Search

The lead authors failed to name two collaborators as co-authors. The authors listed should include: Miss Claudia L. Compean-Gonzalez (ORCID: 0000-0002-2367-8450) and Dr. Giacomo Ceccone (ORCID: 0000-0003-4637-0771). These co-authors participated in VAMAS project A27, provided data that were analyzed and presented in this publication (and supporting information), and reviewed the manuscript before submission.

An orthogonal acceleration Time-of-Flight Secondary Ion Mass Spectrometer (TOF-SIMS) system has been developed with a metal-cluster-complex ion source. The ion source can produce ion beams of massive molecules called metal-cluster-complexes such as Ir 4 (CO) 12 , which has a molecular weight higher than 1000 u. Using the system, TOF-SIMS of a contaminated silicon substrate and a room temperature molten salt (i.e. an ionic liquid) was performed. The ionic liquid N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, which has a molecular weight of 426 u, consists of a polyatomic cation, [C 8 H 20 ON] + , and a polyatomic anion, [C 2 F 6 NO 4 S 2 ] - . During SIMS analysis, an analytical sample was bombarded with a continuous primary ion beam of either Ir 4 (CO) 7 + or Ar + in a beam energy of 10 keV at an incident angle of 45°. It was confirmed that the use of Ir 4 (CO) 7 + ions enhanced secondary ion intensity compared with that of Ar + ions. Also, experimental results showed that the bombardment of Ir 4 (CO) 7 + caused less fragmentation. In the case of the ionic liquid, cation-attached ionic-liquid molecules were observed in addition to the cation of the ionic liquid.

To develop a solution-type ion beam source utilizing a wide variety of metal cluster complexes that are stable only in organic solvents, we have investigated an electrospray method for transferring ions from solutions to gas phase. As initial experiments, we have studied electrospray characteristics of ethanol solutions containing a room-temperature molten salt (i.e., an ionic liquid) and acetic acid as alternatives to solutions of metal cluster complexes. In electrospray experiments, we used a stainless-steel capillary with an inner diameter of 30 μm. Experimental results showed that electrosprayed currents increased with applied voltage in both positive-ion and negative-ion modes. In addition to positive currents, stable negative currents were also confirmed to be produced. Current exceeding 250 nA was produced at 2 kV with a flow rate of 2 μL/min at a concentration of 1 × 10−3 mol/L. It was confirmed that several nA out of electrosprayed currents were delivered through an orifice (120 μm internal diameter) into a vacuum chamber. Experimental results indicate that the electrospray method seems to be applicable to an ion beam source for utilizing massive metal cluster complexes in solutions.

Superconducting tunnel junction (STJ) detectors are promising for energy-dispersive X-ray spectroscopy. We are developing array detectors with a sensitive area of 4 mm2, which consist of 100 of Nb/Al/AlOx/Al/Nb STJs having a size of 200 × 200 μm2 in order to obtain a good statistic for a short measurement time while keeping an excellent energy resolution for element selection in X-ray material analysis. In the course of this development, we analyzed the microstructures of the layers of Nb, Nb/Al, Nb/Al/AlOx/Al and Nb/Al/AlOx/Al/Nb deposited on Si substrates by using AFM (Atomic Force Microscope) and cross-sectional TEM (Transmission Electron Microscope). We found that the grain sizes of the polycrystalline films and the interface boundaries in the top electrodes are quite different from those in the bottom electrodes in a nanometer scale. It is expected that these different microstructures cause different heights of the pulse signals for the X-ray photon absorption events in the top and bottom electrodes.

Superconducting-tunnel-junction (STJ) array detectors with an effective sensitive area of 4 mm2 were fabricated for mass spectrometry. An array detector has one hundred Nb/Al/AlOx/Al/Nb junctions with a 200 mum-square sensitive area. The junctions are quasi-horizontally arranged on a 10 mm-square chip. In the course of fabrication processes, we have found that an anomalous nanometer-step structure appears within the junctions located in the outer region of the array detectors at a specific stage of the fabrication processes. The anomalous steps cause an increase of the leakage current from ~5 nA to a few 100 nA. In order to characterize and prevent the step structure formation, we performed structural analyses with atomic force microscopy, interference microscopy, differential interference contrast microscopy, and transmission electron microscopy. Vertical fault and blister formations were identified in the junctions around the periphery of the array arrangement even on a low stress sputtering condition of 40 MPa. In addition, it is reasonable that a horizontal slip in the AlOx barrier layer is induced by a nanoscale plastic deformation, which causes the large increase of the leakage current.

