Atsuya Chiba

Improvement in electrical performance of radiation-damaged silicon solar cells by annealing

Abstract We have examined the temperature dependence of radiation damage for silicon solar cells that are exposed to γ-rays, and attempted the improvement of electrical performance of radiation-damaged solar cells via annealing. The power output of the solar cells was measured continuously during γ-irradiation and annealing. Although the power output decreases with increasing temperature during γ-irradiation, the resistance against radiation damage with respect to the power output was enhanced. When annealed after γ-irradiation, the solar cells generated a power output having a structural form that was determined by the depth or the number of donors or acceptors existing in the depletion layer of the solar cells, and the electrical performance of the solar cells was improved. In addition, solar cells were damaged by neutron irradiation; however, the electrical performance was not improved by annealing.

Secondary ion counting for surface-sensitive chemical analysis of organic compounds using time-of-flight secondary ion mass spectroscopy with cluster ion impact ionization

We report suitable secondary ion (SI) counting for surface-sensitive chemical analysis of organic compounds using time-of-flight (TOF) SI mass spectroscopy, based on considerably higher emission yields of SIs induced by cluster ion impact ionization. A SI counting system for a TOF SI mass spectrometer was developed using a fast digital storage oscilloscope, which allows us to perform various types of analysis as all the signal pulses constituting TOF SI mass spectra can be recorded digitally in the system. Effects of the SI counting strategy on SI mass spectra were investigated for C(8) and C(60) cluster ion impacts on an organically contaminated silicon wafer and on polytetrafluoroethylene targets by comparing TOF SI mass spectra obtained from the same recorded signals with different SI counting procedures. Our results show that the use of a counting system, which can cope with high SI yields, is necessary for quantitative analysis of SI mass spectra obtained under high SI yield per impact conditions, including the case of cluster ion impacts on organic compounds.

Laser detection of surface acoustic waves as a method of measuring an Ar ion beam modification of carbon thin film

Pulsed energy impacts are expected to generate the elastic waves reflecting the elastic properties of impacted substances. Among the generated waves, the surface acoustic waves (SAWs) can be more specific to the surface structures and can be used effectively in the characterization of thin films in a non-destructive way. In the present study, pulsed laser impacts were employed to generate SAWs on a thin film and the SAWs are detected with a laser reflection technique. To test the effectiveness of this method, an amorphous carbon films were irradiated with 13 keV Ar ions at room temperature in a broad range and the SAW propagation velocity was evaluated as a function of Ar ion dose. The present preliminary experiment using pulsed laser suggests the successful detection of SAW from typical substances with different modulus of elasticity such as fcc metals, oxides and semi conducting materials.

Transmission of cluster ions through a tandem accelerator of several stripper gases

The transmissions of carbon cluster ion beams through a tandem accelerator using several stripper gases (He, N2, CO2, and SF6) with a terminal voltage of 2.5 MV were measured as a function of the gas pressure in investigating the most suitable gas for cluster ion acceleration. This resulted in it being demonstrated that the highest transmission could be obtained using the smaller size gas, i.e., helium displayed the best performance of the four gases used. In addition, the ratio of transmissions of C(n) with helium and nitrogen increased with increases in the n, thus revealing that helium gas should prove the most effective in larger cluster ion acceleration using the same energy.

Organic Contaminant Detection of Silicon Wafers Using Negative Secondary Ions Induced by Cluster Ion Impacts

Emission yields of carbon and hydrogenated carbon cluster secondary ions CpHq± (p≥1, q≥0) originating from organic contaminants on a silicon wafer are compared between monoatomic (0.5-MeV/atom C1+) and cluster ion (0.5-MeV/atom C8+) impacts using time-of-flight (TOF) secondary ion mass spectrometry. CpHq- for the cluster ion impact exhibits the highest emission yield per incident atom among CpHq± with the same p number. The highest relative CpHq- emission yield for the cluster ion impact reaches ~20 and ~60 times higher in comparison with those of CpHq- and CpHq+ with the same p number for the impact of the monoatomic ion with the same velocity, respectively. Combination of negative secondary ion TOF measurements with cluster impact ionization is a promising tool for highly sensitive detection of organic-contaminants on silicon wafers.

Surface-sensitive Chemical Analysis of Organic Insulating Thin Films Using Negative Secondary Ions Induced by Medium Energy C60 Impacts

We report on the surface-sensitive chemical analysis of organic insulating thin films using negative secondary ions (N-SIs) induced by C60 impacts in the medium energy range from several tens to several hundreds keV. The incident C60 energy dependence of emission yields of characteristic N-SIs for poly(methyl methacrylate) and charging effects on the N-SI mass spectra were investigated using time-of-flight SI mass spectrometry. Our results show that medium energy C60 impacts stably provide considerably high characteristic N-SI yields without charge compensation, and demonstrate that time-of-flight SI mass spectrometry with medium energy C60 impacts is advantageous for the highly-sensitive chemical analysis of organic insulators.

Status of ion sources at the national institutes for quantum and radiological science and technology (QST)

The National Institutes for Quantum and Radiological Science and Technology (QST) manages various types of ion sources for research and development in the fields of life sciences, medical and industrial applications, and fusion energy science. The QST is currently developing on electron cyclotron resonance ion sources, negative ion sources (ion sources for fusion and for tandem accelerators), ion sources for radioactive beams, laser ion sources, and miscellaneous ion sources. Its intra- and inter-institutional collaborations make QST a promising platform for future ion source technologies.The National Institutes for Quantum and Radiological Science and Technology (QST) manages various types of ion sources for research and development in the fields of life sciences, medical and industrial applications, and fusion energy science. The QST is currently developing on electron cyclotron resonance ion sources, negative ion sources (ion sources for fusion and for tandem accelerators), ion sources for radioactive beams, laser ion sources, and miscellaneous ion sources. Its intra- and inter-institutional collaborations make QST a promising platform for future ion source technologies.

Time-of-flight secondary ion mass spectrometry with transmission of energetic primary cluster ions through foil targets

We developed time-of-flight (TOF) secondary ion (SI) mass spectrometry that provides informative SI ion mass spectra without needing a sophisticated ion beam pulsing system. In the newly developed spectrometry, energetic large cluster ions with energies of the order of sub MeV or greater are used as primary ions. Because their impacts on the target surface produce high yields of SIs, the resulting SI mass spectra are informative. In addition, the start signals necessary for timing information on primary ion incidence are provided by the detection signals of particles emitted from the rear surface of foil targets upon transmission of the primary ions. This configuration allows us to obtain positive and negative TOF SI mass spectra without pulsing system, which requires precise control of the primary ions to give the spectra with good mass resolution. We also successfully applied the TOF SI mass spectrometry with energetic cluster ion impacts to the chemical structure characterization of organic thin film targets.