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Recent studies have demonstrated the existence of a discrete pool of cholesterol in the plasma membranes (PM) of mammalian cells-referred to as the accessible cholesterol pool-that can be detected by the binding of modified versions of bacterial cytolysins (e.g., anthrolysin O). When the amount of accessible cholesterol in the PM exceeds a threshold level, the excess cholesterol moves to the endoplasmic reticulum (ER), where it regulates the SREBP2 pathway and undergoes esterification. We reported previously that the Aster/Gramd1 family of sterol transporters mediates nonvesicular movement of cholesterol from the PM to the ER in multiple mammalian cell types. Here, we investigated the PM pool of accessible cholesterol in cholesterol-loaded fibroblasts with a knockdown of Aster-A and in mouse macrophages from Aster-B and Aster-A/B-deficient mice. Nanoscale secondary ion mass spectrometry (NanoSIMS) analyses revealed expansion of the accessible cholesterol pool in cells lacking Aster expression. The increased accessible cholesterol pool in the PM was accompanied by reduced cholesterol movement to the ER, evidenced by increased expression of SREBP2-regulated genes. Cosedimentation experiments with liposomes revealed that the Aster-B GRAM domain binds to membranes in a cholesterol concentration-dependent manner and that the binding is facilitated by the presence of phosphatidylserine. These studies revealed that the Aster-mediated nonvesicular cholesterol transport pathway controls levels of accessible cholesterol in the PM, as well as the activity of the SREBP pathway.

Covering: 2009-2019 Over the last decade, methods in imaging mass spectrometry (IMS) have progressively improved and diversified toward a variety of applications in natural products research. Because IMS allows for the spatial mapping of the production and distribution of biologically active molecules in situ, it facilitates phenotype and organelle driven discovery efforts. As practitioners of IMS for natural products discovery, we find one of the most important aspects of these experiments is the sample preparation and compatibility with different ionization sources that are available to a given researcher. As such, we have focused this mini review to cover types of ionization sources that have been used in natural products discovery applications and provided concrete examples of use for natural products discovery while discussing the advantages and limitations of each method. We aim for this article to serve as a resource to guide the broader natural product community interested in IMS toward the application/method that would best serve their natural product discovery needs given the sample and analyte(s) of interest. This mini review has been limited to applications using natural products and thus is not exhaustive of all possible ionization methods which have only been applied to image other types of samples such as mammalian tissues. Additionally, we briefly review how IMS has been coupled with other imaging platforms, such as microscopy, to enhance information outputs as well as offer our future perspectives on the incorporation of IMS in natural products discovery.

Heterogeneity in the metabolic properties of adipocytes in white adipose tissue has been well documented. We sought to investigate metabolic heterogeneity in adipocytes of brown adipose tissue (BAT), focusing on heterogeneity in nutrient uptake. To explore the possibility of metabolic heterogeneity in brown adipocytes, we used nanoscale secondary ion mass spectrometry (NanoSIMS) to quantify uptake of lipids in adipocytes interscapular BAT and perivascular adipose tissue (PVAT) after an intravenous injection of triglyceride-rich lipoproteins (TRLs) containing [2H]triglycerides (2H-TRLs). The uptake of deuterated lipids into brown adipocytes was quantified by NanoSIMS. We also examined 13C enrichment in brown adipocytes after administering [13C]glucose or 13C-labeled mixed fatty acids by gastric gavage. The uptake of 2H-TRLs-derived lipids into brown adipocytes was heterogeneous, with 2H enrichment in adjacent adipocytes varying by more than fourfold. We also observed substantial heterogeneity in 13C enrichment in adjacent brown adipocytes after administering [13C]glucose or [13C]fatty acids by gastric gavage. The uptake of nutrients by adjacent brown adipocytes within a single depot is variable, suggesting that there is heterogeneity in the metabolic properties of brown adipocytes.

Macrophages are generally assumed to unload surplus cholesterol through direct interactions between ABC transporters on the plasma membrane and HDLs, but they have also been reported to release cholesterol-containing particles. How macrophage-derived particles are formed and released has not been clear. To understand the genesis of macrophage-derived particles, we imaged mouse macrophages by EM and nanoscale secondary ion mass spectrometry (nanoSIMS). By scanning EM, we found that large numbers of 20- to 120-nm particles are released from the fingerlike projections (filopodia) of macrophages. These particles attach to the substrate, forming a "lawn" of particles surrounding macrophages. By nanoSIMS imaging we showed that these particles are enriched in the mobile and metabolically active accessible pool of cholesterol (detectable by ALO-D4, a modified version of a cholesterol-binding cytolysin). The cholesterol content of macrophage-derived particles was increased by loading the cells with cholesterol or by adding LXR and RXR agonists to the cell-culture medium. Incubating macrophages with HDL reduced the cholesterol content of macrophage-derived particles. We propose that release of accessible cholesterol-rich particles from the macrophage plasma membrane could assist in disposing of surplus cholesterol and increase the efficiency of cholesterol movement to HDL.

