Ion Source Chamber Research Articles

Precise determination of Sm, Nd concentrations and Nd isotopic compositions at the nanogram level in geological samples by thermal ionization mass spectrometry

In this paper, a high sensitivity method for measurements of Nd isotopes as NdO+, on a TIMS using a single W filament with TaF5 as an ion emitter is presented. Although analyzing Nd isotopes as oxides (NdO+) is a well known technique, this is the first report to analyze Nd isotopic compositions as oxides using W filaments and the TaF5 emitter. When 0.5–1 ng loads of a Neodymium isotopic reference reagent, JNdi-1, were measured using this method, the ion yields were found to be mostly in excess of 15% and could be as high as 32%. Internal precision on 143Nd/144Nd could be better than 10 ppm (2SE) for 1 ng JNdi-1 loads and better than 15 ppm (2SE) for 0.5 ng JNdi-1 loads; thirteen replicates of 0.5–1 ng JNdi-1 loads yielded a 143Nd/144Nd value of 0.512112 ± 0.000028 (2SD). Compared with the previously reported NdO+ measurement method using the Re (or W) filaments + Silica-gel + H3PO4 loading techniques, this method has advantages including higher sensitivity, a more stable ion beam, and no need for oxygen gas to be bled into the ion source chamber. Sm isotopes were analyzed as Sm+ using the W filaments and the TaF5 emitter, and high sensitivity and good ion beam stability were also obtained. Several international rock reference materials, including an ultramafic rock reference material USGS PCC-1 that contains very low amounts of Sm and Nd, were analyzed with full column chemistry and the TaF5 method, and the results of Sm, Nd concentrations and Nd isotopic data are in good agreement with the reported values. Combined with a highly efficient and low-blank column chemistry to separate Nd from Sm, Ce, and Pr, this method holds potential to analyze Sm, Nd concentrations and Nd isotopic compositions of highly depleted peridotites; very small aliquots of minerals such as garnets; extra-terrestrial materials of limited sample size; and environmental samples that contain very low quantities of Sm and Nd.

Development of low energy ion beam system for space charge compensation experiments

A low energy ion beam system for space charge compensation (SCC) experiments was developed and evaluated. This system was designed for observation of SCC of a positive ion beam with an electron beam. The system consisted of the ion source chamber and the SCC experiment chamber. The ion source chamber was equipped with the compact microwave ion source for low voltage extraction. Ion current at initial position of the analysis chamber was 84 microA at extraction voltage of 500 V, and satisfied a condition to observe the SCC effect clearly. In order to evaluate the SCC, we measured the arrival ion current by supplying thermionic electrons, which were extracted from a tungsten filament driven by ac voltage. As the electron supply, the arrival ion current increased from 40 to 68 microA at the potential of filament of +3 eV which produced the thermionic electron with extremely low energy extracted by space charge of the ion beam.

On‐plate digestion of proteins using novel trypsin‐immobilized magnetic nanospheres for MALDI‐TOF‐MS analysis

In this study, a novel method of on-plate digestion using trypsin-immobilized magnetic nanospheres was developed followed by MALDI-TOF-MS for rapid and effective analysis and identification of proteins. We utilized a facile one-pot method for the direct preparation of amine-functionalized magnetic nanospheres with highly magnetic properties and the amino groups on the outer surface. Through the reaction of the aldehyde groups with amine groups, trypsin was simply and stably immobilized onto the magnetic nanospheres. The obtained trypsin-linked magnetic nanospheres were then applied for on-plate digestion of sample proteins (myoglobin and Cytochrome c). Moreover, after digestion, the trypsin-linked nanospheres could be easily removed from the plate due to their magnetic property, which would avoid causing contamination on the ion source chamber in MS. The effects of the temperature and incubation time on the digestion efficiency were characterized. Within only 5 min, proteins could be efficiently digested with the peptide sequence coverage higher than or equal to that of the traditional in-solution digestion for 12 h. Furthermore, RPLC fractions of rat liver extract were also successfully processed using this novel method. These results suggested that our improved on-plate digestion protocol for MALDI-MS may find further application in automated analysis of large sets of proteins.

