Masao Inoue

Improvement of the electric field in the cylindrical trapped-ion cell

Abstract This paper reports improvement of the electric field in the cylindrical Fourier transform ion cyclotron resonance (FT-ICR) trapped-ion cell. We have designed a cell in which the trapping plates of the conventional cell are replaced by three pairs of electrodes with circular apertures of different radii and the potential applied to each pair of electrodes is independently controlled. Theoretical analysis of the electric fields in both the conventional and improved cells has been made. Experimental results on the drift motion of ions due to the inhomogeneity of electric field are presented. Comparison between the conventional and the improved cell demonstrates a significant increase in the uniformity of the electric field. Enhancement of the signal intensity and resolution in the FT-ICR spectrum is observed.

Evolution of an ion cloud in a Fourier transform ion cyclotron resonance mass spectrometer during signal detection: its influence on spectral line shape and position

Abstract The factors responsible for temporal variation of the detected frequency in an FT ion cyclotron resonance (ICR) spectrometer are analysed. The time-dependent frequency behaviour is believed to be caused by a change in ion cloud configuration, the number of detected ions, and the ion cloud position in the electric field of the ICR cell. The spectral peak shape is calculated for an ensemble of non-interacting ions distributed over amplitudes of axial oscillations. The influence of the Coulomb interaction on the signal and the spectral peak shape is studied by a computer simulation using a highly parallel computer.

XPS study of H-terminated silicon surface under inert gas and UHV annealing

We have investigated the changes of chemical bonding states of an H-terminated silicon surface under inert gas (Ar,N 2 ) and ultrahigh vacuum (UHV) annealing using X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). SiC is formed (corresponding to ∼0.1 monolayer) under inert gas and UHV annealing at around 500°C, which is coincident with the temperature of the dangling bonds formation at the silicon surface by hydrogen desorption, whereas SiC is not formed under O 2 annealing. From the precise analysis using a combination of XPS and TDS, the SiC formation is related to the reaction between the silicon surface and the organic contamination that is unavoidably adsorbed during air exposure. We also studied the electrical properties of metal oxide semiconductor capacitors with a chemical vapor deposited silicon oxide gate insulator formed on Ar- and O 2 -annealed silicon surfaces. Ar preannealing increases the leakage current by approximately 10 - 4 times compared with O 2 annealing.

High-precision determination of osmium and rhenium isotope ratios by in situ oxygen isotope ratio correction using negative thermal ionization mass spectrometry

Abstract The Os and Re isotope ratios were determined from the measurements of OsO3 and ReO4− ions by negative thermal ionization mass spectrometry. It was found that the oxygen isotope ratios of OsO3− and ReO4 ions vary to a large extent by the fluctuations in oxygen pressure in the ion source of the mass spectrometer and that the stability of oxygen pressure and the in situ correction for the interference of Os16O217O−, Os16O218O− and Re16O318O− ions are indispensable to the high-precision determination of Os and Re isotope ratios. The precision of 184 Os/188Os ratio is further improved to about 0.1% in relative standard deviation if the interference of the 192PtO2− ion with the 184Os/3− ion was taken into account. The 187 Re/185Re ratio was determined as 1.67389 ± 0.00014 and the corresponding calculated atomic weight of Re is 186.206747 ± 0.000019, which is much more precise than the preciously reported values.

Effect of frequency sweep direction on motion of excited ions in fourier transform ion cyclotron resonance cells.

Ion motion during frequency sweep excitation was computer simulated to study the effect of the direction of frequency swee on the z motion of ions in a cylindrical Fourier transform ion cyclotron resonance (T-ICR) cell. It is shown that the z motion is more forcefully excited by upsweep than by downsweep; thus at large amplitudes ions are more easily ejected to the trapping electrodes by upsweep and larger cyclotron orbits can be achieved by downsweep. This effect was confirmed by experiment and the results are favorably compared with the calculations. From these results it is concluded that downward sweeping is advantageous for ion detection and upward sweeping is preferable for ion ejection. The simulations clearly explain the effect of the direction of frequency sweep by visualizing the directions of the forces that ions experience immediately after the excitation of their cyclotron motion. It was demonstrated by experiment that the z ejection can be reduced by applying a phase-adjusted ac potential to the trapping electrodes.(847-852)

Collective motion of ions in an ion trap for Fourier transform ion cyclotron resonance mass spectrometry

When two kinds of ions with a very small mass difference are trapped at high density in the Fourier transform ion cyclotron resonance (FT-ICR) cell and are coherently rotating in their cyclotron orbits, collective motion of two ion packets takes place due to the Coulomb interaction and only one peak appears in the spectrum rather than two peaks at their own mass-to-charge ratios. The phenomenon is theoretically studied with a model of two charged particles orbiting in a plane perpendicular to a uniform magnetic field. This model shows that, while the center-of-mass is rotating in a circular orbit at a frequency corresponding to the weighted average of the two cyclotron resonance frequencies, the two particles are rotating around the center-of-mass with an oscillating radius. The potential between the two particles is calculated and the resonance condition which decouples the coupling motion is derived as a function of mass, number of charges, the orbital radius of the center-of-mass and the magnetic field strength. The condition is experimentally examined with CO+ (m/z = 27.9949) and C2H4+ (m/z = 28.0313) ions, varying the number of charges and the cyclotron radius, and an agreement with the theory is found. The collective motion of highly multiply charged heavy ions produced from biomolecules is also discussed.