The processing of triglyceride-rich lipoproteins (TRLs) in capillaries provides lipids for vital tissues, but our understanding of TRL metabolism is limited, in part because TRL processing and lipid movement have never been visualized. To investigate the movement of TRL-derived lipids in the heart, mice were given an injection of [2H]triglyceride-enriched TRLs, and the movement of 2H-labeled lipids across capillaries and into cardiomyocytes was examined by NanoSIMS. TRL processing and lipid movement in tissues were extremely rapid. Within 30 s, TRL-derived lipids appeared in the subendothelial spaces and in the lipid droplets and mitochondria of cardiomyocytes. Enrichment of 2H in capillary endothelial cells was not greater than in cardiomyocytes, implying that endothelial cells may not be a control point for lipid movement into cardiomyocytes. Remarkably, a deficiency of the putative fatty acid transport protein CD36, which is expressed highly in capillary endothelial cells, did not impede entry of TRL-derived lipids into cardiomyocytes.

Copper is essential for eukaryotic life, and animals must acquire this nutrient through the diet and distribute it to cells and organelles for proper function of biological targets. Indeed, mutations in the central copper exporter ATP7A contribute to a spectrum of diseases, including Menkes disease, with symptoms ranging from neurodegeneration to lax connective tissue. As such, a better understanding of the fundamental impacts of ATP7A mutations on in vivo copper distributions is of relevance to those affected by these diseases. Here we combine metal imaging and optical imaging techniques at a variety of spatial resolutions to identify tissues and structures with altered copper levels in the Calamitygw71 zebrafish model of Menkes disease. Rapid profiling of tissue slices with LA-ICP-MS identified reduced copper levels in the brain, neuroretina, and liver of Menkes fish compared to control specimens. High resolution nanoSIMS imaging of the neuroretina, combined with electron and confocal microscopies, identified the megamitochondria of photoreceptors as loci of copper accumulation in wildtype fish, with lower levels of megamitochondrial copper observed in Calamitygw71 zebrafish. Interestingly, this localized copper decrease does not result in impaired photoreceptor development or altered megamitochondrial morphology, suggesting the prioritization of copper at sufficient levels for maintaining essential mitochondrial functions. Together, these data establish the Calamitygw71 zebrafish as an optically transparent in vivo model for the study of neural copper misregulation, illuminate a role for the ATP7A copper exporter in trafficking copper to the neuroretina, and highlight the utility of combining multiple imaging techniques for studying metals in whole organism settings with spatial resolution.

H 2 O:C 2 H 6 ice mixture, in a proportion of approximately 1:10 and at 60 K in average, is irradiated by energetic multicharged ions (≈ 65 MeV 252Cf fission fragments). The sputtered positive and negative secondary ions are analyzed by time-of-flight plasma desorption mass spectrometry (PDMS-TOF). Several ionic species are identified, indicating strong surface fragmentation and clusterization. The bombardment induces the formation of the ion cluster series: (CH 2) n X, where X = CH 3 + , C 2 H 6 + or CH + , and the carbon cluster series (C) n X, where X = CH 3 + or CH −. It is found that, in general, the yield distributions exhibit exponential decays, Y = Y 0 F e x p (− k F n) + Y 0 S e x p (− k S n) , where k F =1.11 u−1 and k S =0.11 u−1. Such finding may be useful to understand the processes by which, in cosmic space, ionized molecular species of hydrocarbons are delivery to the gas phase. [ABSTRACT FROM AUTHOR]

