Time-of-flight Secondary Ion Mass Spectrometer Research Articles

Effects of AlOx Sub‐Oxide Layer on Conductance Training of Passive Memristor for Neuromorphic Computing

AbstractMemristors are recognized as crucial devices for the hardware implementation of neuromorphic computing. The conductance training process of memristors has a direct impact on the performance of neuromorphic computing. However, memristor breakdown and conductance decay still hinder the precise training process of neural networks based on passive memristor. Here, AlOx/LiNbO3 (LN) memristors are designed by inserting a AlOx sub‐oxide layer between the single‐crystalline LN thin film with oxygen vacancies (OVs) and Pt layer. Under the same training conditions, lower conductance and self‐compliance current effects are observed in AlOx/LN memristor. Slight spontaneous decay of conductance is achieved after the removal of the external stimulation. To explore the effects of AlOx sub‐oxide layer on the prevention of device breakdown and suppression of conductance decay, the memristive mechanism of devices with and without AlOx layer is revealed via time‐of‐flight secondary ion mass spectrometer (ToF‐SIMS). It is reasonable to believe that the AlOx inserting layer in memristors can serve as a self‐compliance current layer to inhibit device breakdown and provide the OVs reservoir to suppress conductance decay. These results offer new possibilities and theoretical grounds for achieving more reliable and precise conductance training of passive memristors.

Verification of permeability for ionic liquid into biological specimens by using a mass spectrometer.

The pretreatment method with ionic liquids (ILs) is convenient for scanning electron microscope (SEM) observation of biological specimens. It needs neither fixation nor vacuum vapor deposition of metals to prevent fracture, deformation and charge-up. Although it was pointed out that the reason why the specimens are not fractured or deformed under the vacuum without fixation is the penetration of the ILs into cells and replacement with the intercellular water of the specimen, the experimental results were not yet self-consistent. In this study, in order to verify this hypothesis, we investigated whether the components of 1-ethyl-3-methylimidazolium methylphosphonate ([EMIM][MePO3]) are detectable by using a time-of-flight secondary ion mass spectrometer (TOF-SIMS) and liquid chromatography. It was found that the components of [EMIM][MePO3] could be detected from inside of the biological specimens. Moreover, it was verified that there is no fracture and deformation of the specimen, whose residual concentration of the IL on the surface would be less than the limit of detection by TOF-SIMS. Therefore, these experimental results explicitly show that penetration of [EMIM][MePO3] into the specimen and subsequent replacement with the intercellular water inside the body is the reason for preventing fracture and deformation of the specimen under the vacuum.

Observation of hydrogen trap and hydrogen embrittlement of 430 ferritic stainless steel

The hydrogen distribution and content in AISI430 ferritic stainless steel (FSS) were revisited via time-of-flight secondary ion mass spectrometer (TOF-SIMS) and thermal desorption spectroscopy (TDS) in this paper. As irreversible hydrogen traps, carbides have stronger hydrogen trapping capabilities and the activation energy of hydrogen desorption (Eb) is 44.37 KJ/mol, which is higher than the lattice/grain boundaries (GB) (18.18 KJ/mol). Hydrogen changed the stress level state at the crack tip and increased the crack growth rate. High hydrogen concentration promoted the hydrogen-enhanced decohesion (HEDE) mechanism, causing the microcracks to preferentially nucleate at the interface between the carbide and the matrix, with the fracture mode changed from micro-void coalescence (MVC) fracture to quasi-cleavage (QC) fracture.

Probing Surface Information of Alloy by Time of Flight-Secondary Ion Mass Spectrometer

In recent years, time of flight-secondary ion mass spectrometer (ToF-SIMS) has been widely employed to acquire surface information of materials. Here, we investigated the alloy surface by combining the mass spectra and 2D mapping images of ToF-SIMS. We found by surprise that these two results seem to be inconsistent with each other. Therefore, other surface characteristic tools such as SEM-EDS were further used to provide additional supports. The results indicated that such differences may originate from the variance of secondary ion yields, which might be affected by crystal orientation.

