Ion Gun Research Articles

Relative secondary ion yields produced by vacuum-type electrospray droplet ion beams

The relatively new electrospray droplet impact method is based on electrospray at atmospheric pressure and has been successful in achieving efficient desorption/ionization of biological molecules, soft etching of polymers, and nonselective etching of metal oxides. However, the beam current and brightness of this method are not practical for surface analyses. To improve the performance of this method, the authors have developed a new droplet ion beam gun using an electrospray of aqueous solutions in a vacuum. This technique could be expected to be a high-intensity massive cluster ion beam and they evaluate the performance of the vacuum-type electrospray droplet ion (V-EDI) gun. In this study, V-EDI and gas cluster ion beam guns were installed in a time-of-flight analyzer to directly compare the relative secondary ion yields of several biomolecules produced by several cluster ion beams.

Ag+ ion emission from a sharp Ag2O-Al2O3-P2O5-SiO2 glass-fiber emitter

Ag+ ion conducting xAg2O·(30 − x)Al2O3·55P2O5·15SiO2 (x = 20 and 25, mol%) glasses were prepared using a conventional melting method, and structures and glass transition temperature were investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC), ultraviolet-visible (UV–Vis) and Fourier transform infrared (FTIR) spectroscopies. Impedance measurement reveals the glass with x = 25 shows a high Ag+ ion conductivity of 3 × 10−3 S cm−1 at 300 °C. Ag+ ion emission measurement was carried out using a sharpened glass fiber tip less than 1 μm, and the emission current was successfully observed above the acceleration voltage of 4 kV at 300 °C and 4 × 10−5 Pa. Silver particles were confirmed on the target substrate after the Ag+ emission measurement. A good linear correlation is obtained between log(current) and square root of the voltage, suggesting the emission of Ag+ ion from the tip of glass fiber is expressed by Schottky model. In this ion emission method, a plasma is not required for ionization and the ion emission mechanism is simple, and various ion conducting glasses can be applied for the emitter of ion gun.

Characterization of Mega-Dalton-Sized Nanoparticles by Superconducting Tunnel Junction Cryodetection Mass Spectrometry.

The characterization of nanomaterials is critical to understand the size/structure-dependent properties of these particles. In this report, a form of heavy ion mass spectrometry, namely, superconducting tunnel junction (STJ) cryodetection mass spectrometry (MS) is used to characterize quantum dot semiconductor nanocrystals and gold nanoparticles. The nanoparticles studied ranged in mass from 200 kDa to >1.5 MDa and included lead sulfide quantum dots, various cadmium selenide and/or telluride-based core-shell quantum dots coated with different ligands, and gold nanoparticles. Nanoparticles were ionized by both matrix-assisted laser desorption ionization (MALDI) and laser desorption ionization (LDI), shot with an aimed ion gun into a flight tube, mass separated by time-of-flight (TOF), and detected by an energy-sensitive STJ cryodetector. STJ cryodetection MS can be used to analyze intact heterogeneous nanoparticles, allowing determination of average particle mass, dispersity, and ligand loading. Some nanoparticles, however, do undergo fragmentation during the MALDI or LDI-TOF mass analyses. The measurement of the energy deposited into the detector was found to be different for different types of particles. Metastable fragments from these nanoparticles were observed at lower energies. The lower energies deposited for metastable fragments can provide insight into the stability and surface compositions of these materials. Cadmium selenide core-shell quantum dots (655 nm emission) conjugated to biomacromolecules, such as cholera toxin B and human serum transferrin, were also analyzed. When compared to unconjugated particles by mass, it was determined that ∼96 cholera toxin B and ∼14 transferrin proteins were attached to the surface of these nanoparticles.

Liquid-Phase Ion Gun for Local Acidification of Na2S Aqueous Solution and Local Sulfidation of Fe-Cr Alloy Surface

Local sulfidation of Fe-Cr alloy surfaces was attempted by using a liquid-phase ion gun (LPIG), in which a platinum microelectrode was anodically polarized in the vicinity of the alloy surface in 0.1 M Na2S aqueous solution. An increase in H+-concentration, namely local acidification, of the solution in the narrow space between the microelectrode and alloy surface successfully induced the formation of an H2S-concentrated environment and resulted in local sulfidation of the Fe-Cr alloy surface. The degree of sulfidation was dependent on acidification conditions such as the microelectrode current, specimen electrode potential and Cr concentration of the alloy. The use of an LPIG enables a sulfidation test not only to restrict the amount of H2S generated but also to evaluate sulfidation of a material surface quantitatively.