Metal cluster complexes are chemically synthesized organometallic compounds, which have a wide range of chemical compositions with high molecular weight. Using a metal cluster complex ion source, sputtering characteristics of silicon bombarded with normally incident Ir4(CO)7+ ions were investigated. Experimental results showed that the sputtering yield at 10 keV was 36, which is higher than that with Ar+ ions by a factor of 24. In addition, secondary ion mass spectrometry (SIMS) of boron-delta-doped silicon samples and organic films of poly(methyl methacrylate) (PMMA) was performed. Compared with conventional O2+ ion beams, Ir4(CO)7+ ion beams improved depth resolution by a factor of 2.5 at the same irradiation conditions; the highest depth resolution of 0.9 nm was obtained at 5 keV, 45° with oxygen flooding of 1.3 × 10−4 Pa. Furthermore, it was confirmed that Ir4(CO)7+ ion beams significantly enhanced secondary ion intensity in high-mass region.

In order to develop fabrication processes for superconducting tunnel junction (STJ) array detectors for time-of-flight mass spectroscopy, we have focused on a roughness of film surface and a residual stress of each deposited film in a layer structure of Nb/Al/Al 2 O 3 /Al/Nb. The roughness of each film depending on pre-treatments of silicon substrates and deposition conditions of Al and Nb films was studied by using an atomic force microscope (AFM). The dependence of the residual stress of the Al and Nb films on Ar gas pressure was evaluated by using an interference microscope. It was found that the Al thin film has a very smooth surface with a roughness of 0.79 nm in case of deposition on silicon substrates cleaned by a wet and dry process and in contrast, the surface roughness of the Nb and Nb/Al film are the smallest of 0.4 nm and 1.0 nm, respectively, on the Si substrate cleaned by only a dry process. We found appropriate sputtering conditions at which Al and Nb films have the stress less than 10 MPa, respectively. Those low stress conditions have to be realized in order to achieve a high reproducibility of STJ characteristics at each process run. The optimum deposition conditions for Nb and Al films were obtained for the STJ fabrication.

The STJ array detectors with an effective detection area of 4 mm2, which consist of 100 Nb/Al-AlOx/Al/Nb junctions with a size of 200×200 μm, have been fabricated. In order to improve the reproducibility of the STJ array fabrication, we investigated a correlation between the junction surface structures and the leakage currents. It has been found that the junctions near the fringe of the array detectors have a step of about 5 nm at the middle of the array detector, of which leakage currents are considerably larger than 1 μA. The step structure was formed after the etching of the bottom Nb layer for complete separation of Nb/Al/AlOx/Al/Nb/Si. In case of the sputtered Nb/Al/Nb/Si multilayers without 1 nm-thick tunneling barrier, no stepped surface was observed even after the bottom Nb layer etching. Therefore, it is apparent that the 5 nm step structure is a cause of the large leakage currents. We solved the step-fringe problem by a kind of extra patterning along the fringe of the array or lift-off patterning of the Nb/Al multilayers. It is concluded that the number of the junctions with the step structure depends on a slight difference in film deposition or etching conditions.

In order to reduce CO2 emissions, the European Union commenced an experimental approach called the “NaturalHy Project” in May 2004 to transport a mixture of hydrogen and the existing high-pressure natural gas in pipelines. NaturalHy denotes a mixture of hydrogen and natural gas. The properties of hydrogen-methane mixed gas should be investigated in detail because this gas is expected to replace methane as an energy carrier in the near future. Thus, the results of the authors would be useful to the researchers involved in developing pumps, compressors, or mass flow controllers for the next generation energy systems. To the best of their knowledge, this article is the first report on the viscosity measurement of hydrogen-methane mixed gas by using a quartz friction gauge. The authors measured viscosity using two methods for the purpose of comparison. In the first method, the pressure drop was measured in a laminar pipe flow. The authors prepared an electrically polished ultraclean smooth tube and carefully ...