Component distribution of nano-carbon materials assisted by Time of Flight-Secondary Ion Mass Spectrometer

Currently, there exist various materials surface analysis and characterization techniques, but it is difficult to measure their component distribution, in particular from a three-dimensional prospect. In this paper, the component distribution of nano-carbon materials in 2D and 3D views were both characterized via Time of Flight-Secondary Ion Mass Spectrometer (TOF-SIMS). The results indicate that TOF-SIMS could provide comprehensive information about component distribution, which is expected to be developed as an advanced technology in material analysis and characterization to the research community.

Acquisition of artifact free alkali metal distributions in SiO2 by ToF‐SIMS Cs+ depth profiling at low temperatures

Artifact‐free depth profiles of alkali ions in SiO2 were obtained using a time‐of‐flight secondary ion mass spectrometer (ToF‐SIMS) equipped with a Cs+ beam as sputter gun. Samples were set to low temperature (~−100°C) using a heating/cooling sample holder. The effects of temperature on the depth profiles was determined with multiple measurements at different temperatures. To validate the described method, obtained depth profiles of alkali metal implanted SiO2 samples were compared with simulated depth profiles. Evidence for artifact‐free depth profiles is given for potassium, sodium, and lithium, three prominent examples of fast diffusing ions in various materials. This described approach enables more laboratories to acquire depth profiles of alkali metals in non‐conducting samples without time‐consuming sample preparation. It offers artifact‐free depth profiling of alkali metals using a classic ToF‐SIMS without advanced extensions, which are not available in many laboratories.

Observation of hydrogen diffusion channel and hydrogen trap in 304 austenitic stainless steel

Hydrogen embrittlement (HE) involves hydrogen-defect interactions at multiple-length scales. However, the challenge of measuring the precise location of hydrogen atoms limits our understanding. We used time of flight-secondary ion mass spectrometer (TOF-SIMS) to observe hydrogen localization in 304 austenitic stainless steel. A large amount of hydrogen observed at grain boundary in cold-rolled steel contains strain-induced α′-martensite provides direct evidence that α′-martensite act as hydrogen diffusion channel and grain boundaries act as trapping sites, which achieves a mechanistic understanding of hydrogen materials interactions and facilitates the development of hydrogen-resistant steels.

Impurity diffusion behavior study of electroplated copper films annealed by linear shaping laser mobile scanning system

Impurities due to additives in electroplated copper interconnects diffuse during grain growth. High-resolution electron backscatter diffraction and TOF-SIMS (Time-of-flight secondary ion mass spectrometer) results reveal that the electroplated copper films after laser annealing by linear shaping laser mobile scanning system (LALS) have higher recrystallization fraction and less impurity content than traditional thermal annealing. Impurity diffusion behavior and grain boundary migration are inseparable. The effect of LALS on the impurity diffusion of electroplated Cu films is the result of the introduced local temperature gradient, which works collaboratively on the thermodynamics and kinetics of grain boundary migration. And the amount of impurity diffusion is related to the proportion of different species of impurities. The findings are meaningful for the metallization of electroplated copper interconnects.

Deposition of Intact and Active Proteins In Vacuo Using Large Argon Cluster Ion Beams.

Providing inert materials with a biochemical function, for example using proteins, is a cornerstone technology underlying many applications. However, the controlled construction of protein thin films remains a major challenge. Here, an innovative solvent-free approach for protein deposition is reported, using lysozyme as a model. By diverting a time-of-flight secondary ion mass spectrometer (ToF-SIMS) from its standard analytical function, large argon clusters were used to achieve protein transfer. A target consisting of a pool of proteins was bombarded with 10 keV Ar5000+ ions, and the ejected proteins were collected on a silicon wafer. The ellipsoidal deposition pattern was evidenced by ToF-SIMS analysis, while SDS-PAGE electrophoresis confirmed the presence of intact lysozyme on the collector. Finally, enzymatic activity assays demonstrated the preservation of the three-dimensional structure of the transferred proteins. These results pave the way to well-controlled protein deposition using ion beams and to the investigation of more complex multilayer architectures.

