Yukio Fujiwara

Production of Stable Ion Beam of Os3(CO)12 with Compact Metal-Cluster-Complex Ion Source

Metal-cluster-complex ion beams were produced stably using a cluster ion source, which is compact enough to be installed in commonly used secondary ion mass spectrometry (SIMS) systems. As a metal cluster complex, triosmium dodecacarbonyl, Os3(CO)12, was utilized, which has a molecular weight of 906.7. Since precise temperature control is necessary to sublimate the metal cluster complex stably without thermal decomposition, the ion source was equipped with compact heat-removal devices in addition to an external heater. Experimental results showed that the crucible temperature of the metal cluster complex can be maintained at about 130 °C in continuous operation, which is an appropriate temperature for sublimation without the problem of decomposition. The ion source produced steady-state beams of Os3(CO)n+ (n=7 or 8) ions with a beam current exceeding 10 nA at 10 keV. Beam current increased with gas pressure, depending on the temperature of the crucible holding the metal cluster complex. The rate of the change in beam current was within a few percent per hour; hence, in view of stability, the ion source was confirmed as usable in SIMS. Furthermore, beam profile was investigated using a Faraday cup with a knife-edge as well as a GaAs/AlAs multilayer substrate as a beam target.

Secondary Ion Mass Spectrometry of Organic Thin Films Using Metal-Cluster-Complex Ion Source

Tetrairidium dodecacarbonyl, Ir4(CO)12, is a metal cluster complex that has a molecular weight of 1104.9. Using a metal-cluster-complex ion source, secondary ion mass spectrometry (SIMS) of poly(methyl methacrylate) (PMMA) thin films on silicon substrates was performed with a quadrupole mass spectrometer. The secondary ion intensity of PMMA bombarded with Ir4(CO)7+ ions was investigated in the beam energy ranging from 3 to 10 keV at an incident angle of 45°. For comparison, bombardment with oxygen ions, O2+, was also tested. It was confirmed that the use of Ir4(CO)7+ ions enhanced secondary ion intensity by at least one order of magnitude compared with that of O2+ ions. Experimental results also showed that secondary ion intensity increased with beam energy; particularly, high-mass secondary ion intensity markedly increased.

An Oxygen Negative Ion Source of a New Concept Using Solid Oxide Electrolytes

A novel oxygen negative ion source named solid oxide ion source (SOIS) is proposed. To demonstrate its concept, thermionic emission of oxygen negative ions, O - , from a bare surface of yttria-stabilized zirconia (YSZ) was studied with a mass spectrometer capable of detecting negative ions. The emission current was investigated at the temperature range 750 to 950°C under pressures of about 2 x 10 3 to 4 x 10 4 Pa. O ions proved to he emitted into a vacuum from the hare YSZ surface at elevated temperatures. The emission current increased with temperature and applied voltage. From Richardson-Dushman plots, activation energy of the thermionic emission was estimated to be about 2 eV. In continuous operation, the emission current decreased with time, finally approaching zero; however, after intervals, the current recovered. On the basis of the results, a model for explaining the emission mechanism of O ions is proposed. The model is based on three key processes occurring on the surface of electrolytes: (1) formation of O ions on the surface by electron capture of oxygen atoms provided by the migration of oxide ions across electrolytes, (2) accumulation of O ions on the surface, and (3) emission of O ions from the surface.

Component analysis of a mixed beam generated by vacuum electrospray of an ionic liquid

Vacuum electrospray of a quaternary ammonium ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl) amide (DEME-TFSA), was investigated to develop a primary ion source for secondary ion mass spectrometry (SIMS). Since the ionic liquid contains many methyl and ethyl groups as well as protons, its beam is expected to efficiently produce protonated molecules for SIMS analysis of organic materials. Experimental results showed that the beam consisted of charged particles of m/z about 1000 and charged droplets of m/zu2009>u2009105. The current components of both the charged particles and droplets changed with the applied voltage and the flow rate of the ionic liquid. With decreasing flow rate, the current component of the charged droplets increased, whereas that of the charged particles decreased. The m/z values of the charged droplets diminished with decreasing flow rate and increasing capillary voltage. In addition to masses and charge numbers, the numbers of the charged droplets ...

Observation of Sputtered Si Surface Irradiated with Metal Cluster Complex Ions

In this paper, we report the result of surface sputtering of Si using a proto-type compact cluster ion source which has been developed using Os3(CO)12 as a low damage-sputtering source. The surface roughening of Si under the acceleration energy 10 key at incidence angles about 0/spl deg/ and 60/spl deg/ has been studied. The sputtered Si surface was observed by using AFM (atomic force microscope) and SEM (scanning electron microscope).