High entropy alloys are a promising new class of metal alloys with outstanding radiation resistance and thermal stability. The interaction with hydrogen might, however, have desired (H storage) or undesired effects, such as hydrogen-induced embrittlement or tritium retention in the fusion reactor wall. High entropy alloy WMoTaNbV and bulk W samples were used to study the quantity of irradiation-induced trapping sites and properties of D retention by employing thermal desorption spectrometry, secondary ion mass spectrometry, and elastic recoil detection analysis. The D implantation was not found to create additional hydrogen traps in WMoTaNbV as it does in W, while 90 at% of implanted D is retained in WMoTaNbV, in contrast to 35 at% in W. Implantation created damage predicted by SRIM is 0.24 dpa in WMoTaNbV, calculated with a density of 6.044 × 10 22 atoms/cm 3 . The depth of the maximum damage was 90 nm. An effective trapping energy for D in WMoTaNbV was found to be about 1.7 eV, and the D emission temperature was close to 700 °C. [ABSTRACT FROM AUTHOR]

Over the past few decades, several approaches have been used to image lipids in cells and tissues, but most have limited spatial resolution and sensitivity. Here, we discuss a relatively new approach, nanoscale secondary ion mass spectrometry imaging, that makes it possible to visualize lipids in cells and tissues in a quantitative fashion and with high spatial resolution and high sensitivity.

Cholesterol is a crucial lipid within the plasma membrane of mammalian cells. Recent biochemical studies showed that one pool of cholesterol in the plasma membrane is "accessible" to binding by a modified version of the cytolysin perfringolysin O (PFO*), whereas another pool is sequestered by sphingomyelin and cannot be bound by PFO* unless the sphingomyelin is destroyed with sphingomyelinase (SMase). Thus far, it has been unclear whether PFO* and related cholesterol-binding proteins bind uniformly to the plasma membrane or bind preferentially to specific domains or morphologic features on the plasma membrane. Here, we used nanoscale secondary ion mass spectrometry (NanoSIMS) imaging, in combination with 15N-labeled cholesterol-binding proteins (PFO* and ALO-D4, a modified anthrolysin O), to generate high-resolution images of cholesterol distribution in the plasma membrane of Chinese hamster ovary (CHO) cells. The NanoSIMS images revealed preferential binding of PFO* and ALO-D4 to microvilli on the plasma membrane; lower amounts of binding were detectable in regions of the plasma membrane lacking microvilli. The binding of ALO-D4 to the plasma membrane was virtually eliminated when cholesterol stores were depleted with methyl-β-cyclodextrin. When cells were treated with SMase, the binding of ALO-D4 to cells increased, largely due to increased binding to microvilli. Remarkably, lysenin (a sphingomyelin-binding protein) also bound preferentially to microvilli. Thus, high-resolution images of lipid-binding proteins on CHO cells can be acquired with NanoSIMS imaging. These images demonstrate that accessible cholesterol, as judged by PFO* or ALO-D4 binding, is not evenly distributed over the entire plasma membrane but instead is highly enriched on microvilli.

Impacts of energetic C60 ions with energies of the order of MeV are excellent ionization methods for highly sensitive secondary ion (SI) mass spectrometry because they can provide SIs necessary for the identification of target materials in high emission yields with high reproducibility. As part of an investigation into their SI emission phenomena with the aim of controlling the mass-analyzed depth range, we measured and characterized the impact angle dependence of SI mass spectra for MeV C60 ion impacts, and found that shallower angle impacts of MeV C60 ions can provide surface-sensitive information through intense emission of surface-derived SIs. [ABSTRACT FROM AUTHOR]

The combined approach of incubating environmental samples with stable isotope-labeled substrates followed by single-cell analyses through high-resolution secondary ion mass spectrometry (NanoSIMS) or Raman microspectroscopy provides insights into the in situ function of microorganisms. This approach has found limited application in soils presumably due to the dispersal of microbial cells in a large background of particles. We developed a pipeline for the efficient preparation of cell extracts from soils for subsequent single-cell methods by combining cell detachment with separation of cells and soil particles followed by cell concentration. The procedure was evaluated by examining its influence on cell recoveries and microbial community composition across two soils. This approach generated a cell fraction with considerably reduced soil particle load and of sufficient small size to allow single-cell analysis by NanoSIMS, as shown when detecting active N2-fixing and cellulose-responsive microorganisms via (15)N2 and (13)C-UL-cellulose incubations, respectively. The same procedure was also applicable for Raman microspectroscopic analyses of soil microorganisms, assessed via microcosm incubations with a (13)C-labeled carbon source and deuterium oxide (D2O, a general activity marker). The described sample preparation procedure enables single-cell analysis of soil microorganisms using NanoSIMS and Raman microspectroscopy, but should also facilitate single-cell sorting and sequencing.