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

<div class="section abstract"><div class="htmlview paragraph">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<sup>TM</sup> 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.</div></div>

Effect of the support composition on catalytic and physicochemical properties of Ni catalysts in oxy-steam reforming of methane

This work deals with Ni catalysts supported on both mono and binary oxide prepared by a conventional wet impregnation method. The catalytic properties of the material were investigated in oxy-steam reforming of methane (OSRM) process. The physicochemical properties of the catalysts were extensively studied using techniques such as Temperature Programmed Reduction (TPR-H2), Temperature Programmed Desorption of Ammonia (TPD-NH3), Brunauer Emmett Teller Method (BET), X-ray Diffraction studies (XRD), Thermal Analysis coupled with Mass Spectrometry (TG-DTA-MS), Time of Flight Secondary Ion Mass Spectrometer (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscope with EDX detector (SEM-EDX). The catalytic activity results showed that the Ni/CeO2∙La2O3 (2:1) catalyst exhibited superior activity and high selectivity towards hydrogen formation in the studied process due to the high content of Ni species present on the catalyst surface. The low activity of the Ni catalysts supported on La2O3 or binary oxide with high content of lanthanum oxide is related to the strong interaction of NiO with support.

Biodegradation, hemocompatibility and covalent bonding mechanism of electrografting polyethylacrylate coating on Mg alloy for cardiovascular stent

Organic coatings are the most widely employed approach for the promotion of corrosion resistance of magnesium (Mg) alloys. Unfortunately, traditional organic coatings are weakly bonded to Mg substrates due to physical adsorption. Herein, a polyethylacrylate (PEA) coating was fabricated on Mg-Zn-Y-Nd alloy via electro-grafting. The surface structure and chemical composition were characterized by means of scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscope (AFM) and Fourier transform infrared (FTIR) as well as time of flight-secondary ion mass spectrometer (ToF-SIMS). The results showed that the surface roughness of PEA coating was dominated by scan rate; while the coverage and integrity of PEA coating were mainly affected by the monomer concentration and sweep circles. ToF-SIMS results indicated that PEA coating was wholly covered on Mg alloy, and the presence of C2H3Mg− fragment confirmed the covalent bond between PEA coating and Mg alloy. In addition, DFT calculation results of the adsorption of EA molecules with Mg substrate agree well with the experimental phenomena and observation, suggesting that the electrons in 3 s orbit of Mg atoms and 2pz orbit of C1 atom participated in the formation of covalent bond between PEA coating and Mg substrate. Potentiodynamic polarization curves and immersion test demonstrated that the PEA coatings could effectively enhance the corrosion resistance of Mg alloy. The platelet adhesion results designated that platelets were barely visible on PEA coating, which implied that PEA coating could effectively prevent the thrombosis and coagulation of platelets. PEA coating might be a promising candidate coating of Mg alloy for cardiovascular stent.

Electrical properties of cometary dust particles derived from line shapes of TOF-SIMS spectra measured by the ROSETTA/COSIMA instrument

Between Aug. 2014 and Sept. 2016, while ESA’s cornerstone mission Rosetta was operating in the vicinity of the nucleus and in the coma of comet 67P/Churyumov-Gerasimenko, the COSIMA instrument collected a large number of dust particles with diameters up to a millimeter. Positive or negative ions were detected by a time-of-flight secondary ion mass spectrometer (TOF-SIMS) and the composition of selected particles was deduced. Many of the negative ion mass spectra show, besides mass peaks at the correct position, an additional, extended contribution at the lower mass side caused by partial charging of the dust. This effect, usually avoided in SIMS applications, can in our case be used to obtain information on the electrical properties of the collected cometary dust particles, such as the specific resistivity (ρr>1.2⋅1010Ωm) and the real part of the relative electrical permittivity (εr<1.2). From these values a lower limit for the porosity is derived (P>0.8).

