Time-of-flight Secondary Ion Mass Spectrometry Results Research Articles

Compositional mapping of Mo-doped ZnO thin films: Mechanical, nano-surface and ToF-SIMS analyses

ZnO and Mo-doped ZnO thin films were grown using the spray pyrolysis process with variations in Mo doping concentrations. The films were characterized with a comprehensive compositional analysis, including electron dispersive X-ray (EDX), X-rays photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS), along with grazing incidence X-ray diffraction(GIXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV–Vis spectroscopy to investigate their structural, morphological, optical and chemical compositions. Micro-hardness analysis was performed on films as a function of the Mo content. GIXRD analysis detected the presence of characteristic peaks of ZnO along the (100), (002) and (101) planes. The presence of Zn, O, and Mo in the synthesized samples was revealed by EDX, XPS, and ToF-SIMS results, which matched the experimental values of a pure and Mo:ZnO-x composition. XPS analysis revealed the Mo6+ oxidation state of molybdenum present in Mo:ZnO films. From UV–Vis absorption spectroscopy, the bang gap was observed to increase with Mo content, up 5 at.%, and located in the 3.18 – 3.24 eV interval. These results will be helpful in the synthesis of Mo:ZnO films for relevant applications, including sensing, optoelectronics and antimicrobial.

Crystal face dependent wettability of α-quartz: Elucidation by time-of-flight secondary ion mass spectrometry techniques combined with molecular dynamics

HypothesisQuartz is one of the most common but important minerals, and its wettability plays a significant role in affecting various natural and industrial processes. Studies have revealed that different crystal faces of quartz are with different wettabilities, but its mechanism is still vague. Experiments and simulationsFor specifying the mechanism of crystal face dependent wettability, the contact angles of three different liquids on the crystal faces of α-quartz are measured; the time-of-flight secondary ion mass spectrometry (ToF-SIMS) is employed to establish the crystal surface models; molecular dynamics (MD) simulations with the surface models are performed to understand the wetting behavior at molecular scale. FindingsBased on the contact angle measurements, the wettabilities of different crystal faces of α-quartz are found different, which can be directly attributed to the concentration of hydroxyl group on crystal faces based on ToF-SIMS results. MD simulations yield consistent results with the contact angle order recognized from experiments, revealing that the surface hydroxyl group controls the wettability of α-quartz crystal faces. It is also recognized that the pristine surface atomic arrangement, especially the surface concentration of unsaturated bond (an intrinsic property of α-quartz), is the intrinsic cause of the difference in the concentration of hydroxyl group of the crystal surface.

Improved understanding of the sulfidization mechanism in cerussite flotation: An XPS, ToF-SIMS and FESEM investigation

Sulfidization can greatly improve the flotation performance of lead oxide minerals. To provide deeper knowledge about this process, sulfidization of cerussite was investigated using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and field emission electron microscopy (FESEM). XPS results clearly indicated a transformation of PbCO3 into PbS on the cerussite surfaces during sulfidization, which was consistent with ToF-SIMS results. Further, FESEM images showed that many nanoparticles grew on the cerussite at a high density, suggesting that the sulfidization product on the cerussite was not a monatomic layer but a solid polyatomic layer. The above results confirmed that PbS nanoparticles could grow on most of the surfaces of cerussite under flotation-related conditions, indicating that the sulfidized cerussite had a PbCO3/PbS core-shell structure. The formation of PbS nanoparticles on cerussite involved a heterogeneous nucleation step followed by growth of the nuclei. Based on these studies, a sulfidization process model was finally obtained.

Multitechnique elemental depth profiling of InAlGaN and InAlN films

This work shows the capabilities of the plasma profiling time of flight mass spectrometry (PP-TOFMS) for the determination of elemental composition and distribution in InAlGaN thin films used for high electron mobility transistors. The PP-TOFMS results have been compared with wavelength dispersive x-ray fluorescence analyses for the elemental composition determination and with x-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry (TOF-SIMS) for elemental distributions. Relative sensitivity factors have been developed for the comparison of PP-TOFMS with TOF-SIMS results. The PP-TOFMS was able to determine the relative composition of In and Al in the thin films with an accuracy of 10 rel. % without calibration. Depth profiles acquired from the PP-TOFMS technique were obtained within a few minutes and exhibited very similar In, Al, and Ga distributions to TOF-SIMS measurements, and thus PP-TOFMS has been shown to be a valuable addition to TOF-SIMS analysis for a fast process development.