Despite recent advances in analytical and computational chemistry, lipid identification remains a significant challenge in lipidomics. Ion-mobility spectrometry provides an accurate measure of the molecules' rotationally averaged collision cross-section (CCS) in the gas phase and is thus related to ionic shape. Here, we investigate the use of CCS as a highly specific molecular descriptor for identifying lipids in biological samples. Using traveling wave ion mobility mass spectrometry (MS), we measured the CCS values of over 200 lipids within multiple chemical classes. CCS values derived from ion mobility were not affected by instrument settings or chromatographic conditions, and they were highly reproducible on instruments located in independent laboratories (interlaboratory RSD < 3% for 98% of molecules). CCS values were used as additional molecular descriptors to identify brain lipids using a variety of traditional lipidomic approaches. The addition of CCS improved the reproducibility of analysis in a liquid chromatography-MS workflow and maximized the separation of isobaric species and the signal-to-noise ratio in direct-MS analyses (e.g., "shotgun" lipidomics and MS imaging). These results indicate that adding CCS to databases and lipidomics workflows increases the specificity and selectivity of analysis, thus improving the confidence in lipid identification compared to traditional analytical approaches. The CCS/accurate-mass database described here is made publicly available.

White-nose syndrome (WNS) caused by the pathogenic fungus Pseudogymnoascus destructans is decimating the populations of several hibernating North American bat species. Little is known about the molecular interplay between pathogen and host in this disease. Fluorescence microscopy ambient ionization mass spectrometry was used to generate metabolic profiles from the wings of both healthy and diseased bats of the genus Myotis. Fungal siderophores, molecules that scavenge iron from the environment, were detected on the wings of bats with WNS, but not on healthy bats. This work is among the first examples in which microbial molecules are directly detected from an infected host and highlights the ability of atmospheric ionization methodologies to provide direct molecular insight into infection.

Stable isotopes are ideal labels for studying biological processes because they have little or no effect on the biochemical properties of target molecules. The NanoSIMS is a tool that can image the distribution of stable isotope labels with up to 50 nm spatial resolution and with good quantitation. This combination of features has enabled several groups to undertake significant experiments on biological problems in the last decade. Combining the NanoSIMS with other imaging techniques also enables us to obtain not only chemical information but also the structural information needed to understand biological processes. This article describes the methodologies that we have developed to correlate atomic force microscopy and backscattered electron imaging with NanoSIMS experiments to illustrate the imaging of stable isotopes at molecular, cellular, and tissue scales. Our studies make it possible to address 3 biological problems: (1) the interaction of antimicrobial peptides with membranes; (2) glutamine metabolism in cancer cells; and (3) lipoprotein interactions in different tissues.

Imaging mass spectrometry (IMS), based on linking mass-analysis data for ions and their original positions in a sample, allows the visualization of the spatial distribution of atomic and/or molecular species in the sample, and is therefore an essential analytical method for the characterization of chemical and biological materials. For sensitive elemental and chemical imaging using IMS, a sufficient amount of ions to be analyzed should be supplied from the analyzing area on the sample surface. Secondary ion mass spectrometry (SIMS) using energetic cluster ions (ECIs) with energies of sub-MeV and above as primary ions (ECI-SIMS) can provide the secondary ions necessary for the characterization of organic materials with high emission yields. Hence, ECI-SIMS is a good method for highly sensitive IMS. We report recent progress in ECI beam manipulation techniques for applications of ECI-SIMS to highly sensitive IMS together with the characteristics of ECI impacts on organic materials. [ABSTRACT FROM AUTHOR]

The impacts of C 60 ions on a poly(methyl methacrylate) target in the energy range of 0.12–0.54 MeV were characterized by analysis of negative secondary ion (N-SI) counting data measured using a time-of-flight secondary ion mass spectrometer combined with pulsed primary C 60 ion beams in an event-by-event counting mode. Analysis of the counting data was performed to obtain probability distributions of emitted N-SI numbers for one impact and the impact energy dependence of relative emission yields for selected N-SIs species. These emission properties obtained could be qualitatively explained in terms of the characteristics of the emission processes and ion track structures reported for C 60 impacts. [ABSTRACT FROM AUTHOR]

Neutron-induced secondary ions and their contribution to a single-event upset (SEU) in SRAM are investigated by Geant4 and TCAD simulations. It proves that the maximum linear energy transfer (LET) values of secondary ions produced by neutron–nuclear reactions can be as high as 31.5MeV-cm2/mg, while the LET value of 99.8% secondary ion is <16 MeV-cm2/mg. Only the secondary ion with the LET of >2 MeV-cm2/mg could induce an SEU in this 65-nm SRAM. Then, these results are used to calculate the atmospheric neutron-induced soft-error rate (SER). The calculated SER is verified by field testing and 14-MeV neutron-accelerated testing. [ABSTRACT FROM AUTHOR]

