Secondary Ion Mass Spectra Research Articles

Material Properties ofn‐Type β‐Ga2O3Epilayers with In Situ Doping Grown on Sapphire by Metalorganic Chemical Vapor Deposition

AbstractIn this study, in situ, Si‐doped heteroepitaxial Ga2O3layers are grown onc‐plane sapphire by metalorganic chemical vapor deposition. The X‐ray diffraction peaks of the doped Ga2O3epilayers shows ß‐phase of Ga2O3,and full width at half maximum of Ga2O3crystallinity is decreased at a Tetraethoxysilane (TEOS) molar flow rate of 2.23 × 10−7 mol min−1but increased with higher flow rates. The dopant concentrations of Ga2O3grown at 825 °C with TEOS molar flows of 2.23 × 10−7, 4.47 × 10−7, and 6.69 × 10−7 mol min−1are measured to be 5.5 × 1019, 1.1 × 1020, and 1.4 × 1020 atom cm−3, respectively, using secondary ion mass spectra and Hall measurements revealn‐type nature with carrier concentrations of 6.5 × 1017, 3.2 × 1018, and 3.9 × 1018atom/cm3, respectively. To increase Si dopant activation, Ga2O3growth temperature is raised to 875 °C. The result suggests a higher growth temperature can contribute to a greater probability of Si substitution on Ga lattice sites, which further reduces the resistivity of Ga2O3epilayer. Moreover, results are compared with theoretical Density Functional Theory studies.

In-situ spectral reflectance investigation of hetero-epitaxially grown β-Ga2O3 thin films on c-plane Al2O3 via MOVPE process

Metalorganic vapor-phase epitaxy of β-Ga2O3/c-plane Al2O3 heterostructures was monitored in-situ by spectral reflectance in different wavelengths. The reflectance spectrum was analysed as a function of the growth time and the incident wavelength to estimate the growth rate and the refractive index at the growth temperatures. The obtained values are validated by ex-situ methods such as secondary ion mass spectrum measurement and spectroscopic ellipsometry. A theoretical simulation of the reflectance spectrum was carried out by combining a transfer matrix method with a multilayer model, and a good agreement with the experimental results is presented.

Evaluation of Molecular Fragmentation in Polycyclic Aromatic Hydrocarbons by Time-of-Flight Secondary Ion Mass Spectrometry

In time-of-flight secondary ion mass spectrometry (TOF-SIMS), ionized molecules and molecular fragments (secondary ions) are generated in collisions of high-energy ions (primary ions) with a solid sample surface. Mass spectra of the emitted secondary ions are typically used to identify molecular species and to determine their spatial distribution on the sample surface. Here, we extend this application in a TOF-SIMS study of a series of polycyclic aromatic hydrocarbons (PAHs) where we focus on the fragmentation of these molecules, with the purpose of better understanding the fragmentation patterns of heavy aromatic molecules in petroleum. For all PAHs, the collision process generated (i) a series of smaller cation fragments and (ii) cations close in size to the original PAH (molecular cations). Stark differences are measured for various PAHs regarding the abundance of smaller fragments versus molecular cations. Observation of hydrogen-deficient (H-deficient) cation fragments indicates the formation of polyynes and allenes. For PAHs producing higher fractions of small cation fragments, these ions are surprisingly hydrogen rich (H-rich). The H/C ratio of fragments does not scale with the fraction of Clar sextet carbon, nor with energies of low-lying electronic transitions. Free radical cation fragments tend to be suppressed. For sufficiently large fragments, aromatic cations appear to be formed and include some free radical aromatics. There is ample production of molecular ions with loss of a single carbon atom or a methine group, which corresponds to the reduction of a 6-membered aromatic ring to a 5-membered ring. There is some enhancement of free radical molecular cations due to the corresponding formation of neutral polyynes. Fragment anions are also produced with a strong preference for very H-deficient carbon clusters, in some cases being the same as carbon cluster anions observed in space. Comparisons of PAH TOF-SIMS spectra with those of asphaltenes are discussed in detail.

Annealing induced carrier activation and PL enhancement in Ge-on-Si grown by low temperature MBE

A series of phosphorus-doped Ge-on-Si were grown by molecular beam epitaxy and then annealed at different temperatures to investigate dopant activation and diffusion. The X-ray diffraction and reciprocal space mapping results show that an in-plane tensile strain up to 0.26% was introduced by annealing. Hall effect measurement results revealed that annealing can effectively activate the dopants, and 700 °C is an optimized annealing temperature. High mobility of 300–1000 cm2/V·s for n-type Ge is achieved at room temperature. Secondary ion mass spectrum profile shows that the diffusion coefficient for these P-doped Ge samples is on the order of 10-14 cm2/s after annealing at 700 °C. Significant photoluminescence enhancement in the samples annealed at 700 °C was observed and is attributed to the crystalline quality improvement, residual tensile strain and n+ doping.