Some microelectrochemical methods for the investigation of passivity and corrosion

Abstract Microelectrochemical approaches using a microcapillary cell (MCC), scanning electrochemical microscopy (SECM), and in situ ellipsomicroscopy for studying heterogeneous passive or corroding surfaces of materials are reviewed. An MCC can be used to investigate the localized behavior of a site of interest on a material by various electrochemical methods, including electrochemical impedance spectroscopy. SECM has often been used for imaging corroding surfaces or passive films on materials. Moreover, the use of a liquid-phase ion gun, a mode of SECM that forms a local aggressive environment at the solution/material interphase, can reveal the depassivation mechanism and kinetics of the surface of a material. The heterogeneous growth or degradation of a thin passive film on a material has been monitored using in situ ellipsomicroscopy, and a depassivation site has been successfully found before a film breakdown is initiated. These microelectrochemical methods are useful for monitoring the heterogeneous distribution of a passive film and for investigating the heterogeneity of the passivity of materials.

Preliminary Results of He Implantation in Tungsten at Angled Incidence in DAISIE

A new experimental facility at the University of Wisconsin-Madison, the Dual-Advanced Ion Simultaneous Implantation Experiment (DAISIE), has been designed and constructed to examine tungsten surface damage phenomena. These include microstructure formation and erosion due to helium bombardment as well as the retention of hydrogen gas while under the simultaneous bombardment of helium and deuterium ion beams, as would occur in ITER or other deuterium-burning fusion devices. DAISIE features two ion guns angled at 55° to the sample normal. These guns are independent with respect to beam current, allowing for a high degree of control over the separate D and He beams fluxes and fluences and the composition ratio of these ions impinging upon the tungsten sample surface. Preliminary results are available for helium-only implantations at energies of 30 keV to average fluences of 3 × 1018 He/cm2 in tungsten samples at temperatures of 900°C. As in prior experiments, surface damage appears to be highly-dependent on the crystallography of the individual grains. although a distinct set of helium-induced microstructures from past experiments is observed. Erosion yield is consistent with prior, similar helium irradiation experiments at the University of Wisconsin, but exceeds that predicted by physical sputtering yields and other past sputtering experiments.

Liquid-Phase Ion Gun Technique for Degradation and Evaluation of Oxide Films

Liquid-phase ion gun, which was named by Prof. Masahiro Seo, is an effective corrosion research tool. It is a kind of applications of scanning electrochemical microscopy (SECM), that is a scanning probe technique as same as a double electrode technique such as a rotating ring disk electrode. In the case of SECM, a tip microelectrode and a specimen substrate electrode work as a generator and a collector of electroactive species. In the first setup of LPIG, a silver microelectrode covered with silver chloride was used as the tip electrode. Though silver chloride is insoluble products in aqueous solution at room temperature, it is easily reduced to silver and generates Cl– by cathodic polarization of the electrode. Concentration of Cl– in the narrow space between tip electrode and substrate is majorly obeyed by the diffusion when the solution with highly concentrated electrolyte is in stagnant. Thus, LPIG allows controlling the local concentration of Cl– in the vicinity of specified substrate surface. It was used to induce the de-passivation and to investigate the effect of Cl– on breakdown of the passive film on substrate iron. Here, the principle and concept of LPIG as a generator of Cl– are reviewed and the derivative usage of LPIG as a generator of HS– is discussed.

真空エレクトロスプレーを用いるイオン銃の開発

Atmospheric pressure electrospray had been used previously in our laboratory to generate massive cluster ion beam for charged droplet ionization; a method we called electrospray droplet impact (EDI). Previous ion gun that employed atmospheric pressure electrospray lacks adequate beam current and density for surface and interface analysis. To improve the EDI beam performance, we have proposed a technique for producing a stable electrospray of aqueous solution under vacuum. It is well known that vacuum electrospray of volatile liquids is difficult because of the freezing of the liquids by evaporative cooling under vacuum. Vacuum electrospray of aqueous solution was achieved by irradiating the tip of the electrospray emitter with infrared or near-infrared laser to prevent the freezing under high vacuum (<0.05 Pa). A stable and large beam current was also obtained by optimizing the vacuum electrospray conditions. On the basis of these results, the vacuum electrospray can be expected to be a high-performance massive cluster ion gun.