Initial oxidation via ozone on the Si(1 0 0) surface is investigated by measuring surface stress and observing atomic structure via a scanning tunneling microscopy (STM). A similar investigation is also carried out for molecular oxygen and the results are compared. As a result, monotonic increase of the surface stress to the compressive stress side is obtained up to 0.33 N/m for ozone oxidation at room temperature, while molecular oxygen shows only tiny surface stress growth. From the STM observations, it is found that the difference between ozone and molecular oxygen oxidation is the existence of surface etching. As the origin of the surface stress, therefore, the reduction of the intrinsic tensile surface stress due to the reconstructed surface by the etching process is proposed.

In this work, we present a novel method for hydrogen sensing, based on partial pressure measurements with a diaphragm and a quartz friction pressure gauge (D- and Q-gauges, respectively). The D-gauge measures absolute pressure, whereas Q-gauge readings are affected by viscosity changes occurring when hydrogen is mixed with air, thus enabling H 2 detection. The new method is safe and sensitive and has a quick-response to hydrogen leakage. The measured minimum detection limit for hydrogen is 0.05 vol.% in air, and the response time to hydrogen introduction is less than 1 s; these characteristics are practically sufficient for hydrogen sensing.

A cluster-ion source has been developed to produce stable ion beams of metal-cluster-complex ions. As a metal cluster complex, triosmium dodecacarbonyl, Os 3 (CO) 12 , was used, which has a molecular weight of 906.7. Using the ion source, energy dependence of beam current and sputtering yield of silicon bombarded with Os 3 (CO) n + (n = 7-8) were investigated at beam energies from 2 to 10 keV under the normal incidence condition. By high-resolution Rutherford backscattering spectrometry (HR-RBS), a silicon target bombarded with the normally incident Os 3 (CO) 7-8 + ions at 10 keV with oxygen flooding at 5 × 10 -4 Pa was analyzed. The experimental results showed that the ion-beam current increased almost linearly with the acceleration voltage. It was found that the sputtering yields of silicon with Os 3 (CO) 7-8 + ions varied substantially with beam energy. The sputtering yield with Os 3 (CO) 7-8 + at 10 keV was higher than that with SF 5 + or Ar + by a factor of 3-20, whereas the yield at 3 keV was lower than that with Ar + . In the case of 2 keV, deposition was found to occur on the silicon surface. The substantial variation in the sputtering yield with beam energy would arise from the lower kinetic energy of each atom constituting the metal-cluster-complex ions. From HR-RBS results, it was confirmed that the constituent atoms of the Os 3 (CO) 7-8 + ions, Os, C, and 0, were implanted into the silicon target. The observed depth profiles of Os and C atoms were in good agreement with results of TRIM simulation, while that of the 0 atom was significantly different from the simulation results. The depth profile of the 0 atom was examined in terms of oxygen diffusion and implantation.

We investigated the ozone oxidation characteristics on a hydrogen-terminated Si substrate. A high-concentration ozone gas generator with an ozone condensation unit was specially designed and assembled for this study. During the oxidation by ozone with the concentration of 25 vol.% in the temperature range from 340°C to 625°C at 8 Torr (1.1 kPa), the formed oxide film thickness increased with oxidation time in accordance with the parabolic law, which suggests a diffusion-controlled step, while the oxidation by pure oxygen attained saturated states within 3 min of initiating oxidation. The activation energy for parabolic constants in the ozone oxidation was determined to be 0.52 eV. This value is much smaller than the activation energy for dry oxidation with oxygen, while it is almost the same as that in the plasma oxidation with the mixture of rare gas and oxygen. Moreover, the quality of the ozone oxidation film was evaluated by estimating the amount of suboxides (Si3++Si2++Si+) using x-ray photoelectron spectroscopy (XPS) analysis and the compressive stress using Fourier transform infrared (FT-IR) spectroscopic analysis. Both results showed that the quality of film subjected to ozone oxidation at 500°C is equal or superior to that of the film subjected to pyrogenic oxidation at 750°C in spite of the faster oxidation rate, and thus, the significant advantages of ozone oxidation at low oxidation temperatures could be confirmed.

