Gas Cluster Ion Beam Research Articles

Direct Mapping of Phospholipid Ferroptotic Death Signals in Cells and Tissues by Gas Cluster Ion Beam Secondary Ion Mass Spectrometry (GCIB‐SIMS)

AbstractPeroxidized phosphatidylethanolamine (PEox) species have been identified by liquid chromatography mass spectrometry (LC‐MS) as predictive biomarkers of ferroptosis, a new program of regulated cell death. However, the presence and subcellular distribution of PEox in specific cell types and tissues have not been directly detected by imaging protocols. By applying gas cluster ion beam secondary ion mass spectrometry (GCIB‐SIMS) imaging with a 70 keV (H2O)n+ (n>28 000) cluster ion beam, we were able to map PEox with 1.2 μm spatial resolution at the single cell/subcellular level in ferroptotic H9c2 cardiomyocytes and cortical/hippocampal neurons after traumatic brain injury. Application of this protocol affords visualization of physiologically relevant levels of very low abundance (20 pmol μmol−1 lipid) peroxidized lipids in subcellular compartments and their accumulation in disease conditions.

Bevel Structure Based XPS Analysis as a Non-Destructive Chemical Probe for Complex Interfacial Structures of Organic Semiconductors.

The bevel structure of organic multilayers produced by finely controlled Ar gas cluster ion beam sputtering preserves both the molecular distribution and chemical states. Nevertheless, there is still an important question of whether this method can be applicable to organic multilayer structures composed of complex or ambiguous interfaces used in real organic optoelectronic devices. Herein, various bevel structures are fabricated from different types of organic semiconductors using a solution-based deposition technique: complicatedly intermixed electron-donor and electron-acceptor bulk heterojunction structure, thin film structure with an internal donor-acceptor concentration gradient, and multi-layered structure with more than three layers. For these organic material combinations listed above, the bevel structure is fabricated with finely tuned Ar gas cluster ion beam sputtering. The location-dependent X-ray photoelectron spectroscopy (XPS) results obtained for each bevel structure exactly correspond to the XPS depth profiles. This result demonstrates that the bevel structure analysis is a powerful method to distinguish subtle differences in chemical component distributions and chemical states of organic semiconductors even with complex or ambiguous interfaces. Ultimately, due to its reliability as verified by this study, the proposed bevel structure analysis is expected to greatly expand other analytical techniques with a limited spatial or depth resolution.

The Interface Characterization of 2-Mercapto-1-methylimidazole Corrosion Inhibitor on Brass

This work presents a detailed surface analytical study and surface characterization, with an emphasis on the X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses of 2‑mercapto‑1‑methylimidazole (MMI) as a corrosion inhibitor for brass. First, the electrochemical measurements demonstrated a corrosion inhibition effect of MMI in a 3 wt.% NaCl solution. Next, the formation of the MMI surface layer and its properties after 1 month of immersion was analyzed with attenuated total reflectance–Fourier-transform infrared spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, and contact angle analysis. Moreover, to gradually remove the organic surface layer, a gas cluster ion beam (GCIB) sputtering source at different accelerated voltages and cluster sizes was employed. After each sputtering cycle, a high-resolution XPS analysis was performed. Moreover, an angle‑resolved XPS analysis was carried out for the MMI-treated brass sample to analyze the heterogeneous layered structure (the interface of the MMI organic/inorganic brass substrate). The interface properties were also investigated in detail using ToF-SIMS for spectra measurements and 2D imaging. Special attention was devoted to the possible spectral interferences for MMI‑related species. The thermal stability of different MMI-related species using molecular-specific signals without possible spectral interferences was determined by performing a cooling/heating experiment associated with ToF-SIMS measurements. It was shown that these species desorbed from the brass surface in the temperature range of 310–370 °C.

The influence of the amino group in 3-amino-1,2,4-triazole corrosion inhibitor on the interface properties for brass studied by ToF-SIMS.