Impact of Processing Conditions on Oxygen Vacancies in Ga-Doped Li7La3Zr2O12 Solid Electrolyte Using Tof-SIMS

Currently a vast amount of research into fast lithium ion conductors is taking place for application into solid electrolytes. The most attractive compositions being from the garnet family with the chemical composition of Li7La3Zr2O12 [1]. LLZO has high lithium ion mobility at room temperature, a large electrochemical window which allows high voltage cathodes to be employed and good stability with lithium metal anodes. Typically, LLZO is doped at the lithium position with donor cations these include Al3+and Ga3+ which provide stability of the cubic crystal phase thus allowing Li+ mobility in three dimensions. The mobility for Ga-LLZO has been reported to be above 10-3 S.cm-1 [2], [3] this is the composition that will be mainly focused on in the poster. Preliminary investigations have shown that due to lithium loss during high processing temperatures oxygen vacancies are formed because of the charge compensation mechanism[4]. The quantification of oxygen vacancies as an affect of the processing conditions and it effect on the conductivity of oxygen and lithium ions have been investigated in this work using electrochemical impedance spectroscopy and cell cycling. The affect of different densification atmospheres (Ar, Vac, and O2) on oxygen vacancies are measured using 18O isotopic labelling coupled with the Time of Flight Secondary Ion Mass Spectrometer (ToF-SIMS) to assess which results in a higher degree of oxygen defects. This work will be correlated with lithium defect chemistry and mobility to understand the lithium critical current density for dendrite growth which are detrimental to battery life.

Characterization of electrodes modified with nanocomposites of cobalt tetraaminophenoxyphthalocyanine, reduced graphene and multi-walled carbon nanotubes

Glassy carbon electrodes or plates were modified with nanocomposites consisting of cobalt tetraaminophenoxyphthalocyanine (CoTAPhPc), reduced graphene oxide nanosheets (rGONs) and multi-walled carbon nanotubes (MWCNTs). The modified electrodes were characterized using cyclic voltammetry, scanning electrochemical microscopy (SECM) and time-of-flight-secondary ion mass spectrometer (TOF-SIMS). The electrocatalytic activity of the modified electrode was tested for detection of L-cysteine. The presence of CoTAPhPc on sequential layers of MWCNT and rGONs resulted in improved detection currents compared to CoTAPhPc alone or when MWCNT/rGONs are mixed in CoTAPhPc–MWCNT/rGONs (mix)–glassy carbon electrode (GCE). CoTAPhPc–MWCNT–GCE (without rGONS) showed higher sensitivity toward l-cysteine as compared to the probes incorporating rGONs with a catalytic rate constant of 4.62 × 104 M−1s−1 and a detection limit of 30 nM. The presence of rGONs improved the stability of the electrode.

Self-Annealing Behavior of Electroplated Cu in the Blind-Hole Structure

Blind-hole (BH) metallization via electrolytic Cu fillings has become a critical technology for fabrication of high-density-interconnection (HDI) printed circuit boards in electronic industry because this technology provides excellent thermal and electrical conductivity and efficient utilization of space. The morphology and crystallographic orientation/texture of the Cu fillings governs the electrical, thermal, and mechanical properties of the interconnections, affecting the overall reliability of an electronic device. Although numerous publications concerning the self-annealing behavior (generally termed room-temperature recrystallization) of electroplated Cu, there is still limited information regarding such a time-dependent phenomenon in the BH structure. As the distributions of organic additives and current density in a BH structure is very different from on the flat substrate and is an important factor of Cu self-annealing, it is therefore of fundamental interest and importance to investigate the BH Cu microstructure transition in the self-annealing procedure. In this study, we probed into the crystallographic and resistance transitions of the Cu platings in a BH structure via an ohm meter and a field-emission scanning electron microscope (FE-SEM) in combination with electron backscatter diffraction (EBSD) analysis system. Additionally, the distribution of organic additives in a BH structure was characterized using a time of flight secondary ion mass spectrometer (TOF-SIMS). The knowledge advances our understanding of the evolution of the BH Cu filling physical/chemical properties during self-annealing. Figure 1

Effect of Brightener Concentration on Recrystallization Process of Electroplated Cu