We investigated a new method to measure the partial pressure of a binary gas system at near-atmospheric pressure conditions. The method utilizes two types of vacuum gauges, a capacitance manometer and a quartz friction pressure gauge. The partial pressure of the binary gas can be estimated by measuring the impedance change with a quartz friction pressure gauge, which depends on both viscosity and total pressure of a binary gas, and considering the total pressure change as measured by a capacitance manometer. We applied this method to measure the partial pressure of ozone in an ozone–oxygen gas mixture. The results suggested that the new method allows a partial-pressure measurement of ozone with an accuracy of Δ p =0.2 kPa , close to atmospheric pressure. The advantages of the new method include compact size, high safety standards when measuring highly reactive gases, and the allowance for in-line monitoring.

A concentration measuring method for a binary gas system, which was based on the viscosity measurement, was investigated. The method utilizes two types of pressure gauges, a capacitance manometer which depends just on pressure and a quartz friction pressure gauge which depends on both viscosity and pressure of a binary gas. The concentration of the binary gas can be estimated from the viscosity because the viscosity is given as a function of concentration of the binary gas. Firstly we applied the pressures-observing system to evaluate concentration of ozone in an O3/O2gas mixture. The results indicated that this method allows a concentration measurement of ozone with an accuracy ofΔ Cozone = 0.2 vol%, near atmospheric pressure. Secondly, we used an impedance measurement system of a quartz oscillator and we estimated the accuracy at Δ Cozone=0.05 vol%.

We have investigated the characteristics of silicon oxidation by concentrated ozone gas through the comparison of the oxidation by oxygen molecules. A sophisticated high-concentration ozone generator, which exploits the ozone/oxygen gas separation technique with silica gel, has been developed for the study. The generator can continuously supply ozone-oxygen mixtures with ozone concentrations up to 30 at.% at one atmospheric pressure. Ozone gas with a concentration of 25 at.% from the generator formed SiO2 films as thick as 2 nm and 6 nm on Si for a 30 min. exposure at 200°C and 600°C, respectively. On the other hand, oxygen gas by itself could form SiO2 films with only 1 nm and 3 nm thickness, respectively, at the same conditions. Moreover, in the oxide film formation at 600°C, the oxide film growth by ozone was proceeded with an oxidation time in excess of 240 min., while it saturated within very short time in the oxidation by oxygen. These phenomena verify the strong oxidation power of ozone. In addition, we confirmed that the growth rate of the silicon oxide with ozone dramatically changed when the substrate temperature was over 500°C, and this suggested the change of oxidation mechanism at this point. However, such a characteristic was not found in oxidation with oxygen.

Ozone is a strong oxidant due to its release of atomic oxygen. The initial ozone oxidation process at room temperature and the roughness of the interface were investigated using scanning tunneling microscopy (STM). The most favorable adsorption site was the bridge site on the Si dimer at initial oxidation using ozone gas. Less than 10% of the oxygen atoms on the surface were located at the bridge site between the Si dimers. The rest of the oxygen atoms were inserted into the backbond below the Si dimer atom near the defects. This indicates that the oxygen atom is inserted into the backbond of the Si dimer through original and etched defects. The interface of SiO 2 /Si was characterized after the oxide film was removed by hydrofluoric acid. STM images were obtained from the etched surface. The roughness of the STM image was below 0.2 nm rms. This result indicates that the interface between the silicon and ozone oxides limits the roughness to two to three SiO 2 layers at most after oxidation by ozone.

To measure concentration of binary mixture gas we developed a new method that uses a Quartz gauge together with a capacitance manometer. Because a Quartz gauge's sensor is sensitive to both gas viscosity and gas pressure while a capacitance manometer is just sensitive to gas pressure, the viscosity of the gas can be estimated from pressure indication from both the gauges. If the gas is binary mixture gas and the viscosity of the gas changes monotonically with the concentration, the pressure deviation will give the concentration of binary mixture gas. This method has several merits. One is that we can apply to explosive gases because the sensors do not have any source to ignite such as a heated wire, an energetic light, and an electron source. The other is that because of no source to decompose the gas, this method does not change the concentration of the sample gas after the measurement. Then it is not necessary to discard the sampled gas, and consequently the effective amount of the sample is negligible.