Reduced dental calcium expression and dental mass in chronic sleep deprived rats: Combined EDS, TOF-SIMS, and micro-CT analysis

Teeth are the hardest tissue in the body. The growth of teeth is closely regulated by circadian rhythmicity. Considering that sleep deprivation (SD) is a severe condition that disrupts normal circadian rhythmicity, this study was conducted to determine whether calcium expression (the major element participating in teeth constitution), and dental mass would be significantly impaired following SD. Adolescent rats subjected to 3 weeks of SD were processed for energy dispersive spectrum (EDS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and micro-computed tomography (micro-CT) analyses. The EDS and TOF-SIMS results indicated that high calcium intensity was detected in both the upper and lower incisors of untreated rats. Micro-CT analysis corresponded closely with spectral data in which an enhanced dental mass was calculated in intact animals. However, following SD, both calcium expression and the dental mass were remarkably decreased to nearly half those of the untreated values. Because SD plays a detrimental role in impairing dental structure, establishing satisfactory sleep behavior would therefore serve as a crucial strategy for preventing or improving prevalent dental dysfunctions.

Surface initiated atom transfer radical polymerization grafting of sodium styrene sulfonate from titanium and silicon substrates.

This study investigates the grafting of poly-sodium styrene sulfonate (pNaSS) from trichlorosilane/10-undecen-1-yl 2-bromo-2-methylpropionate functionalized Si and Ti substrates by atom transfer radical polymerization (ATRP). The composition, molecular structure, thickness, and topography of the grafted pNaSS films were characterized with x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), variable angle spectroscopic ellipsometry (VASE), and atomic force microscopy (AFM), respectively. XPS and ToF-SIMS results were consistent with the successful grafting of a thick and uniform pNaSS film on both substrates. VASE and AFM scratch tests showed the films were between 25 and 49 nm thick on Si, and between 13 and 35 nm thick on Ti. AFM determined root-mean-square roughness values were ∼2 nm on both Si and Ti substrates. Therefore, ATRP grafting is capable of producing relatively smooth, thick, and chemically homogeneous pNaSS films on Si and Ti substrates. These films will be used in subsequent studies to test the hypothesis that pNaSS-grafted Ti implants preferentially adsorb certain plasma proteins in an orientation and conformation that modulates the foreign body response and promotes formation of new bone.

Probing the Orientation of β-Lactoglobulin on Gold Surfaces Modified by Alkyl Thiol Self-Assembled Monolayers

The adsorption of a globular protein on chemically well controlled surfaces was investigated in order to correlate its orientation to the surface properties. To this end, three different alkyl thiols, differing by their end group (-COOH, -CH3, and -NH2), were used to build up self-assembled monolayers (SAMs) on gold substrates. β-Lactoglobulin (βLG) was then adsorbed on these SAMs by immersion in a phosphate buffer solution. The surface modification with alkyl thiols and the subsequent adsorption of proteins were characterized ex situ by polarization modulated infrared reflection-absorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). The adsorption behavior of proteins was also monitored in situ using quartz crystal microbalance with dissipation measurements (QCM-D). Direct evidence regarding the protein orientation in the adsorbed state was obtained by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). Principal component analysis (PCA), performed on the ToF-SIMS results, enables to separate the samples and shows that the proteins display different distributions of amino acids at the surface depending on the conditioning thiol layer. Our results revealed that the adsorption mode of the protein is influenced by the thiol end groups, and specific orientations of the protein on the surface are proposed for the different substrates. © 2013 American Chemical Society.

Nisin adsorption on hydrophilic and hydrophobic surfaces: evidence of its interactions and antibacterial activity

Study of peptides adsorption on surfaces remains a current challenge in literature. A complementary approach, combining X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to investigate the antimicrobial peptide nisin adsorption on hydrophilic and hydrophobic surfaces. The native low density polyethylene was used as hydrophobic support and it was grafted with acrylic acid to render it hydrophilic. XPS permitted to confirm nisin adsorption and to determine its amount on the surfaces. ToF-SIMS permitted to identify the adsorbed bacteriocin type and to observe its distribution and orientation behavior on both types of surfaces. Nisin was more oriented by its hydrophobic side to the hydrophobic substrate and by its hydrophilic side to the outer layers of the adsorbed peptide, in contrast to what was observed on the hydrophilic substrate. A correlation was found between XPS and ToF-SIMS results, the types of interactions on both surfaces and the observed antibacterial activity. Such interfacial studies are crucial for better understanding the peptides interactions and adsorption on surfaces and must be considered when setting up antimicrobial surfaces.