Production of high-flux mixed ion beam for study of plasma material interaction

A steady-state and high-flux ion beam irradiation test device (HiFIT) equipped with an ECR ion source and spherical electrodes was developed. Hydrogen irradiation fluxes were 3.6×10 21 Hm −2 s −1 for an acceleration voltage V acc of 3 kV and about 4×10 20 Hm −2 s −1 for V acc from 0.15 to 0.5 kV (dominant ion species is H 3 +). Mixed ion beams with hydrogen and carbon with the carbon concentration from 0.1% to ∼10% were obtained. Carbon impurity concentration was controlled by puffing methane gas or putting graphite plates in the ion source chamber. Carbon impurity concentration was calculated by using measured effective cross-sections (including dissociation and neutralization) of molecular ions in a beam transport chamber. New mixed material effect on blister formation of tungsten bombarded with hydrogen and carbon mixed ion beam was observed. It was found that carbon impurity of less than 1% in hydrogen beams significantly affected blister formation.

RF ion source for low energy ion implantation — beam profile control of a large-area ion source using 500-MHz discharge

In order to fabricate ULSI devices on large wafers up to 300 mm in diameter, an ion implantation system that can transport a high-current ion beam with low energy and suppress the charge-up on the wafer is necessary. Both problems come from the space charge effect; to solve them it is convenient to use a large-area ribbon-beam ion source, because it leads a low current density and low charge-up on the wafer. However, handling of the large-area beam is not easy and beam profile control on the wafer is even more difficult. This article is concerned with a method for controlling the beam profile of the large-area ribbon-beam ion source in RF plasma production. As the size of the ion-source chamber is comparable to the RF wavelength, then the ion-beam profile can be controlled by adjusting the size of the variable windows into the chamber for the RF wave. Accordingly, less than 2% spread in uniformity of the large-area ion beam is achieved.

Measurement of isotopes of light rare earth elements in the form of oxide ions: a new development in thermal ionization mass spectrometry

An isobaric interference free thermal ionization mass spectrometry (TIMS) method is presented here for the precise isotope measurements of light rare earth elements (LREEs). LREE isotopes can be measured in the form of monoxide ion (MO+), but the previous determinations of LREE isotopes in the form of oxide were hindered, notably by the 17O and 18O related isobaric interferences. In the present study, 16O-enriched oxygen was introduced into the ion source chamber via a specially designed gas inlet system. It was observed that the isobaric interferences caused by 17O and 18O were remarkably reduced by up to 6 and 70 times, respectively, compared to those caused by natural oxygen bleeding. Isotopic ratios of La, Ce, and Nd obtained without isobaric interference corrections show the excellent precision and accuracy in the present study. The results also shed some light on the formation mechanism of the measured oxide species in TIMS. Furthermore it promises more precise determination of LREE abundances and La-Ce and Sm-Nd ages in geochemistry and cosmochemistry.

Design and Optimization of a Corona Discharge Ion Source for Supercritical Fluid Chromatography Time-of-Flight Mass Spectrometry

The interfacing of capillary column supercritical fluid chromatography (SFC) to time-of-flight mass spectrometry (TOFMS) through atmospheric pressure chemical ionization (APCI) was investigated. An ion source chamber and a new, flexible, and efficient transfer line from the SFC to the TOFMS system were designed to accommodate the requirements of this study. Ionization of analytes was performed using a corona discharge needle. The interface was equipped with two multiple-axis translation stages for positioning of the transfer line tip and the discharge needle inside the ion chamber. The investigations were oriented toward the optimization of parameters which have a strong effect on the intensity and stability of the analyte signal, including background stability, corona discharge needle positioning in the ion source, transfer line tip and discharge needle relative positioning, curtain gas and makeup gas flow interactions, ion chamber temperature, and elution pressure of analytes from the SFC system.