Diffusion Control Techniques for TiN Stacked Metal Gate Electrodes for p-Type Metal Insulator Semiconductor Field Effect Transistors

We have investigated a polycrystalline silicon (poly-Si)/chemical vapor deposited titanium nitride (CVD-TiN) stacked structure as a metal gate with a high-k for p-type metal insulator semiconductor field effect transistors (p-MISFETs). A divided-CVD method provided an appropriate effective work function (4.9–5.2 eV) on HfSiON for p-MISFETs. However, the deposition of poly-Si on CVD-TiN films shifted the effective work function to a midgap (~4.6 eV), and Ti, Hf, and Si diffused into poly-Si/CVD-TiN/high-k structures during poly-Si deposition. Then, we found that an increase in the deposition temperature of CVD-TiN films and the insertion of a physical vapor deposited (PVD)-TiN film between the poly-Si and CVD-TiN layers are effective in suppressing these diffusions. In particular, the insertion of the PVD-TiN film provided an appropriate effective work function of 4.9 eV. Therefore, we found that the diffusion control techniques for poly-Si/TiN/high-k stacked structures are highly effective for obtaining the appropriate work function for p-MISFETs.

Capture Cross Section of Electric-Stress-Induced Interface States in (100) Si Metal/Oxide/Semiconductor Capacitors

The capture cross section of interface states induced by Fowler-Nordheim tunneling electron injection in (100) n- and p-Si metal/oxide/semiconductor (MOS) capacitors has been measured as a function of interface-state density by means of the ac conductance method. In n-Si MOS capacitors two interface states are generated in the upper half of the Si gap, while in p-Si MOS capacitors only one interface state is observed in the lower half of the gap. The capture cross section for electrons (upper half of the gap) and for holes (lower half of the gap) tends to decrease when the interface-state densities exceed about 1.5×1011 cm-2eV-1. This behavior is explained by taking the occurrence of additional tunneling to defect states in the oxide into account. Moreover, the difference in the slopes of the descending characteristics of electron and hole capture cross sections is used to estimate the effective-mass ratio of an electron and a hole in the SiO2 gap.

A New Concept of Isotope Separation Using Ion Cyclotron Resonance in a Magnetic Field Having a Radial Component

A new method of isotope separation is proposed. Isotopes are ionized in a magnetic field in a solenoid and are confined axially in an electrostatic potential well. Ions moving in a cyclotron orbit undergo a force which is perpendicular to both the radial magnetic field component and the velocity. Because axial oscillation takes place over the region where the component changes its direction, two isotopes can be separated in opposite directions by accelerating one of the isotopes at one extreme of the oscillation and the other at the other extreme. The axial motion of ions is assumed to be in phase (phase-locked). To experimentally confirm the effect of the radial component on ion motion, we moved the center of oscillation along the axis of the solenoid from its center to a position where both the axial and radial components vary with the coordinates, and we excited the cyclotron motion of ions. From the measured shift in the signal frequency of the accelerated ions, we could estimate the amount of displacement of the center of the cyclotron orbit as a function of the velocity of the accelerated ions. The condition for separation is studied by solving the equation for ion motion with two different magnetic field distributions. Computer simulation of the ion trajectory is carried out to demonstrate the feasibility of the method.

New Interpolation Formulas for Apodized, Magnitude-Mode Fourier Transformed Spectra:

Interpolation techniques for the magnitude-mode discrete Fourier transformed (DFT) spectra of exponentially damped sinusoids have been developed. However, simple formulas to interpolate the apodized DFT spectra have not been given, except those used to interpolate the Hanning-apodized spectra. In this paper, we derive simple interpolation formulas using the sine-bell and rectangle windows. It is found that the formulas for the rectangle window are essentially identical to Lorentzian interpolation. Furthermore, we derive generalized formulas to interpolate DFT spectra apodized by a family of sin α (X) windows, which includes the rectangle, sine-bell, and Hanning windows. We call the proposed interpolation “generalized” because any integer value of α can be used. Simulation results show that the accuracy of interpolation is improved remarkably with increases in the value of the parameter α.