RationaleThe detailed surface analysis of corrosion inhibitor surface layers by the application of 1,2,4‐triazole (TRI) and 3‐amino‐1,2,4‐triazole (3‐AT) compounds adsorbed from a 3 wt. % NaCl solution on the brass surface was performed by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The results obtained were additionally supported by X‐ray photoelectron spectroscopy (XPS) measurements.MethodsThe description of the corrosion inhibitor surface layers was elaborated by using ToF‐SIMS and molecular‐specific signals. Characteristic molecular‐specific signals were used to perform 2D ToF‐SIMS imaging and cooling/heating experiment associated with ToF‐SIMS measurements. A detailed surface analysis using high‐resolution angle‐resolved XPS and gas cluster ion beam sputtering in combination with XPS measurements was also carried out.ResultsOrganometallic complexes were formed after the corrosion process of brass with the release of Cu and Zn ions that subsequently connect with TRI or 3‐AT. Using ToF‐SIMS, possible spectral interferences of the organometallic species were considered due to the presence of different organometallic compounds composed of the two main Cu and Zn isotopes, that is, 63Cu and 65Cu and 64Zn and 66Zn. Using the molecular‐specific signals, 2D imaging was performed, which showed a different distribution of different species on the brass surface. In addition, a ToF‐SIMS experiment on thermal stability showed that most of the TRI‐ and 3‐AT‐related species desorb from the brass surface at 460 °C and 405 °C, respectively.ConclusionsToF‐SIMS analysis confirmed the formation of Cu/Zn‐ or Cu2‐inhibitor organometallic complexes, whereas the formation of Zn2‐inhibitor organometallic complexes on the brass surface was not confirmed. ToF‐SIMS imaging showed complete coverage of the brass surface with different Cu/Zn‐ or Cu2‐inhibitor organometallic complexes. The high thermal stability of the corrosion inhibitor surface layers was confirmed by ToF‐SIMS.

Method for Molecular Layer Deposition Using Gas Cluster Ion Beam Sputtering with Example Application In Situ Matrix-Enhanced Secondary Ion Mass Spectrometry.

We introduce a technique for the directed transfer of molecules from an adjacent reservoir onto a sample surface inside the vacuum chamber of a ToF-SIMS instrument using gas cluster ion beam (GCIB) sputtering. An example application for in situ matrix-enhanced secondary ion mass spectrometry (ME SIMS) is provided. This protocol has attractive features since most modern SIMS instruments are equipped with a GCIB gun. No solvents are required that would delocalize analytes at the surface, and the transfer of matrix molecules can be interlaced with SIMS depth profiling and 3D imaging sputtering and analysis cycles, which is not possible with conventional ME SIMS strategies. The amount of molecular deposition can be finely tuned, which is important for such a surface sensitive technique as SIMS. To demonstrate the concept, we used 2,5-DHB as a matrix for the enhancement of three drug molecules embedded in a tissue homogenate. By automatic operation of sputter deposition and erosion (cleanup) cycles, depth profiling could be achieved with ME SIMS with good repeatability (<4% RSD). Furthermore, we explored several different matrix compounds, including α-CHCA and aqueous solutions of Brønsted acids (formic acid) and 3-nitrobenzonitrile, a volatile compound known to spontaneously produce ions. The latter two matrix compounds were applied at cryogenic measurement conditions, which extend the range of matrices applicable for ME SIMS. Enhancement ratios range from 2 to 13, depending on the analytes and matrix. The method works in principle, but enhancement ratios for the drug molecules are rather limited at this point. Further study and optimization is needed, and the technique introduced here provides a tool to perform systematic studies of matrix compounds and experimental conditions for their potential for signal enhancement in ME SIMS.

Dark current issues for high gradient C-band medical linac

Simulations of dark current emission for C-band linear accelerating structure were performed taking into account the electric field distributions inside the cavities and the field enhancement factor. Matching calculated dark current energy spectra with the experimentally measured ones made it possible to understand the nature of the dark current and to reveal the areas of the accelerating structure requiring improved surface treatment. Microscopic investigation of the copper accelerating cell surface treated using different techniques showed that gas cluster ion beam irradiation results in the best surface smoothness. Furthermore, it removes the surface insulating layers and prevents from subsequent oxidizing. Both effects can significantly reduce the dark current emission.