A low voltage ion transport system for external ionization fourier transform mass spectrometry

An efficient ion transport system that interfaces external ion sources with a commercial dual-cell Fourier transform mass spectrometry (FTMS) system so as to retain maximum experimental flexibility has been constructed. Electrostatic lenses were used for ion transfer with potentials less than 200 V to preclude discharges. Spectra were recorded by thermal ionization and by electrospray ionization. Other high pressure ionization methods can be easily added to the external ion source chamber, making this a general solution for ion transport into an FTMS system. The efficiency of ion transfer was measured to be approximately 30%. A pressure ratio of 10 5 between the external ion source chamber and the second cell has been demonstrated. The system incorporates a computer-controlled gate valve to isolate the cell regions from the external ion source chamber, permitting optimal conditions for ion injection and accumulation, and then after closing the valve, recording spectra at low pressure with high resolution. Spectra of Gramicidin S (resolution 90,000 at m/z 1164), aprotinin (resolution 410,000 at m/z 1304), and horse heart cytochrome c (resolution 50,000 at m/z 1546) are shown.

Adaptation of a glow discharge mass spectrometer in a glove-box for the analysis of nuclear materials

A VG9000 glow discharge mass spectrometer has been modified for the direct analysis of solid nuclear samples within a glove-box environment. Because containment is needed for the analysis of this kind of material, the glove-box encloses all parts of the instrument that come into contact with the sample, namely the ion source chamber, sample interlock and associated pumping system. External modifications eliminate outside contamination by the fitting of absolute filters on all source supplies. Internally, the design of the ion source has been altered to minimize the number of operations performed inside the glove-box thereby simplifing operation and routine maintenance. These modifications retain the ion extraction and focusing properties of the instrument. The data presented show that there is no compromise in the analytical performance of the instrument when placed in the glove-box. Data representative of nuclear materials is also shown.

Design and performance of a novel electrospray interface

In this work a new electrospray system has been developed which employs heat as a means of desolvation and requires no counterflow of heated gas. This article describes the operation and performance of this device, with particular emphasis on the differences between it and those described earlier. Results are presented that illustrate the dependence of signal intensity on ion source and spray chamber temperatures and on the composition and flow rate of mobile phase into the electrospray. Results on proteins electrosprayed from aqueous solutions are presented including a bacterial protease which has a tight tertiary structure. The ability to obtain fragmentation data by collisionally induced dissociation in the interface is also discussed.

Fundamentals of ion-beam-assisted deposition. I. Model of process and reproducibility of film composition

An ion-beam-assisted-deposition (IBAD) system is under development to fabricate Si1−x Nx films for optical devices. Reproducible film composition requires characterization of the relationship between the incorporated nitrogen atom fraction x and the real time experimental measurable quantities. In this paper a simple model is presented which relates the film composition x to the measured beam current density JF , the vapor impingement rate Q, and the chamber pressure p. Effects included in the model are reflection of energetic particles, sputtering from the film surface, and charge exchange neutralization of the ions. Each term in the model is examined as a potential source of both systematic and random deviations of the data from the model. Data on film composition as a function of the nitrogen ion current to deposition rate ratio are presented for several sets of ion source voltages and chamber pressures. It is shown that by modifying the deposition system so as to minimize the identified sources of error, variation in composition can be reduced below 3 at. % nitrogen. Both the model and the discussion of the experimental sources of error are applicable to other IBAD systems.

Analysis of model polyurethane thermolysis products by direct mass spectrometer sampling

AbstractThe results obtained using a molecular beam direct sampling mass spectrometer system to determine the thermolysis products and investigate the decomposition kinetics of two model linear polyurethanes are reported. The polyurethanes are shown to degrade in this system strictly to the polycondensation reactants. These results conflict with previous research which indicated that the model polymers degraded by different mechanisms and yielded different degradation products. Kinetic analysis of results obtained from rapid thermolysis of the polymer in the ion source chamber of the pyrolysis mass spectrometer using the activation energy and frequency factor parameters deduced from thermogravimetric analysis of the same polymers reproduced the experimental data on decomposition as a function of time and temperature quite satisfactorily.