TOF-SIMS for carbon hybridization state analysis

Time-of-flight secondary ion mass spectra measured for different carbon allotropes under Bi3+ cluster ion bombardment were acquired. Ion yield of homogeneous (Cn)- and heterogeneous metal-carbon (CsCn)- secondary cluster ions was examined. Qualitative explanation of the regularities was given based on the concept of nonlinear atomic collision cascades. It was suggested that the features of secondary cluster yield can be used for determination of hybridization state of the target material. Unlike most other techniques, secondary ion mass spectrometry is capable of the sputter depth profiling of the hybridization state.

Characterization of Calcium Phosphate Spherical Particles in the Subretinal Pigment Epithelium–Basal Lamina Space in Aged Human Eyes

PurposeMicrometer-sized spherules formed of hydroxyapatite or whitlockite were identified within extracellular deposits that accumulate in the space between the basal lamina (BL) of retinal pigment epithelium (RPE) and the inner collagenous layer of Bruch’s membrane (sub-RPE–BL space). This investigation aimed to characterize the morphologic features, structure, and distribution of these spherules in aged human eyes with and without clinical indications of age-related macular degeneration (AMD).DesignExperimental study.ParticipantsFive human eyes with varying degrees of sub-RPE–BL deposits were obtained from the University College London Institute of Ophthalmology and Moorfield’s Eye Hospital Tissue Repository or the Advancing Sight Network. Two eyes were reported as having clinical indications of AMD (age, 76–87 years), whereas 3 were considered healthy (age, 69–91 years).MethodsCadaveric eyes with sub-RPE–BL deposits were embedded in paraffin wax and sectioned to a thickness of 4-10 μm. Spherules were identified and characterized using high-resolution scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy, and time-of-flight secondary ion mass spectroscopy.Main Outcome MeasuresHigh-resolution scanning electron micrographs of spherules, the size-frequency distribution of spherules including average diameter, and the distribution of particles across the central-peripheral axis. Elemental maps and time-of-flight secondary ion mass spectra also were obtained.ResultsThe precipitation of spherules is ubiquitous across the central, mid-peripheral, and far-peripheral axis in aged human eyes. No significant difference was found in the frequency of spherules along this axis. However, statistical analysis indicated that spherules exhibited significantly different sizes in these regions. In-depth analysis revealed that spherules in the sub-RPE–BL space of eyes with clinical signs of AMD were significantly larger (median diameter, 1.64 μm) than those in healthy aged eyes (median diameter, 1.16 μm). Finally, spherules showed great variation in surface topography and internal structure.ConclusionsThe precipitation of spherules in the sub-RPE–BL space is ubiquitous across the central–peripheral axis in aged human eyes. However, a marked difference exists in the size and frequency of spherules in eyes with clinical signs of AMD compared to those without, suggesting that the size and frequency of spherules may be associated with AMD.

Interaction of Small Hydrocarbons with Fusion Relevant Beryllium Thin Films

Ion-surface collision studies are carried out with small deuterated hydrocarbon cations i.e. CDx + with x = 2-4 colliding with fusion relevant Beryllium (Be) thin films with ions incident energy as low as 0 eV and as high as Ein = 100 eV. Be films are coated on stainless steel surface by the technique of Thermionic Vacuum Arc (TVA); a novel thin film deposition method with primary as well distinguished characteristic of control of ion flux and respective dose towards the substrate. Prior to scattering, methane-d4 99 atom % D is ionized by electron impact and ions are mass and energy analyzed. Ionization and collisions are performed in ultra high vacuum conditions. In these kinds of collision experiments, we have recorded secondary ion mass spectra and plotted respective incident energy resolved abundances of secondary product ions. Relative abundances in percentage of total secondary ions are plotted and it is observed that such beryllium films can accumulate charged hydrocarbon layers as surface adsorbates. These self assembled layers play a primary role in surface-scattering of primary ions. Moreover, it is seen that bond dissociation energy in lighter hydrocarbons is higher than that for heavier species and shows primarily that the deuterium atoms are loosely bounded to carbon atoms in heavier hydrocarbons than in lighter ones.