Surface analysis by gas cluster ion beam XPS and ToF-SIMS tandem MS of 2-mercaptobenzoxazole corrosion inhibitor for brass

This work presents the first study on 2-mercaprobenzoxazole (MBOH) as a corrosion inhibitor for brass in chloride solution. The corrosion inhibition effect was conclusively demonstrated. A detailed surface analysis using gas cluster ion beam (GCIB) and monoatomic Ar+ sputter beams in combination with X-ray photoelectron spectroscopy (XPS) measurements was performed. Furthermore, time-of-flight secondary ion mass spectrometry (ToF-SIMS) tandem MS (MS/MS) was used for large-area imaging, to proof the MBOH-specific peak, and to show the 3D distribution of MBOH, Cu, Zn, and Cl– species at the organics/brass interface by GCIB and C60+ sputtering in combination with ToF-SIMS analysis.

Effect of ion dose ratio on multilevel energy smoothing model of gas cluster

In this study, two kinds of gas cluster ion beam energy modes with different ion dose ratios are proposed to improve the traumatic surface of n-Si (100) single crystal. In mode1, low-dose high-energy clusters and high-dose low-energy clusters are used, while in mode2, high-dose high-energy clusters and low-dose low-energy clusters are used. The results show that the flattening effect of mode 1 is better than that of mode 2, and the root mean square roughness of mode 1 and mode 2 are 0.62 nm and 1.02 nm, respectively. This is because in multi-level energy mode 2, high-dose high-energy clusters are used to bombard the target surface in the early stage, so that more ion damages will be left after high-energy cluster bombardment. In the later stage, low-dose low-energy clusters can only remove part of the ion damages, and the repair strength is not strong enough. In multi-level energy mode1, we first use low-dose high-energy clusters to bombard the surface of the target, so that the high-energy clusters can quickly remove the shape objects with high protrusion on the sample surface, and in the low-dose mode, it will not leave too many ion damages, which is conducive to the later repair. In the first stage of multi-level energy mode, high-dose low-energy clusters are used to bombard the target surface, which can not only reduce the ion loss, but also increase the time for low-energy clusters to repair ion damages, thereby yielding the optimal flattening effect. In order to verify the relationship among the damage removal, ion damage degree and cluster energy, a single energy cluster bombardment experiment with mechanical damage is carried out before the multi-level energy mode modification is studied. The results show that when the cluster ions are accelerated at 15 kV high voltage, the scratch removal efficiency is highest, and the surface scratch is very shallow, but the decease of roughness is not obvious; when the cluster ions are accelerated at 8 kV and 5 kV, the sample surface becomes fine and the remaining ion damages are least. At the same time, a comparison of the target bombarded by the multi-level energy mode 1 clusters with that by the single energy clusters shows that the multi-level energy mode can obtain a smoother target surface than the single 15 keV high-energy cluster treatment; the multi-level energy mode can better remove scratches and other wounds than the single 5 keV low-energy cluster treatment. Multistage energy mode 1 integrates the advantages of high and low energy clusters, thereby achieving the best flattening effect.

Surface Reactions Induced by Gas Cluster Ion Beams and Application for Atomic Layer Etching

Surface Reactions Induced by Gas Cluster Ion Beams and Application for Atomic Layer Etching

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

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

(Invited) Reactions on Metal Surface and Diketone Induced By Gas Cluster Ions during Atomic Layer Etching

Gas cluster ion beams (GCIB), which consists of several thousands of gaseous atoms or molecules, have been used as novel low-energy ion beams for surface processing and analysis. Since thousands of low-energy (several eV) atoms bombard a surface at the same time and the same position, the bombarded area experiences transient high-temperature and high-pressure conditions, which enhance sputtering of atoms or enhance surface reactions. In recent years, we have been investigating to apply GCIB as energetic ions for atomic layer etching. We have reported ALE of transition metals (Cu and Ni) with GCIB irradiations and diketone (acetylacetone and hexafluoroacetone). We separated each etching step as following; (1) adsorption of diketone molecules on metal oxide, (2) evacuation of residual vapor, (3) irradiation of oxygen GCIB to remove metal oxide. By using 5 keV oxygen GCIB (~ 2eV/molecules), thin layer of nickel oxide with adsorbed acetylacetone is removed. There is no physical sputtering at this energy region, which realizes self-limiting ALE process. From in-situ XPS study, Ni oxide with adsorbed diketone molecules can be removed by Ar-GCIB irradiation. It means that other oxidation method can be used to form metal oxide, and Ar-GCIB can be used for the removal steps. In this talk, we will report surface reactions between metals and diketone induced by gas cluster ion irradiations, and etching characteristics of various metals using GCIB irradiation and diketone.