We have investigated the negative and positive secondary ions emitted from ethanol droplets by 4.0-MeV C 3+ impact to reveal the characteristic features of the reaction processes induced by fast heavy ions at the liquid ethanol surface. Analysis of the secondary ions was performed by time-of-flight mass spectrometry for microdroplet targets in a high vacuum environment. Fragment ions, deprotonated cluster ions, and trace amounts of the reaction product ions are observed in the negative secondary ions. The main fragment anions are C 2 H m O − ( m  = 1, 3, and 5) and C 2 H − generated by loss of hydrogen and oxygen atoms. The reaction product anions include deprotonated glycols, larger alcohols, and their dehydrated and dehydrogenated forms generated by secondary reactions between fragments and radicals. Furthermore, C 3 H m − ( m  = 0–2) and C 4 H m − ( m  = 0 and 1) are observed, which could be produced through a plasma state generated in the heavy ion track. Deprotonated ethanol cluster ions, [(EtOH) n  − H] − , are observed up to about n  = 25. [(EtOH) n  − H] − have smaller kinetic energies than the protonated cluster ions (EtOH) n H + . This probably represents the effect of the positive Coulomb potential transiently formed in the ion track. We also discuss the size distributions and structures of the water- and CH 2 OH-radical-attached ethanol cluster ions. [ABSTRACT FROM AUTHOR]

Secondary ion mass spectrometry (SIMS) was used to study the near-surface segregation of sulphur during; (a) the thermal processing stages (diffusion annealing after application of Pt bond coat and after secondary ageing following subsequent deposition of the YO-stabilised ZrO top coat) and (b) thermal cycling in the Ni-base superalloy, CMSX4. In the thermal processing stages, an increased segregation of sulphur was observed within the upper regions of the Pt bond coat after diffusion annealing, while following secondary ageing, the sulphur segregation in this layer became heterogeneous with discrete pockets of enrichment (≫1 ppm) and regions of depletion (≪1 ppm). During thermal cycling, partitioning of sulphur occurred to the Pt-enriched γ′ region characterised by the finger-like morphology, while examination of TBC spalled specimens showed significant depletion of sulphur within the substrate in the vicinity of the surface. The reservoir for sulphur-depletion within the substrate was definitively identified as the Pt-enriched γ′ region. A quantitative method for the calculation of sulphur-segregation at the surface in terms of mono-layers is presented. [ABSTRACT FROM AUTHOR]

Abstract: Energetic cluster ions with energies of the order of sub MeV or greater were applied to time-of-flight (TOF) secondary ion (SI) mass spectrometry. This gave various advantages including enhancement of SIs required for chemical structure characterization and prevention of charging effects in SI mass spectra for organic targets. We report some characteristic features of TOF SI mass spectrometry using energetic cluster ion impact ionization and discuss two future applications of it. [Copyright &y& Elsevier]

Abstract: We investigated the effects of size and energy of large incident Ar cluster ions on the secondary ion emission of Si. The secondary ions were measured using a double deflection method and a time-of-flight (TOF) technique. The size of the incident Ar cluster ions was between a few hundreds and several tens of thousands of atoms, and the energy up to 60keV. Under the incidence of keV energy atomic Ar ions, mainly atomic Si ions were detected, whereas Si cluster ions were rarely observed. On the other hand, under the incidence of large Ar cluster ions, the dominant secondary ions were (2⩽ n ⩽11). It has become clear that the yield ratio of secondary Si cluster ions was determined by the velocity of the incident cluster ions, and this strong dependence of the yield ratio on incident velocity should be related to the mechanisms of secondary ion emission under large Ar cluster ion bombardment. [Copyright &y& Elsevier]

Abstract: A mass spectrometric technique using nuclear microprobes is presented in this paper for biological applications. In recent years, imaging mass spectrometry has become an increasingly important technique for visualizing the spatial distribution of molecular species in biological tissues and cells. However, due to low yields of large molecular ions, the conventional secondary ion mass spectrometry (SIMS), that uses keV primary ion beams, is typically applied for imaging of either elements or low mass compounds. In this study, we performed imaging mass spectrometry using MeV ion beams collimated to about 10μm, and successfully obtained molecular ion images from plant and animal cell sections. The molecular ion imaging of the pollen section showed high intensities of ions in the pollen cytoplasm, compared to the pollen wall, and indicated the heterogeneous distribution in the cytoplasm. The 3T3-L1 cell image revealed the high intensity of ions, in particular from the cell nucleus. The result showed that not only the individual cell, but also the cell nucleus could be identified with the present imaging technique. [Copyright &y& Elsevier]