The effects of high-concentration ozone gas (~25%) exposure at atmospheric pressure with and without ultraviolet (UV) irradiation to a 4H–SiC(0001) surface has been investigated by X-ray photoelectron spectroscopy (XPS). The C 1s XPS spectrum for the 4H–SiC surface after standard RCA cleaning showed the appearance of a chemically shifted peak on the higher binding energy side of the SiC bulk peak. The chemically shifted peak was also observed even for the surface prepared by dipping a sample with sacrificed oxide film into 5% HF solution. Curve-fitting analysis using the Gaussian function revealed that the chemically shifted peak consisted of three components. The chemically shifted peak could be sufficiently eliminated using ozone exposure with UV irradiation. The cleaning mechanism of the 4H–SiC surface by ozone exposure is discussed, referring to the analysis of peak intensity for each component under different surface conditions corresponding to RCA cleaning and ozone exposure with and without UV irradiation.

We investigated the initial oxidation of Si(100) with ozone by comparison with oxidation by oxygen molecules using a specially fabricated ozone generator that could supply concentrated (typically 30 at.%) ozone gas at 1 atm pressure. We measured the thickness of the SiO 2 film on the Si by XPS, using a thermal oxide film with a known thickness as a reference. We observed the growth of an SiO 2 film on Si by ozone even at a sample temperature of 200°C, verifying the strong oxidation power of ozone. The SiO 2 film was ∼2.3 nm thick for 100 min of exposure. The kinetics of oxidation with ozone showed a power law dependence relative to exposure time, with almost the same power value for the ozone gas at 1 atm as at 2000 Pa. However, the growth of the SiO 2 film was saturated at the level of one monolayer when the ozone gas was supplied at 10 -4 Pa, which suggests to us a rapid decrease of the sticking (or reaction) probability of ozone on monolayer SiO 2 .

We have investigated ultrathin silicon oxide film growth by highly concentrated ozone at atmospheric pressure. Oxide film >2 nm was grown on as-received Si(100) even at room temperature. The etching rate by dilute hydrofluoric acid solution of oxide fabricated on Si(100) at 350 °C by this method was almost the same as that of thermally grown oxide so that film density is equivalent to that of thermally grown oxide. The etching rate of this film also shows no dependence on the film depth. This is indicating that the transition layer due to the lattice mismatch of substrate and oxide is limited within a thinner region than that of thermally grown oxide. It also indicates that an oxide film with higher film density can be synthesized on the surface with preoxide film already formed to protect bare substrate surfaces.

To understand the ultraviolet (UV)-ozone jet cleaning process of organic surface contamination layers, adventitious hydrocarbon layers on Si, self-assembled octadecyltrichlorosilane monolayers on Si, and self-assembled C60H–(CH2)12–SH monolayers on Au were cleaned with pure ozone jet and UV irradiation. Cleaned surfaces were analyzed with in situ x-ray photoelectron spectroscopy measurements. Ozone molecules could react with the unsaturated C–C bonds in self-assembled C60H–(CH2)12–SH monolayers on Au surfaces at room temperature. However, the saturated C–C bonds in OTS hydrocarbon molecules adsorbed on Au surfaces reacted not with ozone molecules but with oxygen radicals generated by the dissociation of ozone molecules under UV irradiation. For adventitious carbon contamination on Si surfaces, only a fraction could be cleaned by ozone at room temperature but it could be almost cleaned with UV-ozone jet.

A Ir4(CO)7+ primary ion beam, at energies from 2.5 keV to 10 keV, was used to profile boron-delta layers in Si to investigate the influences of atomic mixing and surface roughness on the degradation of depth resolution. Factorial analyses using the mixing-roughness-information (MRI) model indicated that the influence of the mixing increased as beam energy was reduced below 5 keV in the case of oxygen flooding. It was confirmed that the magnitude of the MRI surface roughness was different from that of the AFM surface roughness. The discrepancy in the magnitude of roughness was examined by considering the difference in sputtering depth as well as the definition of the MRI surface roughness.