In Situ Reactivity and TOF-SIMS Analysis of Surfaces Prepared by Soft and Reactive Landing of Mass-Selected Ions

An instrument has been designed and constructed that enables in situ reactivity and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of surfaces prepared or modified through soft and reactive landing of mass-selected polyatomic cations and anions. The apparatus employs an electrospray ion source coupled to a high transmission electrodynamic ion funnel, two focusing collision quadrupoles, a large 19 mm diameter quadrupole mass filter, and a quadrupole bender that deflects the ion beam, thereby preventing neutral contaminants from impinging on the deposition surface. The ion soft landing apparatus is coupled to a commercial TOF-SIMS instrument permitting the introduction of surfaces into vacuum and SIMS analysis before and after ion deposition without breaking vacuum. To facilitate a comparison of the current TOF-SIMS instrument with the in situ Fourier transform ion cyclotron resonance (FTICR-SIMS) deposition apparatus constructed previously, dications of the cyclic peptide Gramicidin S (GS) and the photoactive organonometallic complex ruthenium tris-bipyridine (Ru(bpy)(3)) were soft-landed onto fluorinated self-assembled monolayer (FSAM) on gold surfaces. In both cases, similarities and differences were observed in the secondary ion mass spectra, with the TOF-SIMS results, in general, characterized by greater sensitivity, larger dynamic range, less fragmentation, and fewer in-plume reactions than the corresponding FTICR-SIMS spectra. The charge reduction kinetics of both the doubly and singly protonated GS cations on the FSAM surface were also examined as was the influence of the primary gallium ion (Ga(+)) flux on the efficiency of these processes. In addition, we demonstrate that the new instrument enables detailed studies of the reactivity of catalytically active species immobilized by soft and reactive landing toward gaseous reagents.

Quantitative TOF-SIMS analysis of metal contamination on silicon wafers

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is one of the most promising candidates for high sensitivity surface analysis, in line with the requirements reported by the 1997 Semiconductor Industry Association (SIA) roadmap. However, the data quantification is not straightforward because of strong matrix effects and must be still completely developed. This work aims at obtaining TOF-SIMS calibration for the quantification of metals on oxidized silicon wafers. Standards with different amounts of various elements are prepared by dipping and spinning methods. TOF-SIMS results are compared with TXRF, VPD-AAS and other techniques. The required uniformity and reproducibility of the standards are discussed, as well as the TOF-SIMS experimental set-up and the sampling strategy for the comparison between different techniques.

Characterization of the surface organization of nanostructured hybrid organic-inorganic materials by time-of-flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been used to analyse the surface composition of organic-inorganic hybrid solids obtained by a sol-gel process. Gels of type O(1.5)Si-R-SiO(1. 5), obtained from bis-silylated precursors (R'O)(3)-R-Si(OR')(3) (R' = Me, Et and R = (-CH(2))(n)-, n = 1, 2, 6, 10, 12;--CH=CH-; (-CH(2))(3)NH(CH(2))(3)-; 1, 1'-ferrocenyl; (CH(2))(n)-Ph-(CH(2))(n)- with Ph = 1,4-phenylene and n = 0, 1, 2; Ph = 1,3,5-phenyl and n = 0) were analysed. The results were highly dependent on the nature of the organic group. When the organic group was small or 'rigid', the main peaks detected corresponded to SiOH and SiOR' residual groups. Fragment ions from the organic group were poorly detected in this case. When the organic group was larger and more 'flexible', characteristic mass fragment ions were detected at higher relative intensities, indicative of a different organization of the organic units in the solid. TOF-SIMS clearly showed the differences between the xerogels derived from mono- and bis-silylated organic precursors : the organic group is present at the surface of mono-silylated xerogels, whereas for bis-silylated ones, the organization is dependent on the length and the flexibility of the organic units. These TOF-SIMS results are in agreement with other features already reported. Copyright 1999 John Wiley & Sons, Ltd.

Characterization of the surface organization of nanostructured hybrid organic–inorganic materials by time‐of‐flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been used to analyse the surface composition of organic–inorganic hybrid solids obtained by a sol-gel process. Gels of type O1.5Si-R-SiO1.5, obtained from bis-silylated precursors (R′O)3-R-Si(OR′)3 (R′ = Me, Et and R = (-CH2)n-, n = 1, 2, 6, 10, 12;­-CH=CH-; (-CH2)3NH(CH2)3-; 1, 1′-ferrocenyl; (CH2)n-Ph-(CH2)n- with Ph = 1,4-phenylene and n = 0, 1, 2; Ph = 1,3,5-phenyl and n = 0) were analysed. The results were highly dependent on the nature of the organic group. When the organic group was small or ‘rigid’, the main peaks detected corresponded to SiOH and SiOR′ residual groups. Fragment ions from the organic group were poorly detected in this case. When the organic group was larger and more ‘flexible’, characteristic mass fragment ions were detected at higher relative intensities, indicative of a different organization of the organic units in the solid. TOF-SIMS clearly showed the differences between the xerogels derived from mono- and bis-silylated organic precursors : the organic group is present at the surface of mono-silylated xerogels, whereas for bis-silylated ones, the organization is dependent on the length and the flexibility of the organic units. These TOF-SIMS results are in agreement with other features already reported. Copyright © 1999 John Wiley & Sons, Ltd.