Abstract: We performed secondary ion mass spectrometry for arginine thin films in the incident energy range from 10keV to 2MeV, in which electronic energy loss in the surface region increases with energy and exceeds the nuclear energy loss. The yield of protonated arginine increased with incident energy, and at 2MeV it was approximately two orders of magnitude larger than at 10keV, where the nuclear collision process is dominant. It was found that the molecular ion desorption is enhanced by the electronic excitation induced in the near-surface region. In addition, the yield ratios of the fragment ions to the protonated arginine decreased with incident energy, which indicates that the nuclear energy deposition significantly affects molecular fragmentation. These results demonstrate a soft desorption and ionization of biomolecules by the MeV ion-induced electronic excitation. [Copyright &y& Elsevier]

Abstract: CO–NH3 ice at 25K is bombarded by 65MeV fission fragments and the emitted secondary ions are analyzed by time-of-flight mass spectrometry. The yields of the specific ion species (those formed only from CO or from NH3 molecules) and of the hybrid ion species (formed from both CO and NH3 molecules) are determined as a function of the ice temperature. The time-temperature dependence of desorption yields has been used for secondary ion identification because its behavior characterizes the ion''s origin around the sublimation temperature of CO ice (∼30K). The mass spectrum of positive ions measured before CO sublimation is decomposed into three spectra corresponding to CO specific ions, NH3 specific ions and hybrid molecular ions, respectively. The observed spectrum after CO sublimation is very similar to that of a pure NH3 specific spectrum. The total yield of all positive hybrid molecular ions over 600u mass range is found to be about 2 ions/impact: 20% of this is attributed to N and NH3 containing ions and 80% are ions having the C n O m Hl + structure. The ions C n≤3Hl,2,3 +, COH+, NO+, NH3OH+ and NH3CO+ were identified. At T =25K, the total yield of negative ions is about 20 times lower than that of positive ions, the most abundant species being the cyanide ion CN−. Observation of cluster ions based on (HCN) n indicates the formation of hydrogen cyanide. [Copyright &y& Elsevier]

Abstract: Secondary ions produced from a Si target bombarded with Ar cluster ions much larger than the molecular ions have been investigated. Secondary ions have been measured for a Si target bombarded with large Ar cluster ions at an incident energy between 7.5 and 27.5keV using a time-of-flight technique. The mean size of the Ar cluster ion was about 1000atoms/cluster, and then the collision energy per atom is between a few tens of eV and a few hundreds of eV. Secondary silicon cluster ions were detected under large Ar cluster ion bombardment. In this study, we succeeded to accurately measure the dependence of secondary ion spectra obtained by large Ar cluster ions on the incident cluster-ion size using a time-of-flight technique combined a primary-ion beam deflector and a secondary-ion deflector. The dependence of the secondary ion spectra under large Ar cluster ion bombardment on the incident cluster size is discussed. [Copyright &y& Elsevier]

Abstract: The yield and the mass distribution of positive-charged secondary ions emitted from a KCl(001) surface were measured when MeV heavy ions were incident on the surface at grazing angles θ i ranging from 1 to 5mrad. Specular reflection of the projectile ions allowed us to investigate secondary ion emission originating from purely electronic excitation of an insulator surface. Single-charged secondary ions such as Cl+, K+, and small clusters, (n =1–4) were detected for the incidence of 3MeV O2+, while no secondary ions were detectable for the incidence of 1MeV H+. The yield of secondary ions for the incidence of 3MeV O2+ slightly increased with the angle θ i. The secondary ion production rate P(x) as a function of the distance x between the projectile and the surface atomic plane was derived from the θ i-dependence of the yield. P(x) shows an overlinear dependence on the electronic stopping power S(x) for O ions specularly reflected in front of the surface. [Copyright &y& Elsevier]