Surface Analysis of 4-Methyl-2-Phenylimidazole Corrosion Inhibitor on Brass

This work presents the first corrosion analysis of 4-methyl-2-phenylimidazole (MePhI) corrosion inhibitor for brass immersed in 3 wt.% NaCl solution, wherein MePhI was shown to be highly effective. Moreover, the structure of the surface layer, the formation of an organo-metallic complex, the spatial distribution of MePhI, and the thermal stability of the MePhI surface layer were described in detail using time-of-flight secondary ion mass spectrometry analysis and X-ray photoelectron spectroscopy. Furthermore, a gas cluster ion beam source using different sizes and accelerating energies of the clusters was also employed to slowly sputter the organic surface layer associated with the surface layer analysis.

Improvement of the lubrication properties of grease with Mn3O4/graphene (Mn3O4#G) nanocomposite additive

Although grease can effectively lubricate machines, lubrication failure may occur under high speed and heavy load conditions. In this study, Mn3O4/graphene nanocomposites (Mn3O4#G) were synthetized using a hydrothermal method as lubricant additives. The lubrication properties of compound grease with Mn3O4#G nanocomposite additive under heavy contact loads of 600–900 N (3.95–4.59 GPa) were investigated. First, the nanocomposites were dispersed into L-XBCEA 0 lithium grease via successive electromagnetic stirring, ultrasound vibration, and three-roll milling. Compound grease with additives of commercial graphene (Com#G) was also investigated for comparison. Tribological test results revealed that the trace amounts of Mn3O4#G (as low as 0.02 wt%) could reduce the coefficient of friction (COF) of grease significantly. When the concentration of Mn3O4#G was 0.1 wt%, the COF and wear depth were 43.5% and 86.1%, lower than those of pure graphene, respectively. In addition, under the effect of friction, the microstructure of graphene in Mn3O4#G nanocomposites tends to be ordered and normalized. Furthermore, most of the Mn3O4 transformed into Mn2O3 owing to the high temperature generated from friction. Using the Ar gas cluster ion beam sputtering method, the thickness of the tribofilm was estimated to be 25–34 nm. Finally, the improvement of the lubrication properties was attributed to the synergistic effect of the adsorbed tribofilm, i.e., the graphene island effect and the filling effect of Mn3O4#G.

Protein identification by 3D OrbiSIMS to facilitate in situ imaging and depth profiling

Label-free protein characterization at surfaces is commonly achieved using digestion and/or matrix application prior to mass spectrometry. We report the assignment of undigested proteins at surfaces in situ using secondary ion mass spectrometry (SIMS). Ballistic fragmentation of proteins induced by a gas cluster ion beam (GCIB) leads to peptide cleavage producing fragments for subsequent OrbitrapTM analysis. In this work we annotate 16 example proteins (up to 272 kDa) by de novo peptide sequencing and illustrate the advantages of this approach by characterizing a protein monolayer biochip and the depth distribution of proteins in human skin.