To develop nanometric film thickness standard (FTSs), uniformity of silicon dioxide thin film were investigated by X-ray Reflectometry (XRR). The samples we investigated were thermally grown oxides (O2-Oxides) and ozone-formed oxide(Ozone-Oxide). The O2-oxide were grown on Si(100) substrate at 1000°C and at 700°C. The Ozone-Oxide was grown at 750°C with the highly concentrated ozone gas. With XRR method the bulk-layer density of oxide films were analyzed for; the O2-Oxide formed at 700°C (D700), the O2-Oxide formed at 1000°C(D1000), and the Ozone-Oxide formed at 750°C (Dozone750). We also analyzed the transition-layer density of the O2-Oxide formed at 700°C (DTL700). The results showed the relation was D1000

Our partial pressure measurement for a binary gas with a quartz sensor can be applied to plasmas. In this study, the Q-sensor outputs, which depend on pressure, molecular weight and viscosity of gases, were compared to the results by gas analysis with a quadrupole mass spectrometer (QMS). For H2 plasmas, the Q-sensor outputs changed when discharges were turned on and off. On the other hand, the results from mass spectroscopy by the QMS showed the degas of carbon monoxide (CO) during the discharges. Since the changes of the Q-sensor outputs correspond to the CO production above, it can be concluded that the Q-sensor measurements can detect the gas composition changes in the plasmas, thereby, can be used as a simple gas analysis method compared to a conventional mass spectrometer.

We observed by surface second harmonic generation (SHG) that initial the rate of second harmonics (SH) intensity decay during ozone adsorption on nitrogen-preadsorbed Si(111) was four times faster than on clean Si(111)-(7×7) because of the adsorption not only of atomic oxygen but also of oxygen molecules released by the dissociation of incident ozone molecules. The temperature dependence of the adsorption rate on nitrogen-adsorbed Si(111) was opposite to that on the clean Si(111)-(7×7) surface, but similar to that of molecular oxygen on Si(111)-(7×7). With increasing surface temperature, the sticking probability lessened in a similar way to that of molecular oxygen. This suggests that the sticking probability of molecular oxygen released by dissociating ozone molecules increases on nitrogen-adsorbed Si(111).

Initial oxidation by high purity ozone and molecular oxygen of Si(111)7×7 was investigated by second harmonic generation (SHG) with a 1.064 μm Nd:YAG laser. Decrease of second harmonics (SH) intensity to almost zero after 5 L ozone gas exposure, in spite of the fact that molecular oxygen kept SH intensity for the same amount of exposure, indicated that ozone is inserted into the Si–Si backbond in the subsurface layers more effectively than molecular oxygen. In the initial exposure, rates of rapid decrease in SH intensity for both ozone and oxygen adsorption were in the same order of magnitude, although O 1s x-ray photoelectron spectroscopy (XPS) intensity showed high reactivity of ozone. This is because of a difference in the information depth between SHG and XPS so that oxygen species in the subsurface layers are not effective in decreasing SH intensity. This indicates that the process of attacking backbonds is underway even with an initial exposure of

We observed an in situ process of ozone adsorption on Si(111)7 x 7 at different temperatures by second harmonic generation (SHG). On ozone exposure, the second harmonics (SH) intensity descreased close to a detectable limit on the surface at room temperature (RT). However, we observed the appearance of another SH intensity during ozone exposure at elevated substrate temperatures between 260°C and 400°C, after it decreased in the same way as that at RT. On these surfaces, the profile of SH intensity recovery by desorption of adsorbed species indicated that different adsorbed species were formed during surface exposure to ozone at different substrate temperatures: those at RT are weakly adsorbed species for termination of dangling bonds and insertion into backbonds, and those at higher temperatures have an Si-O-Si network which is more stable and desorbs at higher temperatures than 700°C. We conclude that the SH intensity that appeared on the surfaces at elevated temperatures is due to more stable SiO 2 -like Si-O-Si bonding as an initial step of oxide formation.

We have started the development of a new time-of-flight mass spectrometer equipped with Nb/Al superconducting-tunnel-junction detectors. Metal cluster ions were employed to investigate the properties of the superconducting ion detectors. In addition to mass spectroscopy with wide mass range, we have performed impact energy measurement, which enables charge-state discrimination.

Taking into account the utilization of partial pressure measurement under various temperatures and humidity, their influence on this measurement with a capacitance manometer and a quartz friction pressure gauge (Q-gauge) is studied. With increasing humidity, a Q-gauge pressure reading, calibrated by air gas, decreases as well as when the hydrogen leakage is detected. To avoid this error by humidity for the hydrogen sensing, we tried to compensate influence of humidity using a humidity coefficient which is calculated from the humidity dependence of the Q-gauge pressure reading at constant temperature, and suppressed to one-fifth of the fluctuation of the Q-gauge pressure reading background due to humidity change. Regarding to influence of temperature on the Q-gauge pressure reading, it is calibrated by the temperature dependence at low humidity. Finally, influences of temperature and humidity on the hydrogen sensing can be reduced by the calculation below the reading by 0.6 at.% of hydrogen gas.