Low‐Energy Contaminant in B++ Implantation and Its Elimination

The problem of low‐energy B+ contamination in the implantation of B++ ions using pre‐analysis type ion implanters is examined and the causes of contamination mechanisms are discussed. Experiments were performed on pre‐analysis‐type medium‐current implanters to investigate the effects on B++ beam purity due to the use of solid boron source and liquid boron source in an effort to lower ion source chamber operating pressure, the use of electrostatic ion beam filter to remove low‐energy contaminants from the dissociation of molecules if any, the use of aluminum waveguide liner to reduce gas desorption, and the effects of improved vacuum after cryopump regeneration. Experimental results indicated that, despite all these improvements, uncontaminated B++ implants cannot be assured for either gas or solid source. The secondary electrostatic analysis is demonstrated to be a sensitive technique for setup and monitoring of beam purity of doubly charged ion implants, and essentially uncontaminated B++ implants have been achieved with either gas source or the solid source. This was previously impossible without the refined secondary electrostatic analysis technique.

Ion-beam sputtering apparatus for deposition of multilayered films

Multilayered films are,composed of repeated alternate deposition of ultrathin layers of different materials. These films are of interest for their unique properties not intrisically found in conventional monolithic substances. Multilayered films have been prepared by several methods: molecular beam epitaxy [1], thermal evaporation [2, 3], chemical vapour deposition [4], and sputtering [5-7]. In an attempt to deposit thin films of tin oxide, we used an ion-beam sputtering (IBS) apparatus with a simplified accelerator system [8]. The IBS method is particularly attractive for deposition because a high-purity thin film with an improved adhesion to the substrate can be obtained. In the present letter we describe the construction of the IBS apparatus specially designed for the synthesis of multilayered films. The constructed apparatus is simple, relatively inexpensive and convenient to control. The results of analysing periodic structures of Pt/SnOx multilayers deposited by this apparatus are also presented. The outline of the apparatus used to prepare multilayered films is shown in Fig. 1. The vacuum chamber is a vertical cylinder, 40 cm in diameter and 80 cm tall, of which only the upper-half is actually used. The base pressure is below 1 x 10 5 torr. Argon gas of 99.9995% purity is fed into the ionsource chamber and the chamber pressure during the run is maintained at (1 + 0.1) x 10 4torr. The target is placed at about 45 ° to both the axis of the beam and the substrate. The distance from the centre of the target to the ion-source chamber and to the substrate is 3.5 and 5 cm, respectively. The target assembly can contain four different targets and the targets are screwed to the aluminium target-holders of 8-cm diameter. In this experiment two targets, platinum foils and a sintered tin oxide disc, were used. The rotation of the targets was carried out using an ordinary stepping motor (Oriental motor, PH266-01) in the vacuum chamber. Generally the vacuum hinders the rapid heat transfer, thus heat tends to accumulate in the running motor and augments its temperature. To avoid this temperature increase of the stepping motor, the motor is mounted on a water-cooled copper plate; flexible hoses are used to conduct the cooling water. Although the placing of the stepping motor in the vacuum chamber induces a possible contamination from the gaseous species from the organic materials in the motor, it makes the overall design of the apparatus very simple. A microcomputer (NEC, PC-8801) and a driver/controller (Cosmotron, PMC-14C) together with the stepping motor control the rotation of the targets. When the sputtering time to form a layer reaches a preset value, the control system turns the target assembly by 90 ° to the other target. It takes about 1 sec for this rotation. The substrate assembly contains eight different substrate holders that can be selected manually via a d.c. motor. The shutter has a window (2 c m x 4 cm) through which sputtered particles deposite on a designated substrate. During the pre-sputtering of the targets, the window is closed. The substrate-shutter separation is held at 4 mm so that all particles passing through the window hit the planned substrate, thus contamination of other substrates by the sputtered particles is avoided. The electrical connections for the system are shown schematically in Fig. 2. It is similar to that used in our previous experiment [8], however the stability of the discharge current increased markedly by employing a d.c. current supply (Metronix, 411A-32) and an insulation transformer instead of a voltage slider. The electrical system is run typically at a discharge voltage of 50 V, a discharge current of 600 mA, a beam voltage of 1000 V, an accelerator voltage of 150 V and an ionbeam current (defined here as the current between the target and the ground) of 0.8 mA. The temperatures of the substrate and the target reached 90 and 130°C, respectively after 3h; they were measured by a CA-thermocouple during the sputtering of an