Double-step gas cluster ion beam smoothing

In this study we use the double step gas cluster ion beam treatment to improve smoothing process of mechanically polished 4H-SiC (1000) wafers and compare it with conventional single-step smoothing. The first step is a higher energy treatment with 15 keV Ar cluster ions, and the second step is a lower 5 keV treatment. Single-step treatments are performed at 15 and 5 keV. It is shown that single-step 15 keV smoothing as compared with lower 5 keV one is very effective for removing the initial surface morphological feature (scratches), however, cluster ions impacting on the surface can create larger craters, resulting in roughness &lt;i&gt;R&lt;/i&gt;&lt;i&gt;&lt;sub&gt;q&lt;/sub&gt;&lt;/i&gt; of 1.05 nm. Whereas, 5 keV treatment at a selected fluence cannot remove initial scratches, which requires using higher fluences, i.e. such smoothing becomes time consuming. On the other hand, crater morphology with such a treatment is less developed, hence, the roughness slightly decreases to 0.9 nm. Using the double-step treatment, one can obtain the surface with lower &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;&lt;i&gt;q&lt;/i&gt;&lt;/sub&gt; roughness of 0.78 nm as compared with single-step treatment, at the same total cluster ion fluence. Therefore, the double-step treatment combines the advantages of the effective smoothing of scratches at high energy and smaller crater morphology at low energy. To evaluate the contribution of the cluster morphology introduced by the accelerated clusters into the total roughness, the cluster ion beam treatment of an atomically smooth 4H-SiC (1000) surface is also carried out. It is shown that the crater diameter increases in a range of 15–30 nm with the cluster energy increasing. More detailed analysis of the smoothing process is carried out by using two-dimensional isotropic PSD function. It is shown that the cluster treatment of mechanically polished 4H-SiC wafers effectively reduces the roughness in a wavelength range of 0.05–0.20 μm and the efficiency of smoothing is higher at higher cluster energy. In a range of 0.02–0.05 μm, a roughening effect is observed, which is due to the formation of craters. This roughening effect can be effectively reduced by the subsequent lower energy step treatment, which can be shown by the PSD function analysis of the smooth SiC surface treated initially by cluster ion beam.

Surface analysis and interface properties of 2-aminobenzimidazole corrosion inhibitor for brass in chloride solution.

This work presents a corrosion study of 2-aminobenzimidazole (ABI) as a corrosion inhibitor for brass in chloride solution. Electrochemical, field emission scanning electron microscopy, atomic force microscopy, and contact angle measurements showed that ABI mitigates brass corrosion after short-, medium-, and long-term immersion periods. Next, a detailed surface analysis of the ABI adsorbed on the brass surface was performed using attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) techniques. XPS imaging was performed in association with principal component analysis to determine the different phases on the surface. In order to describe the in-depth composition of the ABI surface, an angle-resolved XPS analysis was performed. This analysis was further supported by gas cluster ion beam sputtering to gradually remove the ABI surface layer, and XPS analysis was performed after each sputtering cycle. Finally, TOF-SIMS analyses showed the formation of Cu/Cu2-ABI and Zn-ABI compounds, the 2D distribution of ABI-related compounds, and their thermal stability on the brass surface. Graphical abstract.

Development and analysis of frits for enamelling AA2024, AA6082 and AA7075 aluminium alloys

AbstractThis study reports the development of frits with different composition, time, and firing temperature for mitigating the corrosion of AA2024, AA6082, and AA7075 aluminium alloys in chloride‐containing solutions. The melting points of the frits were determined using a heating microscope, while the thermal expansion was measured using dilatometry. Several frits were prepared, of which seven were coated on AA2024, AA6082 and AA7075 aluminium alloys. The corrosion resistance of the coated samples was tested in 5 wt% NaCl solution at 25°C using potentiodynamic curve measurements. The corrosion resistance of the coated samples increased compared with the respective uncoated aluminium alloys. The composition and in‐depth homogeneity of the best‐performing coated samples were confirmed using a gas cluster ion beam sputtering source associated with X‐ray photoelectron spectroscopy analysis. Furthermore, O2+ sputtering was performed in association with time‐of‐flight secondary ion mass spectrometry to describe the three‐dimensional composition of the frits.

Internal Diesel Injector Deposit Chemical Speciation and Quantification Using 3D OrbiSIMS and XPS Depth Profiling