Comparison of Se and Te clusters produced by ion bombardment

Nanostructures based on tellurium and selenium are materials used as components for the manufacturing topological insulators. Therefore it is crucial to precisely characterize these materials. In this work the emission of selenium and tellurium cluster ions, sputtered by Bi+ primary ion guns, was investigated by using Time-of-Flight Secondary Ion Mass Spectrometry (TOF SIMS). It has been found that Bix Tex and Bix Sex clusters appear in addition to Sex and Tex clusters in the mass range up to ~ 1300 m/z. Local maxima or minima (magic numbers) are observed in the ion intensity versus a number of atoms per cluster for both positive and negative ions spectra for all types of clusters and primary ions used. These extrema can be attributed to different yield and stability of certain clusters but also to fragmentation of high-mass clusters.

Initiation of Localized Corrosion of Ferritic Stainless Steels by Using the Liquid-Phase Ion Gun Technique

The initiation of localized corrosion of types 430 and 443J1 ferritic stainless steels was evaluated in 0.15 mol dm−3 Na2SO4 solution. A liquid-phase ion gun (LPIG), a silver microelectrode covered with a silver chloride layer, was cathodically polarized to generate Cl− in the vicinity of the stainless steel polarized at 0.4 VSSE. Contact of the stainless steel surface with the Cl−-concentrated environment by the LPIG operation induced a rapid increase in anodic current flow through the stainless steel electrode after the induction period td and consumption of the cathodic electric charge Qd by the LPIG microelectrode. Numerical modeling using the LPIG microelectrode current for td gave a critical Cl− concentration [Cl−]d needed for the initiation of localized corrosion. These parameters obtained by LPIG tests showed that type 443J1 stainless steel was superior to type 430 stainless steel in localized corrosion resistance. AES depth profiling of the stainless steel surfaces after the LPIG operation revealed enrichment of Cl in the outermost oxide film as well as decreased film thickness. The mechanism of degradation of the stainless steel surface due to contact with the Cl−-concentrated solution is discussed. The adsorption of Cl− on the oxide surface is thought to be a trigger of the oxide degradation.

Secondary ion yields for vacuum-type electrospray droplet beams measured with a triple focus time-of-flight analyzer.

We previously developed a massive cluster ion beam gun for secondary ion mass spectrometry (SIMS) in which the primary beam source is a vacuum electrospray. The secondary ion yields produced by this method had not yet been measured with a commercial time-of-flight (TOF) secondary ion mass spectrometer, and the ionization performance was unknown. A vacuum-type electrospray droplet ion gun was connected to a triple-focus TOF analyzer. The flight time of the secondary ions was measured using a sample-bias pulsing method, because a short pulse of the electrospray droplet beam could not be obtained. The secondary ion yields of an amino acid sample produced by the electrospray droplet beams and atomic Ga ion beams were compared. TOF secondary ion spectra were measured for the amino acid and peptide samples with a mass resolution of ~500 using the sample-bias pulsing method. The secondary ion yield of the amino acid sample produced with the 10 kV vacuum-type electrospray droplet beams was much higher than that produced by 10 kV Ga ion beams. In addition, the secondary ion yields for the peptide sample and amino acid samples were almost similar. This is the first report on secondary ion yields produced with vacuum-type electrospray droplet ion beams and measured with a semi-commercial TOF analyzer. The enhancement of secondary ion yields, in particular for relatively high-mass molecules, would be very useful in the SIMS analysis of a wide variety of biological samples. Copyright © 2016 John Wiley & Sons, Ltd.

Food-induced changes of lipids in rat neuronal tissue visualized by ToF-SIMS imaging.

Time of flight secondary ion mass spectrometry (ToF-SIMS) was used to image the lipid localization in brain tissue sections from rats fed specially processed cereals (SPC). An IonTof 5 instrument equipped with a Bi cluster ion gun was used to analyze the tissue sections. Data from 15 brain samples from control and cereal-fed rats were recorded and exported to principal components analysis (PCA). The data clearly show changes of certain lipids in the brain following cereal feeding. PCA score plots show a good separation in lipid distribution between the control and the SPC-fed group. The loadings plot reveal that the groups separated mainly due to changes in cholesterol, vitamin E and c18:2, c16:0 fatty acid distribution as well as some short chain monocarboxylic fatty acid compositions. These insights relate to the working mechanism of SPC as a dietary supplement. SPC is thought to activate antisecretory factor (AF), an endogenous protein with regulatory function for inflammation and fluid secretion. These data provide insights into lipid content in brain following SPC feeding and suggest a relation to activating AF.

The materials irradiation experiment for testing plasma facing materials at fusion relevant conditions.