Characterization of drug-related impurities using UPLC-QTrap-MS/MS in three scan modes: Application to daptomycin

A new non-targeted screening strategy was developed for the detection and relative quantification of known and potentially unknown drug-related impurities in the active pharmaceutical ingredient daptomycin using ultra-high performance liquid chromatography, coupled with hybrid triple quadrupole-linear ion trap electrospray ionization mass spectrometry in three different modes. The precursor ion scan mode was first applied using the m/z transitions of 159.2, 313.2, and 341.2 for rapid screening of all daptomycin-related impurities. Precursor ions detected at specific retention times were selected, fragmented, and focused in enhanced product ion scan mode to obtain secondary ion mass spectra and identify drug-related impurities. Finally, each potential compound was relatively quantified in multiple reaction monitoring mode. Repeatability experiments suggest that this impurity profiling method is a reliable strategy for identifying unknown impurities in daptomycin and other drugs.

Effects of organic additives on the impurity and grain structure of electrodeposited cobalt

Co films were electrodeposited with different additives including dimethylglyoxime, sodium chloride, and mercapto-propanesulfonate (MPS). A systematic study was conducted using scanning electron microscope, four-point probe, secondary ion mass spectrum, and X-ray diffraction to understand the effects of such additives on the morphology, resistivity, impurity incorporation, and grain structure of film, as well as how thermal annealing influences these attributes. The addition of MPS into the electrolyte was found to significantly increase the S incorporation level and decrease the grain size, both contributing to a higher sheet resistance of film. Transmission electron microscope with energy dispersive X-ray spectroscopy and local electrode atom probe tomography were used to determine the distribution of different impurity elements. A pronounced grain structure change from columnar grains to pseudo-spherical grains was observed upon the addition of MPS in electrolyte or the incorporation of S in film. In addition to the precipitation of sporadic S-rich clusters, S and C were also found to segregate at the grain boundaries in annealed Co films, both of which are believed to correlate to the grain growth and a significant resistance drop upon annealing.

Observation of light and secondary ion emissions from surfaces irradiated with highly charged ions

Visible light and secondary ions emitted from various sample surfaces (Si, HOPG, Cu, and Teflon) were observed after irradiation with highly charged ions (HCIs). HCIs were produced using an electron beam ion source (Kobe EBIS) at Kobe University. Visible emissions were detected using a liquid nitrogen cooled CCD detector. The mass spectrum of secondary ions was obtained using a quadrupole mass analyzer. The major constituent in both light and secondary ion emissions was hydrogen. Balmer lines were the dominant form of light emission as observed from spectra, and proton signals were the most intense peaks in SIMS spectra. The emission intensity of Balmer light and the proton signal intensity (as observed from the SIMS spectrum) both increased as the charge state of the incident HCI increased. Both intensities were roughly proportional to the third to fourth power of the charge state. Spatial distribution of Balmer light was measured and the kinetic energy of hydrogen sputtered from the surface was estimated to be ∼20 eV. The SIMS measurement results for the Teflon sample demonstrate the advantage of using SIMS with an HCI probe for detecting electronegative elements.

Анализ углеродсодержащих материалов методом вторично-ионной масс-спектрометрии: содержание атомов углерода в sp-=SUP=-2-=/SUP=-- и sp-=SUP=-3-=/SUP=--гибридных состояниях

A new approach to the analysis of carbon-containing materials by the method of secondary ion mass spectrometry is studied, which allows one to determine the concentration of carbon atoms in the states of sp2 and sp3 hybridization. It is proposed to use the ratio of the intensities of cluster secondary ions C8/C7 as the main parameter of the mass spectra of secondary ions characterizing the concentration of N(sp3). From measurements of several test structures, a calibration dependence of N (sp3) on the C8/C7 ratio was obtained. The N(sp3) profiles of diamond-like carbon samples grown on diamond and silicon substrates were measured, showing an N(sp3) concentration of 0.3 to 0.6 for different growth modes and an inhomogeneous distribution of the N(sp3) concentration over the thickness of the samples.

Development of an Argon Gas Cluster Ion Beam for ToF‐SIMS Analysis

Argon gas cluster ion beams (Ar‐GCIBs) are widely used as a sputter and primary beam for analyzing soft materials such as organic and biological samples in secondary ion mass spectrometry. We designed a novel ionization source using Simion simulation to improve the beam generation efficiency, and compared with the experimental results. Simulation results of different operation voltages, which are acceleration and extraction from the ionization source were in good agreement with the experimental results. At Ar pressure of 25 bar, total ion beam currents from the ionization source reached 80 μA. The highest current of cluster in the ion beam was found at cluster sizes of 1400. Simple linear time‐of‐flight mass spectrometer was constructed and then a secondary ion mass spectrum signal of Rhodamine 6G was obtained by using a Ar1400+ (@10 keV) cluster ion beam.