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The impact of internal diesel injector deposits (IDIDs) on engine performance, efficiency and emissions remains a major concern in the automotive industry. This has been compounded in recent years by fuel injection equipment developments and changes to diesel fuel towards ultra-low sulfur diesel (ULSD) and biodiesel as well as the introduction of new fuels such as hydrotreated vegetable oil (HVO). Prevention and mitigation of such deposit formation requires an understanding of the formation process, which demands a chemical explanation. The chemistry of these deposits therefore remains a key research interest to the industry using the latest analytical methodologies to inform and build further on previous investigations. In this work, 3D OrbiSIMS analysis using a time of flight-secondary ion mass spectrometer (ToF-SIMS) with hybrid Orbitrap&lt;sup&gt;TM&lt;/sup&gt; functionality has been employed for chemical speciation and depth profiling of IDIDs in-situ on two injector needle samples from field failures in China and Eastern USA. The instrument’s soft gas cluster ion beam (GCIB) and high mass resolution enables unequivocal identification of chemistries from several classes of compounds. Here, chemistries identified include alkylbenzene sulfonates, zinc oxides, sodium and calcium salts, carboxylic acids, carbonaceous/polyaromatic hydrocarbons and metal substrate related material. With depth profiling, the distributions of these materials are traced throughout the deposit thickness. Given the semi-quantitative nature of SIMS data, X-ray photoelectron spectroscopy (XPS) depth profiling using an argon GCIB has also been employed to provide parallel data of atomic concentration through the deposit thickness. This data is complementary to SIMS as it places the chemical information in a quantitative context, most notably showing that despite the extreme intensities of salt material in the SIMS data, carbon is the main element throughout both IDIDs. Together the techniques show in general the more functionalized chemistries are at the deposit surface, with underlying salt layers and innermost layers of more amorphous organic material. These techniques represent a new method of comprehensive IDID characterization that affords diagnostic chemical information alongside elemental quantification, thus complementing previous studies.&lt;/div&gt;&lt;/div&gt;

Advanced surface analysis using GCIB-C60++-tandem-ToF-SIMS and GCIB-XPS of 2-mercaptobenzimidazole corrosion inhibitor on brass

A gas cluster ion beam (GCIB) sputtering source in association with high-resolution X-ray photoelectron spectroscopy measurements were employed to slowly sputter and analyze a 2-mercaptobenzimidazole (MBIH) corrosion inhibitor surface layer on brass substrate after immersion in chloride solution. Furthermore, ToF-SIMS measurements and imaging were performed to further describe the structure of this surface layer. In addition, the powerful nature of the tandem ToF-SIMS (MS/MS) technique was demonstrated to detect and confirm the organometallic complexes that formed among the brass corrosion products and MBIH. Also, the issue of spectral interferences was considered for the organometallic complexes of 63Cu, 65Cu, 64Zn, and 66Zn in combination with MBIH. Large-area ToF-SIMS imaging (4.8 by 3.2 mm) in positive and negative polarities was performed to show the 2D distribution of the MBIH on the brass surface. Finally, 3D ToF-SIMS imaging using GCIB and C60++ sputtering sources showed the depth distribution of different species at the MBIH/brass interface. This type of analytics is currently state-of-the-art in the surface analysis of corrosion inhibitors.

Ion yield enhancement at the organic/inorganic interface in SIMS analysis using Ar-GCIB

Argon gas cluster ion beams (Ar-GCIBs) provide new opportunities for molecular depth profiling and imaging of organic materials and biological samples, thanks to recent technological developments that have led to the construction of new SIMS spectrometers where the traditional issues related to their low lateral resolution along with poor mass resolution and mass accuracy are overcome. The present fundamental contribution on SIMS molecular depth profiling investigates the variations of the secondary ion signals observed at the organic–inorganic hybrid interface when using Ar-GCIB as the analytical beam. With this in mind, depth profiling experiments were performed with a ToF-SIMS spectrometer using different analysis beams: 30-keV Bi5+ versus 10-keV Arn+ with a cluster size (n) of 800, 1500, 3000 and 5000 atoms, respectively. A 10-keV Ar3000+ beam was used for sputtering in all the experiments. Irganox 1010 and model polymers such as polystyrene (PS) and poly (methyl methacrylate) (PMMA) oligomers were chosen. Silicon wafer and a polymer-based substrates were employed to test materials with different stiffness, which is directly related to their Young’s moduli, an important parameter in this study. Ar-GCIB depth profiles systematically show ion signal enhancement of the characteristic fragments of PS and Irganox 1010 when approaching the interface with the silicon substrate, that can reach up to 60% for [M1010-H]− in Irganox films deposited onto silicon wafers. This enhancement increases with increasing n in both ion polarities. These results point out some ionization effects on the observed signal enhancement at the interface. The experimental observations will be explained on the basis of the physics of the impact of large argon clusters on different target materials and the energy confinement of the ion projectile in the organic overlayers. Finally, the thickness of organic films on rigid substrates in the nanoscale appears to be a crucial parameter to dramatically improve the sensitivity to molecular fragments when using large Ar cluster ions as analysis beams.