It is well-known that self-annealing of as-electroplated Cu would cause remarkable microstructure transition in few hours, inducing grain growth accompanied by elimination of grain boundaries and crystallographic defects that determine the physical/chemical characteristics (e.g., resistivity, and hardness) of the Cu film. Organic additives (e.g., brightener, suppressor, and leveler) and current density are two important factors of Cu self-annealing. The brightener is an indispensable organic additive for the superfilling of Cu electroplating in blind-/through-hole structure. Hence, the focus of this study is to probe into the effect of brightener concentration (C b) on the self-annealing behavior of electroplated Cu. The crystallographic evolution of electroplated Cu, including grain size distribution, crystallographic orientation, grain boundaries, and residual strain, were investigated by means of in-situ X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). Additionally, the impurity distribution on the Cu film (e.g., C, O, S, and Cl) was investigated by a time of flight secondary ion mass spectrometer (TOF-SIMS). The research results indicated that the brightener concentration is a very important factor of Cu microstructure evolution and impurity distribution. The information advances our own knowledge of electrochemical metal recrystallization. Figure 1

Loss of Phosphate Determines the Versatility of a Spider Orb-web Glue Ball

Spiders capture their prey by weaving an "invisible" orb-web that has both adhesive and fixed properties. Different types of silk in the orb-web have different functions, wherein the key to capturing a prey is the ball-like glue (glue ball), which coats the silk strands. This glue ball has highly versatile properties, but the mechanisms leading to its versatility remain unclear. The salts found in the web have been previously suggested to play an important role in terms of viscosity, not water. However, the distribution of salt and water in the glue ball has not yet been directly observed. Here, we mapped the salts in different states using a homemade time-of-flight secondary ion mass spectrometer (TOF-SIMS) with a high lateral resolution. To our surprise, the glue ball was found to contain little water. The functional transformation of the glue ball from a viscous glycoprotein (capturing prey) to a hardened protein (retaining prey) relies solely on the stimulation of mechanical forces. The phosphate is a key factor for its versatility.

Influence of additives on electroplated copper films and their solder joints

An organosulfide, 3‑(2‑benzthiazolylthio)‑1‑propanesulfonsäure (ZPS), is used as an accelerator and formulated with a suppressor (polyethylene glycol, PEG) and chloride ions (Cl−) in the copper plating solution containing electrolytes (Cu sulfate and sulfuric acid) to prepare the Cu films. Microstructural characterization using focus ion beam (FIB), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) reveals that an increase of the ZPS concentration accelerates the grain growth of the electroplated Cu films. Impurity examination based on time-of-flight secondary ion mass spectrometer (TOF-SIMS) shows that such microstructural evolution effectively suppresses the impurity incorporation in the electroplated Cu films. The suppression effect on impurity incorporation by using a high level of ZPS concentration plays an important role in retaining the microstructural stability and integrity of the electroplated Cu solder joints subjected to thermal aging.

Does interfacial photochemistry play a role in the photolysis of pyruvic acid in water?

Pyruvic acid (PA) exists in fogs, aerosols and clouds. The photochemistry-driven reaction pathways of PA in the aqueous phase are more elusive than the gas phase. The PA photochemical process may occur in the bulk liquid phase and at the air-liquid interface in ambient conditions. We conducted two sample preparation methods to simulate two possible scenarios: the air-liquid interface and the bulk liquid phase under photolysis. Time-of-flight secondary ion mass spectrometer (ToF-SIMS) was used to analyze samples because of its high sensitivity and mass accuracy in surface analysis. Both negative and positive ion mode mass spectra provide complementary information of the products under different reaction conditions. Spectral principal component analysis (PCA) is used to determine similarities and differences among various samples. The air-liquid interface facilitates more radical reactions and form higher molecular weight compounds (HMWCs) more quickly than the bulk liquid phase, which mainly has non-radical reactions such as anhydride reactions and decarboxylation reactions. Our results show that interfacial chemistry plays an important role in atmospheric scenarios. Moreover, different types of secondary organic aerosols (SOAs) are formed, suggesting the strong influence of interfacial photochemistry has on the earth atmosphere.