For safety hydrogen sensing, the pressure measurement with a capacitance manometer and a quartz friction pressure gauge (Q-gauge) were investigated. Q-gauge pressure reading decreases when hydrogen gas is introduced into air supplied from atmosphere without any change of pressure measured by a capacitance manometer. This result indicates that the present pressure measurement using two pressure gauges is possible to detect the hydrogen leakage into air. In addition, a decrease of Q-gauge pressure reading correlates with a flow rate of the hydrogen gas, and increases with hydrogen concentration in air. Then it was shown that the low detection limit of hydrogen concentration is below 1%. Response time for hydrogen introduction is faster than 30 seconds, which meets the requirements for the hydrogen gas leak sensor. As above, the present safe pressure measurement using a capacitance manometer and a Q-gauge is satisfactorily useful for the hydrogen gas leak sensing.

Metal cluster complexes, including the colloidal metal cluster, were applied to establish the low damage sputtering method. Electro-spray-like ionization using an ink-jet nozzle has the potential to produce a cluster ion beam. A colloidal Au cluster of size 5 nm made a large crater-like hole at the carbon sheet. Copyright © 2005 John Wiley & Sons, Ltd.

In order to increase the ion-detection efficiency of the pressure measurement method using nonresonant multiphoton ionization, an ion-detection head was improved. Using this head, pressure measurements were carried out for H2 and Xe in the extreme high vacuum region. As a result, for H2, by optimizing an incident ion energy, the efficiency increased by a factor of about 2.5. For Xe, without optimizing the incident ion energy, it increased by a factor of about 1.5.

The second harmonic of a picosecond Nd:YAG laser was used to nonresonantly ionize Xe atoms in vacuum. The spatial distribution of the produced ions was observed by our ion-imaging method. Time of flight spectrum of the produced ions was also measured simultaneously. Xe2+ and Xe3+ ions were detected around the center of the ionization volume. The produced amount of multiply charged ions decreased rapidly with the distance from the center of ionization volume comparing to that of Xe+ ions. The present method can be applied for the simultaneous measurement of total and partial pressure.

By means of nonresonant multiphoton ionization using a picosecond pulsed YAG laser, pressure measurement for H2, CO and CO2 gases was carried out in the XHV pressure range. It was experimentally verified that pressure measurement was possible in the range of 10-11 Pa, and this pressure measurement method had pressure sensitivity of the same order of magnitude for the three molecules.

Lanthanum oxide thin films were fabricated on Si substrates by the metallorganic chemical vapor deposition (MOCVD) method at substrate temperatures ranging from 400 to 650°C. From the results of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), cross-sectional scanning transmission electron microscopy (STEM), and energy-dispersive X-ray (EDX) analyses, the enhanced chemical reaction at the interface between the Si substrate and the films was revealed, which results in the generation of an interfacial layer of SiO 2 (1-2 nm thick) and lanthanum silicate at all the experimental substrate temperatures. We found that a thin silicon oxynitride layer on the Si substrate is effective in suppressing the interfacial reaction and in increasing the dielectric constant of the lanthanum oxide deposited on it. The thin silicon oxynitride layer is also effective in reducing the leakage current through the film. For the stacked La-oxide/SiON film, the dielectric constant of the lanthanum oxide film was 19 and the leakage current density was 3 X 10 -6 A/cm 2 at the oxide voltage of 1 V for a film with an equivalent oxide thickness of 2.4 nm.

In order to increase the ion-detection efficiency of pressure measurement using nonresonant laser ionization method, a Channeltron of aperture 19mm was used in the ion-detection head and pressure measurement was carried out with H2. The detection efficiency was increased about 1.5 times compared to a previous result. The volume of the ionization region estimated from the present measurement, 5.8 × 10−4 mm3, is close to that derived from the direct observation of the ion distribution in the ionization region, 6.4 × 10−4 mm3.