The Materials Irradiation Experiment (MITE-E) was constructed at the University of Wisconsin-Madison Inertial Electrostatic Confinement Laboratory to test materials for potential use as plasma-facing materials (PFMs) in fusion reactors. PFMs in fusion reactors will be bombarded with x-rays, neutrons, and ions of hydrogen and helium. More needs to be understood about the interactions between the plasma and the materials to validate their use for fusion reactors. The MITE-E simulates some of the fusion reactor conditions by holding samples at temperatures up to 1000 °C while irradiating them with helium or deuterium ions with energies from 10 to 150 keV. The ion gun can irradiate the samples with ion currents of 20 μA-500 μA; the typical current used is 72 μA, which is an average flux of 9 × 10(14) ions/(cm(2) s). The ion gun uses electrostatic lenses to extract and shape the ion beam. A variable power (1-20 W), steady-state, Nd:YAG laser provides additional heating to maintain a constant sample temperature during irradiations. The ion beam current reaching the sample is directly measured and monitored in real-time during irradiations. The ion beam profile has been investigated using a copper sample sputtering experiment. The MITE-E has successfully been used to irradiate polycrystalline and single crystal tungsten samples with helium ions and will continue to be a source of important data for plasma interactions with materials.

In situ ion beam sputter deposition and X‐ray photoelectron spectroscopy (XPS) of multiple thin layers under computer control for combinatorial materials synthesis

Deposition of ultra‐thin layers under computer control is a frequent requirement in studies of novel sensors, materials screening, heterogeneous catalysis, the probing of band offsets near semiconductor junctions and many other applications. Often large‐area samples are produced by magnetron sputtering from multiple targets or by atomic layer deposition (ALD). Samples can then be transferred to an analytical chamber for checking by X‐ray photoelectron spectroscopy (XPS) or other surface‐sensitive spectroscopies. The ‘wafer‐scale’ nature of these tools is often greater than is required in combinatorial studies, where a few square centimetres or even millimetres of sample is sufficient for each composition to be tested. The large size leads to increased capital cost, problems of registration as samples are transferred between deposition and analysis, and often makes the use of precious metals as sputter targets prohibitively expensive. Instead we have modified a commercial sample block designed to perform angle‐resolved XPS in a commercial XPS instrument. This now allows ion‐beam sputter deposition from up to six different targets under complete computer control. Ion beam deposition is an attractive technology for depositing ultra‐thin layers of great purity under ultra‐high vacuum conditions, but is generally a very expensive technology. Our new sample block allows ion beam sputtering using the ion gun normally used for sputter depth‐profiling of samples, greatly reducing the cost and allowing deposition to be done (and checked by XPS) in situ in a single instrument. Precious metals are deposited cheaply and efficiently by ion‐beam sputtering from thin metal foils. Samples can then be removed, studied and exposed to reactants or surface treatments before being returned to the XPS to examine and quantify the effects. Copyright © 2016 The Authors Surface and Interface Analysis Published by John Wiley &amp; Sons Ltd.

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS): A New Tool for the Analysis of Toxicological Effects on Single Cell Level.

Single cell imaging mass spectrometry opens up a complete new perspective for strategies in toxicological risk assessment and drug discovery. In particular, time-of-flight secondary ion mass spectrometry (ToF-SIMS) with its high spatial and depth resolution is becoming part of the imaging mass spectrometry toolbox used for single cell analysis. Recent instrumentation advancements in combination with newly developed cluster ion guns allow 3-dimensional reconstruction of single cells together with a spatially resolved compound location and quantification on nanoscale depth level. The exact location and quantification of a single compound or even of a set of compounds is no longer restricted to the two dimensional space within single cells, but is available for voxels, a cube-sized 3-dimensional space, rather than pixels. The information gathered from one voxel is further analysed using multivariate statistical methodology like maximum autocorrelation factors to co-locate the compounds of interest within intracellular organelles like nucleus, mitochondria or golgi apparatus. Furthermore, the cell membrane may be resolved, including adhering compounds and potential changes of the lipid patterns. The generated information can be used further for a first evaluation of intracellular target specifity of new drug candidates or for the toxicological risk assessment of environmental chemicals and their intracellular metabolites. Additionally, single cell lipidomics and metabolomics enable for the first time an in-depth understanding of the activation or inhibition of cellular biosynthesis and signalling pathways.