Experimental Observation of the Confinement of Atomic Collision Cascades during Ion Sputtering of Porous Silicon

Results of investigation of the mass spectra of secondary ions sputtered from bulk (continuous) and porous silicon targets with various characteristic core particle dimensions are presented. It has been established that the sputtering of nanostructured Si samples leads to a significant increase in the relative yield of massive cluster ions. This effect is especially pronounced when the characteristic nanoparticle size approaches the range of bombarding ions in the Si target. The obtained results are explained taking into account the confinement of atomic collision cascades.

Экспериментальное наблюдение эффекта ограничения каскада столкновений при распылении пористого кремния

AbstractResults of investigation of the mass spectra of secondary ions sputtered from bulk (continuous) and porous silicon targets with various characteristic core particle dimensions are presented. It has been established that the sputtering of nanostructured Si samples leads to a significant increase in the relative yield of massive cluster ions. This effect is especially pronounced when the characteristic nanoparticle size approaches the range of bombarding ions in the Si target. The obtained results are explained taking into account the confinement of atomic collision cascades.

Gas cooling secondary ions emitted by gas cluster ion beam at the travelling-wave ion guide of a Q-ToF-SIMS system

The work was aimed at using gas to cool the secondary ions emitted from gas cluster ion beam (GCIB) bombardment of biosamples for lowering the ion energy distribution and thus enhancing the detection sensitivity for secondary ion mass spectrometry (SIMS). An Ar-cluster ion source at energy in an order of keV was installed with the Q-ToF (Quadrupole Time-of-Flight) premier at the Quantum Science and Engineering Center, Kyoto University. The main component of the Q-ToF premier consisted of a travelling-wave ion guide, a mass filter quadrupole lens, a travelling-wave collision cell, and a ToF analyzer. A 1,2-Distearoyl-sn-glycero-3-phosphocholine (DSPC) sample was used in the study on cooling the secondary ions at the travelling-wave ion guide by using helium and molecular nitrogen gas. The DSPC sample was impinged with primary Ar-cluster ions at energy 10 keV and sputtered for secondary ions in an energy range from zero to several hundred eV. Sputtering-emitted secondary ions were extracted to the Q-ToF mass spectrometer. The experiment was carried out to measure DSPC secondary ion mass spectra in two modes at varied pressures of helium or molecular nitrogen gas. The first mode was the MS mode and the other was the MS/MS mode which defined the m/z = 790.6 Da for the protonated molecule at the mass filter quadrupole lens. The experiment found that the secondary ion yields (SIYs) in the MS mode reached the maximum at 2.0 and 0.35 Pa for helium and molecular nitrogen, respectively. In the MS/MS mode, the SIYs reached the maximum at 2.5 and 0.35 Pa for helium and molecular nitrogen, respectively, and however, some fragments could not be eliminated by the cooling molecular nitrogen gas. The cooling of the secondary ions for lowering the energy distribution and the transverse direction of the secondary ions by using helium was more effective and stable than by using molecular nitrogen.

Secondary ion formation on indium under nuclear and electronic sputtering conditions

The electronic sputtering of indium under swift heavy ion bombardment is investigated using time of flight secondary ion mass spectrometry in combination with 157 nm laser postionization. Secondary ion and neutral mass spectra generated under the impact of 4.8 MeV/u 48Ca10+ ions are analyzed in order to determine the ionization probability of the emitted indium atoms, and the results are compared to those measured under nuclear sputtering conditions via bombardment by 5 keV Ar+ primary ions. The influence of surface contamination on the ionization probability is studied by comparing (1) a pristine surface covered by a native oxide layer, (2) a kilo-electron-volt sputter-cleaned surface, and (3) a controlled oxygen coverage established by dosing the precleaned surface with O2. It is found that the native oxide layer increases the ionization probability for both kilo-electron-volt and mega-electron-volt primary ions. In contrast, oxygen deposited on a sputter-cleaned surface results in the well-known matrix effect for kilo-electron-volt ions, but has no influence on the ionization probability for the mega-electron-volt ions. In the case of a thoroughly sputter-cleaned surface a four- to sevenfold higher ionization probability for indium atoms is found for 4.8 MeV/u 48Ca10+ as compared to 5 keV Ar+ bombardment.

