, according to the saturation values, are produced and heat treated at the same temperature. The reversal of the film sequence resulted in the reversal of the inequality of the compositions in the alloyed zones, which is in contrast to the above theoretical model, and explained by possible effects of the stress gradients developed by the diffusion processes itself.

Oscillations and huge preferences of PbTe crystal surface sputtering under Secondary Neutral Mass Spectrometry conditions

Sputtering of PbTe crystals by Ar+ plasma with ion energies 50–550eV is investigated. A dependence of sputter yields of the Te and Pb on the sputtering ion energy and sputtering time is measured. New phenomena: aperiodical oscillations of Pb and Te sputtering; a huge preference of Te sputtering reaching more than two orders of magnitude at the beginning of sputtering process; and a significant excess of Te integrated sputter yield over that of Pb for prolonged sputtering by low energy plasma at 50–160eV, are observed. It is substantiated that these phenomena can be caused by the peculiarities of the charge states of the interstitial Pb and Te in PbTe crystal matrix and the processes of re-deposition of sputtered atoms on the sputtered surface.