Secondary-Ion-Mass-Spectrometry Depth Profiling of Ultra-shallow Boron Delta Layers in Silicon with Massive Molecular Ion Beam of Ir4(CO)7+

Tetrairidium dodecacarbonyl, Ir4(CO)12, is a massive compound called metal cluster complex, which has a molecular weight of 1104.9. Using an Ir4(CO)7+ primary ion beam, secondary ion mass spectrometry (SIMS) of boron-delta-doped silicon samples was performed. Depth resolution, defined by 1/e decay length for the trailing edge of the boron delta layer, was investigated in the beam energy ranging from 2.5 to 10 keV at an incident angle of 45°. Experimental results showed that the depth resolution improved with oxygen partial pressure at a beam energy of 5 keV. It was confirmed that the depth resolution without oxygen flooding monotonically improved as beam energy decreased. Furthermore, it was found that the favorable effect of oxygen flooding on depth resolution weakened as beam energy was reduced.

Ion Beam Generation from an Electrolyte Solution Containing Polyatomic Cations and Anions for Secondary Ion Mass Spectrometry

A solution-type ion beam source was fabricated to utilize polyatomic anions as well as polyatomic cations that are stable in solutions. The ion source consists of an electrospray section at atmospheric pressure and a vacuum section with a differential pumping system. To demonstrate the beam generation of cations or anions, ethanol solution containing a room-temperature molten salt (i.e., an ionic liquid) was tested. The ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, consists of a polyatomic cation, [C8H20ON]+, and a polyatomic anion, [C2F6NO4S2]-. Ions produced at atmospheric pressure were passed through an aperture into a vacuum chamber and then transported to a target. The effects of the aperture dimensions were investigated in the range from 50 to 200 µm in diameter and 0.25 to 1 mm in thickness. The ratio of current passing through the aperture into the vacuum chamber to the total electrosprayed current was on the order of 10-3 to 10-5. The ratio increased with increasing aperture diameter. A reduction in the aperture thickness also improved the ratio. Beam current increased with applied voltage in both positive-ion and negative-ion modes. It was demonstrated that stable negative-ion beams as well as positive-ion beams on the order of pA were produced.

Beam-induced Nanoscale Ripple Formation on Silicon with the Metal-Cluster-Complex Ion of Ir4(CO)7+

The surface topography of Si(100) bombarded with 2.5–10 keV Ir4(CO)7+ at an incident angle of 45° was investigated by atomic force microscopy. Experimental results showed that self-organized ripple structures with a wavelength below 30 nm were produced at a beam energy of 5 keV. It was found that the wavelength of the ripples increased with decreasing beam energy, which is different from results obtained using conventional ion beams. In addition, surface roughness proved to increase with decreasing beam energy. The phenomena were explained by considering a substantial decrease in sputtering yield and the subsequent compositional change in the target at lower-beam-energy Ir4(CO)7+ bombardment. Furthermore, the surface roughness was also confirmed to increase with increasing oxygen partial pressure.

Emission Characteristics of O- Ions from a Bare Surface of Yttria-Stabilized Zirconia (YSZ) at Elevated Temperatures

Thermionic emission of oxygen negative ions, O-, from a bare surface of yttria-stabilized zirconia (YSZ) was studied with a quadrupole mass spectrometer equipped with an energy filter, which is capable of detecting negative ions. Emission characteristics of O- ions were investigated at temperatures ranging from 725 to 925°C under pressures of 1.4×10-4 to 3.2×10-4 Pa. Mass spectra of emitted negatively charged particles showed that O- ions are emitted into a vacuum from the bare YSZ surface at elevated temperatures. By examining the energy distributions of O- ions, the number of emitted O- ions was found to increase with the temperature of YSZ.

Increasing the intensity of protonated secondary ions in time-of-flight secondary ion mass spectrometry using a proton-conducting ionic liquid, diethylmethylammonium trifluoromethanesulfonate

To increase the secondary ion intensities of organic molecules, room-temperature ionic liquids were investigated in two time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiments. First, ionic liquids as well as glycerol were tested as liquid matrices of arginine. The secondary ion intensity of protonated arginine was increased 200-fold by using a proton-conducting ionic liquid, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]). The matrix effect of [dema][TfO] was higher than that of glycerol, which is a typical matrix in SIMS. Next, ionic liquids were tested as primary ion beams. The number of protonated secondary ions of arginine was significantly increased by using a primary ion beam of [dema][TfO].