Time-of-flight secondary ion mass spectrometry using a new primary ion beam generated by vacuum electrospray of a protic ionic liquid, propylammonium nitrate.

Protic ionic liquids have the potential to be useful materials for primary ion beams in terms of protonation, since they have active protons. Selecting protic ionic liquids suitable for primary ion beams is of great importance to increase molecular secondary ion yields. Propylammonium nitrate ([C3 H7 NH3 ][NO3 ]) seems promising in view of its proton affinity. It is likely that [C3 H7 NH3 ]+ cations can act as proton donors, and [NO3 ]- anions can work as proton acceptors. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiments have been performed to verify the usefulness of [C3 H7 NH3 ][NO3 ]. A primary propylammonium nitrate cluster ion beam was generated by vacuum electrospray, and then used to analyze amino acids (arginine, glutamic acid, aspartic acid), angiotensin II and polyethylene glycol. Positive and negative secondary ion mass spectra were obtained to study both protonation and deprotonation. The propylammonium nitrate cluster ion beam successfully generated protonated molecules [M+H]+ of all the analytes in positive ion mode. The primary ion beam also generated deprotonated molecules [M-H]- of glutamic acid, aspartic acid and angiotensin II in negative ion mode. Additionally, adduct ions related to [C3 H7 NH3 ][NO3 ] were detected in the case of arginine and polyethylene glycol. The TOF-SIMS experiments confirmed that the propylammonium nitrate cluster ion beam was useful in generating molecular secondary ions, demonstrating that it is well suited for a primary ion beam in TOF-SIMS.

Luminescence of Donor-acceptor-pair in Fluorescent 4H-SiC Doped with Nitrogen, Boron and Aluminum

Fluorescent 4H-SiC, co-doped with donor and acceptor impurities, can work as phosphor for visible light emission by recombination. Donor concentration and acceptor impurities are two important factors which influence luminescent properties of fluorescent 4H-SiC. In this study, 3 inch N-B-Al co-doped 4H-SiC crystals were prepared by physical vapor transport method. Crystalline type and N-B-Al concentration of the doped 4H-SiC were measured by Raman spectrum and secondary ion mass spectra. Influences of doping concentrations on the photoluminescence were studied by photoluminescence excitation and emission spectra, luminescence decay curves, and internal and external quantum efficiencies. It is found that p-type fluorescent 4H-SiC with low Al doping concentration shows intensive yellow-green fluorescence at room temperature. Heavily doped N and B and lightly doped Al in 4H-SiC produce enough electron hole pairs for the recombination. This sufficient recombination enhances internal quantum efficiency of fluorescent 4H-SiC. Furthermore, the recombination is also helpful to increase their photoluminescence intensity and average fluorescence lifetime.

Relationship between grain boundary diffusion in nanocrystals and amorphous microstructure

The effects of microstructure on diffusion behaviors of Ni in Zr48Cu36Ag8Al8 alloy were investigated by transmission electron microscope and secondary ion mass spectrum. The temperature dependence of Ni diffusivities in Zr48Cu36Ag8Al8 alloy with different states (metallic glass, nanocrystals and coarse crystals) has been measured in the temperature range of 693–723 K. The results show that diffusion behavior is microstructure dependence, and the relations between the microstructure and diffusion are discussed. The activity energy of the grain boundary diffusion in nanocrystals calculated by the Suzuoka solution is about 1.433 eV/atom. It is equivalent with that of metallic glass, which is attributed to the similar microstructure between the two. Copyright © 2016 John Wiley & Sons, Ltd.

Comparative study on beryllium and magnesium as a co-doping element for ZnO:N**Project supported by the National Key Basic Research Program of China (Grant No. 2011CB302000), the National Natural Science Foundation of China (Grant Nos. 51232009 and 51202299), the Fundamental Research Funds for the Central Universities, China (Grant No. 11lgpy16), the Natural Science Foundation for Jiangsu Provincial Higher Education, Institutions of

Stable nitrogen doping is an important issue in p-type ZnO research for device applications. In this paper, beryllium and magnesium are systematically compared as a dopant in ZnO to reveal their nitrogen-stabilizing ability. Secondary ion mass spectrum shows that Be and Mg can both enhance the stability of nitrogen in ZnO while Be has a better performance. Zn 2p and O 1s electron binding energies change in both MgZnO and BeZnO thin films. Donor-acceptor luminescence is observed in the BeZnO samples. We conclude that Be is a better co-doping element than Mg for p-type ZnO:N.