Plasma filament ion source for high current implanter

A plasma filament ion source has been developed as a long lifetime ion source for use in ion implanters. In this ion source, a plasma filament replaces a conventional metallic filament used in a Freeman type ion source. This ion source consists of two compartments, i.e. a plasma generator and an ion source chamber interconnected by a tapered narrow duct. The pressure difference between the two parts made by differential pumping prevents the feed gas from flowing into the plasma generator. With any combination of a plasma filament of either argon or neon and a feed gas of either AsF 5 or PF 5, the lifetime was found to be more than 90 h with an extraction voltage of 40 kV and a corresponding ion current density of 20 mA/cm 2; a considerable amount of As + and P + ions were observed in mass spectra. This ion source is eminently suitable for oxygen ion production and useful for realizing a full cryopumping ion implanter system.

Dynamic measurement of ultramicro amounts of gases with an ionization gauge

A nude ionization gauge adjacent to the closed ion-source chamber of a quadrupole mass spectrometer is a sensitive detector of the total amount of gas introduced for dynamic analysis. Linear relations between the amount of gas and the area of the ionization gauge pulse record were found for eight gases. For relatively unreactive gases, linearity extended to the smallest samples that could be detected, approximately 10−10 atm cm3. Validity of the dynamic method of analysis was established by demonstrating that the same response was obtained for pulsed and for continuous sample introductions from calibrated leak sources of each of the eight gases.

Formation of LiHe+ by gas-phase reaction of LiCl with He

LiHe+ was produced in a mixture of LiCl vapour and helium gas using the ion-source chamber of an isotope separator. The appearance energy measured for the LiHe+ ion was 19.3 ± 0.7 eV, which is very close to that for He* (19.8 eV). From this result the mechanism of formation of the LiHe+ ion is deduced as LiCl → He* → LiHe+ + Cl + e−. The cross-section for this reaction was determined to be 2.8 × 10−17 cm2.

Beam source for moderately fast neutral alkali atoms

In certain applications the linear arrangement of ion source and charge exchange chamber in standard charge exchange sources for neutral atomic beams leads to undesirable stray light. To avoid this problem a new design has been developed and tested. The maximum beam flux emerging from this source is 2.0 ⋅ 1010 atoms/s ⋅ mm2 at the energy E = 100 eV. The energy spread ΔE/E ≲0.5%. The angular spread is about 0.47 deg FWHM. Adjusting the ion optics every 100 hours the intensity of the neutral beam has been measured to be stable within 10% over a period of 400 hours.

Modification of an SSMS ion source to reduce residual gas effects

A simple modification to the spark shield of the ion source of a spark source mass spectrograph is discussed. This helps to maintain a low partial pressure of residual gases during sparking of reactive materials. A grid is placed over the viewing slit to prevent energetic neutrals and ions from striking the walls of the source chamber, thereby desorbing unwanted gases into the ion source chamber. The results show a reduction of an order of magnitude in the total pressure during sparking over the conventional spark shield.

Adjustment of the ion energy distribution in double plasma and other synthesized plasma devices

The parallel ion energy distribution of a synthesized plasma can be readily controlled via plasma potential gradients in the ion source chamber(s). Alternatively, layers of electrically biased metal filaments can introduce an isotropic ion heating.