In situ ion gun cleaning of surface adsorbates and its effect on electrostatic forces

To obtain precise measurements of the Casimir force, it is crucial to take into account the electrostatic interactions that exist between the two boundaries. Two otherwise grounded conductors will continue to have residual electrostatic effects from patch potentials existing on the surfaces. In this paper, we look at the effect of in situ cleaning of adsorbate patches, and the resultant effect on the net electrostatic potential difference between two surfaces. We find a significant reduction in the residual potential due to in situ Ar[Formula: see text] cleaning for the samples used.

Cryo-planing of frozen-hydrated samples using cryo triple ion gun milling (CryoTIGM™).

Cryo-SEM is a high throughput technique for imaging biological ultrastructure in its most pristine state, i.e. without chemical fixation, embedding, or drying. Freeze fracture is routinely used to prepare internal surfaces for cryo-SEM imaging. However, the propagation of the fracture plane is highly dependent on sample properties, and the resulting surface frequently shows substantial topography, which can complicate image analysis and interpretation. We have developed a broad ion beam milling technique, called cryogenic triple ion gun milling (CryoTIGM™ ['krī-ə-,tīm]), for cryo-planing frozen-hydrated biological specimens. Comparing sample preparation by CryoTIGM™ and freeze fracture in three model systems, Baker's yeast, mouse liver tissue, and whole sea urchin embryos, we find that CryoTIGM™ yields very large (∼700,000 μm(2)) and smooth sections that present ultrastructural details at similar or better quality than freeze-fractured samples. A particular strength of CryoTIGM™ is the ability to section samples with hard-soft contrast such as brittle calcite (CaCO3) spicules in the sea urchin embryo.

Development of Wien filter for small ion gun of surface analysis.

The gas cluster ion beam (GCIB) and liquid metal ion beam have been studied in the context of ion beam usage for analytical equipment in applications such as X-ray photoelectron spectroscopy and secondary ion mass spectroscopy (SIMS). In particular, small ion sources are used for the secondary ion generation and ion etching. To set the context to this study, the SIMS project has been launched to develop ion-gun based analytical equipment for the Korea Basic Science Institute. The objective of the first stage of the project is the generation of argon beams with a GCIB system [A. Kirkpatrick, Nucl. Instrum. Methods Phys. Res., Sect. B 206, 830-837 (2003)] that consists of a nozzle, skimmer, ionizer, acceleration tube, separation system, transport system, and target. The Wien filter directs the selected cluster beam to the target system by exploiting the velocity difference of the generated particles from GCIB. In this paper, we present the theoretical modeling and three-dimensional electromagnetic analysis of the Wien filter, which can separate Ar(+) 2500 clusters from Ar(+) 2400 to Ar(+) 2600 clusters with a 1-mm collimator.

Depth Profile Analysis of Phosphorus Implanted SiC Structures

Secondary ion mass spectrometry depth profile analyses were performed on two sets of 4H-SiC(0001) substrate samples implanted with phosphorus. Both sets were processed under the same conditions. We implanted the samples with 100 keV (10(11)-10(14) cm(-2)) phosphorus ions through the thin chemical vapor deposition deposited silicon dioxide stopping mask in order to obtain an ultra-shallow implantation profile. After phosphorus implantation, secondary ion mass spectrometry depth profile analysis was performed on the first set of samples and the second set was subjected to thermal oxidation procedure at 1200 degrees C in order to create a dielectric layer. The aim of the oxidation process was formation of the silicon dioxide layer enriched with phosphorus: the element, which is considered to be suitable for trap density reduction. Ion implantation parameters as well as oxidation and chemical etching procedures were examined for the proper incorporation of phosphorus into the subsurface structure of the silicon oxide. Secondary ion mass spectrometry depth profile analysis was performed with Physical Electronics 06-350E sputter ion gun and QMA-410 Balzers quadrupole mass analyser. The analytical parameters such as: 1.7 keV Ar+ ion beam digitally scanned over 3 x 3 mm(2) area and ion erosion rate of 1.4 nm/min and sampling rate of 0.3 nm, were suitable for samples oxidized after ion implantation.

Large Area Cryo-Planing of Vitrified Samples Using Broad-Beam Ion Milling.

On account of its excellent resolution and high throughput, cryoSEM imaging has recently seen resurgence. In this work, we report on the development of cryogenic triple ion gun milling (CryoTIGM™), a broad ion beam milling technique for cryo-planing of vitrified, "frozen-hydrated" specimens. We find that sections prepared with CryoTIGM™ are smooth over exceptionally large areas (~700,000 µm2), and reveal ultrastructural details in similar or better quality than freeze-fractured samples.