Abstract: We propose to use cluster ions that are much larger than the molecular ions as primary ions for organic secondary ion mass spectrometry. Incident Ar cluster ion beams with energies from 10 to 20keV and a mean size of about 1000 atoms/cluster were used. Secondary ions were measured for a thin arginine film target (200nm) bombarded with large Ar cluster ions using a time-of-flight technique. Molecular ions of arginine and characteristic fragment ions were detected with high sensitivity. When large Ar cluster ions such as Ar1500 were incident on the arginine target, molecular ions of arginine were detected with little fragment ions. This indicates that large cluster ions can ionize arginine molecules without damaging them. [Copyright &y& Elsevier]

Abstract: We studied the secondary ion emission from arginine amino acid films bombarded with 500keV Au ions and compared the secondary ion intensities with those under 10keV Ar ion bombardment. A high sputtering yield of the protonated arginine ions (m/z 175) and a reduction in ion fragmentation were observed for 500keV Au ions. In addition, the molecular ion yield was compared to the yield measured with plasma desorption mass spectrometry (PDMS), and the data in this study did not show the tendency for the PDMS dependence. To the authors’ knowledge, this work is the first observation of the secondary ion emission for bio-molecular samples in the sub-MeV-energy range and the experimental results can give insights into the fundamental process of particle emission from bio-molecular samples. [Copyright &y& Elsevier]

Abstract: Surface oxidation of Si assisted by Ar cluster impact with a current density of a few μA/cm2 under O2 atmosphere was investigated. Thin-film formation by cluster ion beam presents a number of advantages such as atomic-scale surface smoothing, high density and precise stoichiometry. We used an Ar cluster ion beam with 20keV and a mean size of 1000 atoms per cluster and measured the emission yields of Si+ and SiO+ after Ar cluster ion irradiation in O2 atmosphere using a quadrupole mass spectrometer to investigate the dependence of Si surface oxidation on oxygen partial pressure. It was found that the Si surface was oxidized by Ar cluster ion irradiation in O2 atmosphere. [Copyright &y& Elsevier]

The present paper reports the effect of oxygen activity p(O2) on Nb segregation in a polycrystalline specimen of Nb doped TiO2 (2·91 at.-%). The determined segregation induced enrichment factor following annealing at 1773 K in p(O2) = 10 Pa and p(O2) = 21 kPa is 3·1 and 7·3 respectively. The data on the effect of p(O2) on the segregation induced Nb enrichment factor are considered in terms of defect disorder of Nb doped TiO2 and the related lattice charge neutrality requirements. The reported segregation data may be used for controlled modification of surface concentration gradients in TiO2 through the imposition of well defined gas phase composition during processing procedures. [ABSTRACT FROM AUTHOR]

The present paper reports the effect of oxygen activity p(O2) on Nb segregation in a polycrystalline specimen of Nb doped TiO2 (2·91 at.-%). The determined segregation induced enrichment factor following annealing at 1773 K in p(O2) = 10 Pa and p(O2) = 21 kPa is 3·1 and 7·3 respectively. The data on the effect of p(O2) on the segregation induced Nb enrichment factor are considered in terms of defect disorder of Nb doped TiO2 and the related lattice charge neutrality requirements. The reported segregation data may be used for controlled modification of surface concentration gradients in TiO2 through the imposition of well defined gas phase composition during processing procedures. [ABSTRACT FROM AUTHOR]

Abstract: Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25keV were used and the mean size of the Ar cluster ion was about 1000atoms/cluster. Si n + ions with n values up to n =8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size. [Copyright &y& Elsevier]

Abstract: Ion cluster desorption yields due to the impact of 252Cf fission fragments on condensed ammonia are determined. Identification and abundance of the ion desorbed species were provided by a time-of-flight mass spectrometer. Ammonia ice thin layers deposited on Au film were heated from 25K to complete sublimation. The typical pressure during heating process was 10−8 mbar. Measurements in the 25–150K temperature range show emission of (NH3) n NH m ± ion clusters, where n varies from 0 to ∼30 and m varies from 0 to 3 (for negative ions) or to 5 (for positive ions). The distribution is described by the sum of two decaying exponentials when n increases, which is interpreted by the simultaneous occurrence of two cluster formation regimes: (i) recondensation of sublimated molecules from the projectile track and (ii) emission of pre-formed bulk fragments from the periphery of the impact site. Moreover, the cluster yields of positive and negative ion series are approximately proportional to each other, suggesting that the ion cluster distribution shape is dictated by the neutral molecules but absolute yield is controlled by the emission of the ion species. In the 125–140K range, sublimation rate increases, the ice thickness decreases rapidly and all the mentioned cluster series tend to disappear. The series (HCN) n CN− then appears, originating in the clustering of residual hydrocarbon contaminants on the metal substrate surface. The residual gases are analyzed as a function of the NH3 ice target temperature and their partial pressure compared to the ion desorption yield. [Copyright &y& Elsevier]

Abstract: We have observed secondary particle emission in collision of HCI with Si and HOPG surfaces. For HOPG, we have measured the number of secondary electrons and the number of dot structures on the surface as the imprint of the incidence by STM. The single ion impact is surely observable with almost 100% efficiency by detecting an event of the secondary electron emission. For hydrogen terminated Si(111), H+, , , C+ and Si+ ions have been detected. The proton sputtering yield, which depends on the charge of HCI, has been examined. [Copyright &y& Elsevier]

Abstract: We have measured both secondary neutral and ionized particles from an InSb target under 3.0MeV Si ion bombardment. Measurements of both ions and neutrals have not been carried out so far in the MeV-energy range. The mass spectra and axial emission energy distributions of secondary particles were investigated. Secondary ions were measured with a linear- and a reflective-type time-of-flight technique, whereas secondary neutral particles were photo-ionized by a UV pulsed laser (ArF: 193nm) and measured with a reflective-type time-of-flight technique. Different results were obtained for neutral particles in comparison with ionized particles. The mean energy of neutral Sb atoms was much lower than that of neutral In atoms, whereas the mean energies of secondary In and Sb ions were nearly equal. [Copyright &y& Elsevier]

Masses, yields and emission energies of secondary ions have been systematically measured for solid targets bombarded by Si ions over an energy range between 0.5 and 5 MeV for studying roles of the electronic collision in the formation process of secondary atomic ions. The targets used were insulators (Al2O3, SiO2), semiconductors (Si, GaP, GaAs, GaSb and InSb) and a metal (Al). The obtained feature of the secondary ion emission depends characteristically on the target species. Singly and multiply charged positive ions are produced for Al, Si and P, respectively, from the Al, Al2O3, Si, SiO2 and GaP targets. In the cases of GaAs, GaSb and InSb, however, the production rates of positive As and Sb ions are strongly depressed. The obtained emission energy distributions of atomic ions from the conductor and the semiconductors are very broad and have gradually decaying tails at the high-energy side in contradiction to those of singly charged atomic and cluster ions from the insulators. The most probable and mean energies of atomic ions are proportional to their electric charge irrespective of the target conductivity. Large cluster ions are produced from the SiO2, Al2O3, GaSb and InSb targets. The yields of clusters from SiO2, GaSb and InSb show power-law dependences on their sizes and the yield of clusters from Al2O3 decreases exponentially with increasing size. These results show that the clusters from SiO2, GaSb and InSb are emitted directly from the surface. The clusters from Al2O3 may be indirectly produced by coagulation of molecules in a selvage region near the surface. [Copyright &y& Elsevier]

The interaction of elements near the interface during epitaxial growth of monocrystalline GaAs films through an aluminum layer is investigated by the methods of x-ray photoelectronic spectroscopy and secondary-ion mass spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: We measured the sputtering yield, surface roughness and surface damage of thin leucine films bombarded with Ar cluster ions and examined the usefulness of large gas cluster ions for the depth profiling of organic compounds. Ar cluster ion beams with a mean size of 2000atoms/cluster and energies from 5 to 30keV were used. Sputtering yields increased linearly with incident ion energy and were extremely high compared to inorganic materials. Surface damage was investigated by measuring positive secondary ions emitted from the leucine film before and after cluster ion irradiation. After irradiation the leucine surface became smoother. The yield ratio of protonated leucine ions to other fragment ions kept constant before and after Ar cluster ion irradiation. These results indicate that large gas cluster ions are useful for depth profiling of organic compounds. [Copyright &y& Elsevier]

Abstract: Si was bombarded with size-selected 40keV Ar cluster ions and positive secondary ions were measured using the time-of-flight technique under high and ultra-high vacuum (HV and UHV respectively) conditions. Si+ ions were main species detected under the incidence of 40keV Ar cluster ions, and the yields of Si cluster ions such as Si4 + were also extremely high under both conditions. On the other hand, oxidized secondary ions such as SiO+ were detected with high intensity only under the HV condition. The yield ratios of oxidized ions decreased in UHV to less than 1% of their values in HV. The effect of residual gas pressure on Si cluster ion yields is relatively low compared to oxidized ions, and the UHV condition is required to obtain accurate secondary ion yields. [Copyright &y& Elsevier]